Work-a-text in physical science (Cambridge work-a-text)

Work-a- Text in

PHYSICAL SCIENCE MILTON GALEMBO

Science Department Cleveland Hill High School Cheektowaga, New York OTHO E. PERKINS

Supervisor of Science Columbus Public Schools, Columbus, Ohio Edited by JAC K ROBBINS

District Supervisor of Science Long Beach City School District, Long Beach, New York BURTON E. NEWMAN

Chairman Science Department Lakeland High School Shrub Oak, New York

CAMBRIDGE BOOK

�

NEW YORK, N.Y. A NEW YORK TIMES COMPANY

COMPANY

©Copyright 1971, 1966, by CAMBRIDGE BOOK COMPANY

A ll rights reserved. No part of this book may be reproduced in any form without the written permission of the publisher.

MANUFACTURED IN THE UNITED STATES OF AMERICA

PREFACE About a hundred years ago, the Brit ish Bureau of Pat ent s announced plans to close its doors because, according to it s director, all wort hwhile discoveries had already been made. Man had nothing more to learn! This was be­ f ore t he first successf ul airplane flight , bef ore t elevision, and bef oret he age of nuclear energy. Today, man realizes f ull well t hat although great discoveries about our environment have been made, much new knowled ge lies just beyond the horizon. In f act, new inf ormation is being accumulated in t he sciences at such a f antastic rate that our amount of knowledge doubles every five to ten years. As more knowledge is gained, science textbooks get big­ ger, bulkier, and more complicated. Teachers are daily f aced wit h t his challenging quest ion : "How can science be taught in an age when new knowledge becomes outdated almost over­ night? " Work-a-Text in Physical Science takes ad­ vantage of new discoveries in teaching and learning to help t eachers and students in this time of rapid change. Alt hough knowledge may change, and new ideas may become out­ moded, basic science principles, concepts, and processes are more stable. While including the most up-to-date inf ormation available, Work-a-Text in Physical Science is designed around an integrated program of these f unda­ ment al aspects of physical science. The ay tivities include various pr ocesses and science concepts, and promot e a logical approach t o problem solvi ng. This Work-a-Text is divided into two major sections, physics ( 1 4 chapters ) and chemistry ( 1 0 chapt ers ) . The teacher can elect to teach either the chemistry or the physics portions first, according to student needs, without dis­ rupting the overall program plan. The new Work-a-Text in Physical Science combines the best f eatures of a comprehensive text, laboratory manual, and activities book. It can be correlat ed with topics covered in all standard text books, and may be used with them or as t he basic classroom text. The reading m aterial of each chapt er is as up-to-date and authentic as research in physi-

cal science it self . The many illustrat ions and diagrams help t o clarif y im port ant concepts. The abundant review tests help to reinf orce processes as well as main ideas, and they em­ ploy a variety of approaches. The Self-Discovery A ctivities help t he st u­ dent s develop a f acilit y wit h t he processes of science by act ive part icipation in t he " doing of science." At t he same t ime main ideas and concepts are supported. The act ivities vary f rom induct ive to deductive in f ormat, and are a depart ure f rom t he old idea of " cook­ book experiment s" in science. Rather than be­ ing placed at the end of t he units, as in pre­ vious editions, t he Self-Discovery A ctivities are integrated wit h t he chapt er m aterial. Int his way, student s are involved in invest igat ions of a concept in a more relevant manner. Act ivities involve simple equipment which is r eadily available or easily improvised, and are de­ signed with t he saf et y of students in mind. Many of t he suggested activities m ay be car­ ried out by the student individually. Ot hers are bett er suited f or work wit h a laborat ory partner, or by larger student groups. The Review Tests are perf orat ed so they can be removed and handed in f or evaluation, if desired. These t est s can also be used t o review t he main ideas of t he chapt ers and can be " graded" by the student s t hemselves. See the teacher's guide m at erial f or f urt her ideas f or using the tests, which can save many hours of the teacher's planning t ime. When all t he unit s of t he Work-a-Text in Physical Science are completed, the student may be encouraged to keep t he book f or his own librar y. On completion of the course, he will have a written record of his work, and a comprehensive, i llust rat ed book t hat he will ref er to many times. Effective use of t he Work-a-Text in Physical Science will give teachers and student s more opportunity f or the exchange of ideas, and a clearer view of science and it s import ance t o man. It is hoped that it will also stimulat e the st udent to f urt her study on his own. -

THE AUTHORS

A C K N OWLEDG M ENTS The Author wishes to thank his many asso­ ciates who offered helpful advice and criti­ cisms and tested the exercises in their classes. My thanks go to Dr. Luis W. Alvarez and J anet L. Alvarez of the U niversity of Califor­ nia, and to This Week Magazine for permis­ sion to reprint the article entitled "Fallout Pro­ tection f or U nder 20 Cents." This article ap­ pears as a Self- Discovery Activity on pages

iv

130-132. Also f or permission to adapt dia­ grams from "Steel in the Making," published b y the Bethle hem Steel C orp oration. My hear tfelt appreciation goes to my wife Louise, who so meticulously typed the manu­ script and to the editori al staff of the C am­ bridge Book C o. , f or their wise counsel and their infinite p atience.

CONTENTS Preface

iii

Safety in the Laboratory

vii

The Scientific Method

viii

Archimedes'

Principle. Why Does an

Object Float? Why Does an Object Sink? Specifi c Gravity.

Determining Specific

Than Water. Specific Gravity of Liquids.

1

Spe cific Gravity. Bernoulli's Self-Discovery A ctivities. Review Tests. Uses

of

Principle.

7. Force s an d Mo tion . . . . . .. . . . . . .. . . . . . . .. . .. . .. . ...

Motion. Speed and Velocity. Uniform

Review Tests. 2. Ph ysic s an d the Me tric Sy ste m . . . . . . . . .. . . ..

Physics - the Science. The Metric Sys-

11

Bodies. Distance Covered by Moving Bodies. Newton's Three Laws of Motion. Conservation of Momentum.

ric

covery Activity. Review Tests.

of

Length,

Weight. Conversion

Volume,

and

Factors . Common

Review Tests.

Static Electricity. Dangers of Static Elec­

3. Forces . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . Gravitational Force. Mass. The Law of Gravitational Attraction . The Force of Friction. The Force of Inertia. Molecular Forces . Cohesion. Surface Tension. Ad­ hesion. Capillary Action. Force Vectors. Concurrent Forces . Self-Discovery A c­ 4. Force san d Work . . . . . . ... . .. . . ... . . . .. . . . . . . . . . ... . . and

Work.

Power?

Horsepower.

Law of Machines.

Measure Electricity.

Is

Work? What Machines.

9. Magne ti sm. . . . . . . . . . . . . . . . . ............................. Magnets. Theory of Magnetism. Electro­ magnets. Generators. Type s of Electrical Currents. Electric Motors. Self-Discov29

Is

How

Simple and Com­

81

ery A ctivities. Review Tests.

10. Sound

. . ................... ...............................

Is

Sound

Transmitted?

Sound

91

Waves. Velocity of Sound. The Pitch of

pound Machines. Levers. The

Law of Moments. Mechanical Advantage. In­ clined Plane. Other Simple Machines.

Sound. The Loudness of Sound. The Re­ flection of Sound (Echoes). Musical Sounds. How We Hear Sounds. Self-Dis­

Self-Discovery A ctivities. Review Tests.

Self-Discovery A ctivities. Review Tests.

Self-Dis­

covery A ctivities. Review Tests.

The

5. Pressure in Fluids . . . .. . . . . ... . . . . .. . . . . . . . . . . . . . . . . Density. Pressure. Liquid Pressure. Total Force. Total Force on a Vertical Sur­ face. Effect of Shape, Size and Volume on Pressure. Liquids Exert Pressure Equally in All Directions at the Same Depth. Pascal's Law and Hydraulics.

Ohm's Law. Electri-

cal Circuits. Power and Energy.

Potential Energy.

Kinetic Energy. What

69

tricity. Current Electricity. Units Used to

19

tivities. Review Tests.

Energy

Self-Dis­

8. Elec tr ci i ty . .............................................

Metric Units. Self-Discovery A ctivity.

61

and Accelerated Motion. Freely Falling

tem. Important Prefixes. Common MetUnits

51

Gravity of Solids Denser and Less Dense

AREA 1. INTRODUCTION TO PHYSICS

1. The Techniques and Tools of Science . . . . Using a Scientific Method III Solving Problems. Theories, Facts, and Laws. Superstitions . Scientific Equipment and Measurement. Self-Discovery A ctivity.

6. Buo yancy an d S peci fic Gra vi ty ..............

covery A ctivities. Review Tests.

41

11. Ligh t .. . .. . . . . . . . . .. .. . . .. . . . . .. . . . . . . . . ... . . . . . . . . . .. ... . .

The Nature of Light. Velocity of Light. Theories of Light. Properties of Electro­ m agnetic Radiations. The Electromag­

netic Spectrum. What Is Refraction? Dis­

persion of White Light. Color of an Ob­ ject. Reflection. Refraction. Convex

97

Lenses. Concave Lenses. Strength of a Source of Light. Photometry. Intensity of Illumination. Optical Instruments. Polar­ ized Light. Self-Discovery A ctivities. Re­ view Tests.

12. Hea t ........ . . . ........ . .................................. 109 Sources of Heat Energy. Heat and Tem­ perature. Measuring Temperature. Heat Transfer. Conduction. Convection. Ra­ diation. Effects of Heat Energy. Self-Dis­ covery A ctivities. Review Tests.

13. Nuclear Energy . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 The Development of Nuclear Energy. Nuclear Reactors. Nuclear Fusion. Uses of Nuclear Energy. Self-Discovery Ac­ tivity. Review Tests.

Self-Discovery A ctivity. Review Tests. .

19. The Periodic Table .......... . . . . . . . . . . . . . . . . . . . . . 171 Reading the Periodic Table. The Ar­ rangement of Elements Into Periods. Ar­ rangement of Elements Into Groups. Iso­ topes and Radioisotopes. Beneficial Uses of Radioisotopes. Self-Discovery A ctivity. Review Tests.

20. Wa ter . ... . . .... ......... ...................... ........... 181 Properties of Water. Types of Solutions. Suspensions. Colloids. Water Purification. Hard and Soft Water. Water Pollution. Self-Discol'ery Activities. Review Tests.

14. Civil Defense . .............................. . .......... 127 Surface, Subsurface, Underwater Bursts. Zones of Destruction. Radiation. Factors Influencing Radioactive Fallout. Protective Measures Against Radioactive Fallout. Basement Fallout Shelter. Self-Dis­ covery Activity. Review Tests.

AREA 2. INTRODUCTION TO CHEMISTRY

15. The Chemis try of Mat ter ........................ 137 Branches of Chemistry. Kinds of Matter. Natural Elements. Synthetic Elements. Transuranium Elements. Compounds. Major Differences Between Compounds and Mixtures. Self-Discovery A ctivity. Review Tests. .

16. Ma tter and Energy ....... . . . . . . . . .... . .......... . 145 The Molecular Theory of Matter. States of Matter. Properties of Matter. Physical and Chemical Changes. The Law of Con­ servation of Matter and Energy. Exo­ thermic and Endothermic Reactions . Self­ Discovery Activities. Review Tests.

17. Chemis try and the A tom ....... . . . .... . ......... 153 Structure of the Atom. Major Atomic Particles. Sub-Nuclear Particles. Atomic Weight. Formula or Molecular Weight. Electron Structure. Self-Discovery Ac­ tivity. Review Tests.

18. Chemical Ac tivi ty ...... . . ........... . ... . . . . . ...... 161 Metals and Non-metals. Activity Series of Metals. The Halogen Activity Series. vi

Formation of Compounds and Ions. Equations. Types of Chemical Reactions.

21. Acids , The Properties of Acids. Common In­ dustrial and Laboratory Acids. The Properties of Bases. Salts. Neutralization. Reaction Between an Active Metal and an Acid. Chemical Reaction Between a Base and a Salt. Self-Discovery A ctivity. Review Tests. .

22. Iron and S teel ................... . ... . ....... . . ... . . . 199 The Occurrence of Iron. The Metallurgy of Iron and the Use of the Blast Furnace. Steel. The Open-Hearth Furnace. The Basic Oxygen Furnace. Steel Alloys . Self-Discovery A ctivity. Review Tests.

23. Organic Chemis try ... . . . . . ... . . .............. . .. . . 207 Crystalline Forms of Carbon. Amor­ phous Carbon. The Compounds of Carbon. Hydrocarbons. Comparison of Or­ ganic and Inorganic Compounds. Some Members of the Methane Series. Self­ Discovery Activities. Review Tests.

24. Chemical Advances ......................... ....... 217 Health. Industry. Petroleum. Plastics. Rubber. Synthetic Fibers. Silicones. Con­ servation of Resources. Self-Discovery A ctivity. Review Tests.

Appen dices ............................................ 225 Distinguished Scientists. Important Scientific Laws and Principles. Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . 228 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 240

S O M E I M PO RTANT SAFETY RULES I N T H E LABORATORY Safety in the laboratory is essential to prevent serious accidents to yourself and to others. Heed the following directions and all directions given by your instructor. Most accidents can be prevented if you

MAKE SAFETY A HABIT!

1. Read and follow all directions very carefully.

2. Never mix, touch, taste, heat or inhale chemicals unless you are told it is all right to do so by your instructor.

3. Always wear protective devices such as goggles, gloves, and an apron when these safety devices are needed.

4. Handle all hot objects with clamps or tongs.

S. Take extra precautions in handling dangerous chemicals.

6. Do not perform any experiments unless your instructor is in the room.

7. Turn off the gas when it is not in use.

S. Read the labels on all bottles carefully before using.

9. Never point a test tube you are heating toward anyone.

10. Pay strict attention to your own work. Don't let your interest or at­ tention wander.

FIRST AID FOR ACID AND ALKALI BURNS 1. Flood the tissue with water.

2. Notify your instructor.

3. FOR ACID BURN: Neutralize with a weak alkali (base) such as a sodium bicarbonate solution.

4. FOR ALKALI BURN: Neutralize with a weak acid such as a boric acid solution.

S. When

mixing

acid

and

water - always

add

the

acid

to

the

water, using the greatest caution.

6. When inserting a glass tube into a cork, always lubricate the tube and cork with water.

7. The science laboratory is a place for inteUigent adult behavior.

vii

Gathers evidence

Reads others' works; listens to others

Gathering of evidence, etc., etc.

BUT-a scientist's work never ends-so

to

leads

to

APPLYING THE SCIENTIFIC METHOD

Chapter 1

T H E T EC H N IQU ES A N D TOOLS O F S C I E N C E What i s a "scientist? " I s a scientist a "spe­ cial" kind of per son? Not r eally; however , a scientist does have some special char acter istics. 1. A Scientist Is Curious. His cur iosity leads him to seek knowledge about his envir onment, and plants the seeds of new ideas that taker oot and gr ow.

2. A Scientist Investigates. Cur iosity is of little value if it doesn't lead to investigation. The scientist carr ies out his investigations in an or ganized manner . This appr oach to solving pr oblems is often called the scientific method. 3. A Scientist Is Logical. The scientist uses valid, ver ifiable evidence to suppor t his con­ clusions. He is not swayed by super stition. 4. A Scientist Is Open-minded. He r ealizes that the envir onment is always changing, and that his knowledge is often based upon incom­ plete evidence. He accepts new infor mation and uses it to change and impr ove his ideas. USING A SCI ENTI FIC M ETHOD IN SOLVING PROBLEMS

1. Identify the Problem to be Solved. In or der to identify and under stand a pr oblem, it must be limited to a single, clear ly defined

question. Then the scientist can pr oceed. The failur e of an investigation can fr equently be tr aced to a lack of under standing of what the basic pr oblemr eally is.

2. Gather Evidence. In or der to deter mine whether or not an idea has mer it, a scientist sear ches thr ough all available r efer ence mate­ r ials to see what has been done in the past to solve the pr oblem. When possible, he discusses his ideas with exper ts in the fi eld. This pr events him fr om needlessly r epeating tedious wor k that has alr eady been done by other s, and pr o­ vides clues that help him f or mulate tr ial solu­ tions to his pr oblem. 3. Make a Hypothesis. A tr ial solution to a pr oblem is a hypothesis. It is of ten called an " educated guess," bec ause it is based on what is lear ned as the scientist gather s evidence about the pr oblem. Sever al hypotheses may b e tested and r ejected bef or e the pr oblem is solved. 4. Test the Hypothesis. A scientist estab­ lishes a set of pr ocedur es to test his hypothesis. He keeps accur ate, up-to-date notes so that his r esults can be ver ified if he or other s later r e­ pe at the pr ocedur e under the same conditions. 1

To t est t he hypot hesis, an experiment oft en has t o b e carried out . In sett ing up a scient ific experiment, t he following guidelines are im­ port ant:

( a ) Using a Control. A cont rolled experi­ ment is set up in duplicat e. Procedures, ident ical in every way except one, are carried out . The st ep t hat is carried out in one procedure and omitt ed from t he ot her is known as t he variable. The variab le is t he part of t he invest igat ion t hat is designed t o t est t he hypot hesis. The proceduret hat includest he vari­ ab le is known as t he experiment. The procedure from which t he variab le was omit t ed is calledt he control. As an ex­ ample, suppose t hat a scient ist want ed t o check t he effect of heat energy upon t he product ion of elect rical energy in wires of different kinds ( see Self-Dis­ covery Act ivit y, Invest igat ing a Ther­ mocouple, page 113 ) . He obt ained 100 pieces of copper wire and 100 pieces of iron wire. Then he t wist ed about t wo inches of each piece of copper wire t o t wo inches of each piece of iron wire. He connect edt he loose ends oft he 100 pairs of wires t o a galvanomet er. He heat ed 50 oft he pairs wit h a burn er at t he point where t he wires were t wist ed t oget her, and he ob served and recorded any reading on t he galvanomet er. He connect ed t he remaining 50 pairs of wires t o t he galvanomet er and wit hout heat ing t hem ob served any reading. The scient ist t hen made his conclusions b ased upon his ob servat ions. ( b ) Using a Sufficient Number of Experi­ mental Sets. In t he preceding invest iga­ t ion, t he scient ist used t wo set s of 50 b ecause even carefully mat ched wires may have slight differences. By using many experiment al set s, any variab les t hat could cause invalid result s are less likelyt o affect t he invest igat ion. ( c ) Repetition. A scient ist doesn't rely on t he result s of one experiment t o draw 2

his conclusi ons. A n experiment should b e repeat ed and verified before it can b e considered valid. An experiment t hat cannot produce t he same result s when repeat ed under ident ical condi­ t ions cannot b e relied upon. S. Observe and Record. Accurat e and up­

t o-dat e records should b e kept of all ob serva­ t ions. Careful measurement s and t he accurat e present at ion of dat a prevent t he omission of import ant det ails. 6. Arrive at a Conclusion. Based upon t he evidence he has gat hered, his observat ions, and t he result s of any experiment s, t he scient ist t ries t o arrive at meaningful conclusions. He asks himself some searching quest ions. Was a sufficient amount of informat ion gained as he gat hered evidence t o draw a conclusion wit h­ out experiment at ion? Were his hypot heses properly relat ed t o t he b asic problem? Did t he variable in t he experiment ( or experiment s ) properly t est t he hypot hesis? Finally, were t he result s oft he experiment valid or reliable? Supposet he scient ist who didt he experiment wit h t he wires makes t he st at ement, "When dif­ ferent kinds of wires are t wist ed t oget her and heat ed, elect ricit y is produced." What are some fl aws in such a conclusion? Somet imes, t he conclusion will support t he ideas and hypot heses of t he scient ist , and t he prob lem is solved. Oft en, however, more ques­ t ions arise t o be solved, or experiment s show t he hypot hesis t o be incorrect, andt he scient ist must st art all over again. A negat ive conclu­ sion should not be considered a failure; it is just as valuable as is a posit ive result . Int est ing a hypot hesis, b ot h negat ive and posit ive result s give clues for furt her st udy. TH EORI ES, FACTS, AND LAWS

Scient ist s develop possib le explanat ions for various phenomena which are b ased upon some demonst rat ab le evidence. Such explanat ions are oft en called theories. Theories cannot usu­ ally b e proven "false" or "t rue." However, t hey provide a model from which t o proceed. For example, t here are several t heories relat ed t o

evolution all of which are based upon some observable evidence, but none of t hem has been proven "t rue" or "false." If a theory is proven t o t he satisfact ion of most scient ists, it is often called a science fact. However, even facts are subjectt o change when new information makes t he fact no longer vali d. A scientific law is est ablished whent he s ame results are cons istent ly observed without excep­ tion, although no satisfactory explanation may be available. We speak, for example, aboutt he Law of Gravitation, and aerospace scientists use it to determine precisely the orbits of space­ craft. Yet, we still do not know what gravity really is or what causes it.

t o make accurat e measurements. He must have basic m aterials and equipment wit h which to carry out investigat ions. Proper use of this equipment increases his accuracy in carrying out procedures, observing various phenomena, and making precise quantit at ive measurement s.

SUP ERSTITI ONS

( See also Chapter 2, Physics and the Metric System, pages 1 1 -18 . )

Do you carry a lucky coin or a rabbit 's foot ? Do you knock on wood or avoid walking under a ladder? These are superstitions. They can be traced to primitive peoples who did not under­ stand the laws of nature -t he lightning, rain, thunder, darkness and light. They believedt hat good and bad spirits caused things to happen, so they invented charms to make the evil spirits happy. They were afraid of what they didn' t understand and trusted in magic. Hundreds of years ago, people believed that living things could arise out of non-living things. They believedt hat mice were born from t he mud of t he N ile R iver, that worms and toads came from rain, and that if soiled rags were mixed with wheat grains, young rats would develop. These beliefs last ed u ntil about 1650, when an Italian physician, Francesco Redi, showed that flies and maggots do not come from rott ing meat, as people believed. H is work caused people t o question similar ideas. Superstitions have a strong hold on people' s imaginat ions, but they are not based on fact; t herefore, they are not scientifically valid.

The Metric System of Measurement. The met ric syst em of measurement used by scien­ tists is based on mult iples oft en. There aret wo main advantages t o t he metric system : ( 1 ) Since i t i s based o n mult iples of t en, you can easily convert to a larger or smaller unit by simply moving a decimal point . (2) The metric system is underst ood by all scientist s and is used as the syst em of measurement in most of the countries of the world.

Basic Units of the Metric System Weight - gram ( g ) Volume - liter ( L ) L ength - meter ( m )

Some Important Prefixes

centi

=

milli

=

To test hypotheses, a scientist must be able

centimeter (cm) = 1 / 1 00 of a meter

1/100

1 milliliter (m] ) = 1/1000 of a liter

1/1000

kilo = 1000

kilogram (kg ) 1000 grams

Some Important Conversion Factors 1 meter = 39.37 in . liter = 1.06 g ts. 1 kilogram = 2.2 lbs.

ml. 1 in. lb.

= = =

1 cc. 2 . 54 cm. 454 g.

Temperature Measurement FO

SCI ENTI FIC EQUIPM ENT AND M EASU REM ENT

Example

Prefix

FO

Co=

= =

( CQ X 1 . 8 ) + 32° or 9/5 Co + 32°

FO - 3 2°

_ ___

1.8

or CD

=

5/9 (FO - 32°)

3

COMMON SCIENTIFIC MEASURING INSTRUMENTS

1" ''''''''' I'':' :'':'''' l':' ' 'r'':''i

Measuring length

L

I! I

J

I

\JCC:::>I, " !

!,

0

J

Measuring diameter

Micrometer

I

I

I

!

I

!

I Measuring volume

Vernier caliper.

Measuring angles Measuring air pressure Graduated c yli nder Protractor

Bure.fte

Pipette

Measuring weight. by comparing weights of known and unknown masses

Measuring weight (Mass)

A neroid barometer

Sca re Mercury barometer

Balance

Measuring temperature Measuring nuclear radiation

Measuring electricity

Galvanometer

4

Thermometer

Geiger counter

OTHER COMMON SCIENTIFIC EQUIPMENT

� � 0 �

j

Test

Reagent bottle

tube

. Bunsen burner

Ring stand

Funnel

�

Evaporating dish

Test tube clamp

Gas collecting bottle

Tongs

u

Spatula

Tripod

Crucible

�

Watch glass

Beaker

Erlenm eyer Thistle flask tube

Florence flask

Asbestos screen Forceps

Condenser

Triangle

Mortar and pestle

'N:::;'::;'::;'::;'::;';:";:';;:';:;;"::::::::: ;:::::::::::::::::::::::::::s:· �' """""""" :.� ... ........... . .... . . .

Test tube brush

Bar magnet

Pneumatic trough

Slide rule

Medicine dropper

5

S ELF-DI SCOVERY ACTIVITY

2. Were the maggots visible in or on the jar covered with cheesecloth? ..............

.

Redi's Experiment

Let's try to verify an experiment carried out in 1668 by Redi. His hypothesis was that mag­ gots and flies do not originate from rotting meat.

3. Were the maggots visible in or on the jar covered with plastic? ...................

Materials: Three pieces of raw meat, three jars, a piece of cheesecloth, a piece of plastic, string. Conclusions:

1. What attracted the flies to the jars?

2. Why were there no maggots in the jar covered with cheesecloth? ...............

Procedure:

1. Place a piece of meat in each of the three jars.

2. Leave one jar uncovered. Tightly cover

3. Did new flies come from the raw meat?

the second jar with cheesecloth, and cover the third jar tightly with the plastic.

3. Set all t.hree jars in the open where flies can be attracted by the odor of the meat. After several days inspect the jars closely.

Observations:

1. Were the maggots visible in or on the uncovered jar? ........................

6

4. Was the belief that living things can come from non-living matter proved unscientific? ................................

.

REVIEW TESTS Completion Questions For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement. 1. Scientists have a strong

about their environment and seek to determine the

. . .. . . . . .. , answers to questions. 2. What is meant by the term "scientific method?"

3. Who can use a scientific method to obtain answers to questions? . . . .. . . . .. . ... . . .... . ...... .

4. In establishing a scientific experiment, the first step is to . . . . ... .. ... ..... .. ... . . .. . ...

.

5. Why do scientists spend so much time in the library doing research? . . ... ... . .. .. .. .. .. . .

6. What is the meaning of the term "hypothesis?" . . . . . . . . . . . . .. . .. ... .. . .. . .. . ... .. ... . .

.

7. Before carrying out an investigation, it is first essential to gather together all the . . ... .... . .. ... necessary to conduct the experimental procedures.

8. Why is it very important to keep accurate, up-to-date notes of all procedures and observations involved in a scientific experiment? . . . . . .. . . . . . . . . .. . . . . . . . .. . . . . . .. . . . . .. . .. . .. . .. .

9. What is a controlled experiment?

10.

A

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. .

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different factor introduced into an experiment is called a(an) .. .. . . .. . .. .. . .. . . . .. . . . .

11. The part of an experiment in which no new factor is introduced is called the NAME

______

CLASS,

--.JO.JDATE,

__

_______

7

12. A student set up an experiment to determine the effect of a new drug on monkeys. He kept two

monkeys under identical environmental conditions. He injected one monkey with the drug and kept accurate records for one week. Both animals were well after the experiment was finished. The student concluded that the drug was harmless to monkeys and could be safely administered to humans. List five errors in this experiment. (a)

(b)

(c)

(d)

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( e)

13. Careful collection, . . . . . . . . . . . . . . . . . . and presentation of observations are essential in an

experiment. 14. Other than for the information of their colleagues, why should scientists make their findings .

.

15. The use of scientific equipment extends man's . . . . . . . . . and increases his . . . . . . . . . . . . . . .

.

16. Why is the metric system of measurement used to such a large extent in science? . . . . .. . . .

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available to other authorities?

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17. The temperature of a solution was recorded as 200 C.

(a) Write a formula for converting Centigrade to Fahrenheit.

(b) 200 C =

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18. Body temperature is about 98.6° F.

( a ) Write a formula for converting Fahrenheit to Centigrade.

.

( b ) 98.6° F =

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, C.

19. Define the following terms: .

.

( b ) Theory: .... . ... . ... . ... .. . .. ... .... .. . . .. . . .. ..... .. . . .. ... .. . .. . ... .. . .. .

.

(c) Law:

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( a ) Fact:

20.

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. .. . .. . ... . . . .. . . . .. ... .. . ... .. ... .. . . .. . .. . . . .. . . . . .. . . ... .. . . . . . . . .

( a ) Identify the following scientific equipment: A

c

B

G

H

� . ,-

J

A:

... . . . . . ... . . ... ... .

.

D: ... ... . ... ... . ... . .. .

G: . . . . . . . . . . . . . . . . . . . . J:

. . . . . . . . . . ..........

.

=e{

B: .. . . .. . . . . . .. . . .. . .. .

E: . . . . . . . . . . .. . . . . . .. .

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C:

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F:

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I:

H: . . . . . . . . . . ... . . . . . . . .

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(b) Name the scientific instruments used to measure the following: ( 1 ) 100 em: ... . ... ................

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( 2 ) Weight, by comparing unknown and known weights: ...... ..... . .... ......... . . (3) Weight: . . . . . .. .. . . . .. .. . .... . . . . .. .. . . . . . .... .. . .. . .. .... .. . . . ..... . .. .

.

( 4 ) Air pressure: ... .... . ................ ... .... ........... .... .. ......... ...

.

( 5 ) Diameter: .... ... ...... ...... . . .. ........ ...... .... .. . . .. . . . ... ... ... ...

.

( 6 ) Volume:

.

. . . . . . . . .. . . . .. .. .. . . .. . . . . . . . . .. . .. . . . . .. . .. . .. . . . .... . .. . . . . .

( 7 ) Angles: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

( 8 ) Nuclear radiation: ..... . ... . . . . .. .. .. . .. . .. .. . .... . .. ... .. . . . .. . .. .. . .. . . .

NAME

___ ____

CLASS,

�DATE,

__

____ _ _ __

.

9

Multiple-Choice Questions In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question.

1. The basic unit of weight measurement in the metric system is the ( a ) gram, (b) kilogram, (c) centigram, (d) liter. Z. A centimeter is equal to ( a ) 1/1OOth of a meter, (b) 1/100Oth of a meter, (c) 100 meters, (d) 1000 meters. 3. Which of the following scientific instruments is used to measure air pressure? ( a ) micrometer, (b) vernier caliper, (c) burette, (d) aneroid barometer. 4. A protractor is an instrument used to measure ( a ) volume, (b) mass, (c) angles, (d ) diam­ eter. 5. The diagram below depicts a piece of scientific equipment known as a( an) ( a ) Erlenmeyer flask, (b) Florence flask, (c) beaker, (d) reagent bottle.

6. A logical guess which is sometimes used to solve a scientific problem is called (a) the scientific method, ( b ) a hypothesis, (c) a theory, (d) a law. 7. An advantage of the metric system is that ( a ) it is used in other countries such as Great Britain, ( b ) it is easier to measure with metric tools, (c) it is easier to convert to larger and smaller multiples in this system, (d) it is based on mUltiples of 5. 8. It is important in an experiment to use a sufficient number of experimental organisms to ( a ) eliminate variables that could change the results, ( b ) gain practice in the scientific method, (c) eliminate the need for a control, (d) eliminate the need to repeat the experiment. 9. How many grams in the metric system equal one pound in the English system? ( a ) 545, (b) 454, (c) 554, (d) 445. 10. A superstition is ( a ) a belief that Friday the l3th is a lucky day, (b) an unscientific conclusion, (c) a consistent observation for which there is no reasonable explanation, (d) a logical belief in the supernatural.

Matching Questi ons In the space at the left of each it,em Column B that is most closely related to that item.

Column A 1. Second step of scientific method. Z.

Only one difference.

3. Metric system. 4. One liter. S. One cc.

6. Galvanometer 7. 454 grams. 8. 1000 grams. 9. Conclusion.

Column B a. Controlled experiment b. 1000 cc c. One kilogram d. Measures electric current e. Multiples of ten f. Equal to one milliliter g. One pound h. Gather evidence i. Based on facts and evidence j. Procedure k. Variable T. Hypothesis

10. Possible solution. 10

NAME

_____ _______

CLASS

DATE

___

�

__

-----

Chapter 2

P H YSICS AN D T H E M ET R I C SYST E M The physical world, f rom the incredible sm allness of atomic structure to the extreme vastness of outer spac e, is composed of matter and energy.

Physics is the science that deals with matter and energy and their interrelationship. Matter is anything that occupies space and has mass. Mass is the quantity of matter contained in an object. Energy is the capacity or ability to do work; work - the movement of a f orce through a distance - cannot be accomplished without the exertion of energy. This energy is needed to move the f orce through a given dis­ tance. Every day p hysicists learn more about the makeup of our physical world. To organize this knowledge, physicists have devised a set of "laws" related to them. As more inf ormation is gained, these laws are revised or changed. For example, an early law of physics, stated by Aristotle, was that "the rate of f all of an ob­ ject depends upon its weight." Can you detect an error in this law? (You will learn more about it in Chapter 7 . ) We h ave accumulated so much knowledge in science that it is brok en down into many smaller areas. Each of the sciences deals with a special part of nature. Each science contributes knowledge to the others. When you study physics, you are also dealing with other sci­ ences. The th ree main branches of science are ( 1 ) physics, which deals with matter and en­ ergy, (2) chemistry, which deals with changes in matter, and (3) biology, the study of living things. The science of physics is f urther sub­ divided int o such specialized areas as biophys­ ics, geophysics, astrophysics and nuclear phys­ ics. Find out what special aspects of science physicists in these specialized areas investigate. Much scientific work is done as pure or basic science, in which the scientist searches

f or answers to questions without special inter­ est in immediate usef ul applications. Albert Einstein was a brilliant pure physi­ cist. He used mathematics to establish the f or­ mula which defines the relationship between matter and energy - E = mc2• E = energy ; m = mass; c2 = speed of light squared. Ein­ stein helped lay thef oundationf or the develop­ ment of atomic power. It is the work of the applied scientist to de­ velop usef ul applications f or the discoveries of basic research. These applications have led to the development of many new industries. These industries increase man's knowledge, improve his ability to control his environment, and add pleasure to his lif e. Examples of industries based upon the prin­ ciples of applied physics are :

Industry

Function

Machine

Design and construction of machinery

Electronics

Design and construction electronic equipment of such as radio, TV, radar, etc.

Construction

Design and construction of homes, buildings, roads, bridges, and dams

Space and Aeronantics

of

Design and construction airplanes and rockets

Metallurgy

Extraction, purification, testing and application of metals

Optics

Design and construction of instruments using lenses

11

The study of physics is usually divided into specific areas based upon the types of energy studied, such as : ( 1) mechanics, (2) electric­ ity, (3 ) light, (4) sound, (5) heat, and (6 ) nuclear energy. 1 . The Metric System. Since the science of physics uses mathematics to obtain answers to problems involving natural phenomena, it is important that you become f amiliar with the systems of measurement. There are two differ­ ent systems of measurement now used through­ out the world - the English system and the metric system. The English system did not originate in a logical, systematicf ashion; how­ ever, it is used f or everyday measurements in practically all English- speaking countries. In the English system, units of length were based upon the length of an arm or a f oot, the siz e of which, of course, varied f rom person to person. Thus, there were no constant stand­ ards. The metric system, whose origin is scientific, is used in most non-English-speaking countries and is the universal mathematical language of science. Computation in this system is simpler than in the Engl ish system . The metri c system is based upon multiples of ten, making it easy to convert f rom one unit to another. Multipli­ cation and division are done by moving the decimal point of a number. When mU ltiplying by ten or mUltiples of ten ( 100, 1000, 10,000, etc. ) the decimal point is moved to the right a number of spaces equal to the number of zeros in the multiplier. For example, if you are mul­ tiplying by 100, move the decimal point two places to the right, and so on. Examples:

( a) 45.8 X 10 = 458 ( b) 45.8 X 100 = 4580 ( c) 45.8 X 1000 = 45,800 If you are dividing a number by 10 or mul­ tiples of 10, move the decimal point to the lef t a number of spaces equal to the number of zeros in the divisor. If you are dividing by 1000, f or example, move the decimal point three places to the lef t. 12

Examples:

(a) 45.8 ---:- 10 = 4.58 (b) 45.8 ---:- 100 = .458 ( c) 45.8 ---:- 1000 = .0458 A knowledge of important prefixes will help you understand metric terms. I M PORTANT PREFIXES

Meaning

Prefix kilo (k)

1000

hecto (h)

100

deka (dk)

10

deci (d)

.1 (1/10)

centi (c)

.01 ( 1/100)

milli (m)

.001 0/1000)

Measuring in the Metric System. There are three basic quantities f or which units of meas­ urement are required : length (distance), weight (mass) and volume. These quantities are known as the fundamental units of measure­ ment because all other units are either based on them or are combinations of them. 1 . Measuring Length in the Metric System. The meter (m) is the basic unit of length in the metric system. A meter is slightly larger than one yar d and is equal to 39. 37 inches. COMMON M ETRIC UNITS OF LENGTH

kilometer (km)

=

1000 m

decameter (dkm) = 10m decimeter (dm)

= 1m

centimeter (em)

=

.

.01 m

millimeter (mm) = .001 m 2. Measuring Area in the Metric System. Area in the metric system is measured in the same manner as the English system except that metric units are used. Area is always recorded in square units.

Example:

What is the area of a rectangle 6 cm long and 5 cm wide? Area = length X width = 6 cm X 5 cm Area = 30 cm2 ( square centimeters )

SELF-DISCOVERY

ACTIVITY

Measuring Length in the Metric System.

To become familiar with metric units and the techniques of using this system of measure­ ment. Materials: Meter sti ck, graph paper, stiff paper.

Procedure: 1. Exami ne a meter stick. Note that it is divided into 100 units. Each unit, such as 1, 2, 3 and 4, represents the number of centi­ meters. Note that the meter stick is also di­ vided into groups of 10, f rom 0 to 100. You can easily see heavily printed numbers such as 10, 20, 30, etc. T he length f rom 10 to 20 represents one decimeter. T he number 30 rep­ resents 30 centimeters. T he smallest subdivi­ sion on the meter stick is the unit called a millimeter; 1000 of these tiny units are f ound on the meter stick.

2. When usi ng a meter stick you shoul d place it on its edge and avoid using the ex­ treme lef t and right edges of the scale. T hese may be ragged f rom excessive use.

dinary graph paper usually has squares 2 mm w ide and 2 mm long. Mark off the divisions in centimeters and millimeters. In order to mark the millimeters you will have to draw a line caref ully through the center of each small square, bisecting it vertically. The centimeter lines should be 6 mm high ; the half -centimeter lines should be 4 mm high; and th e millimeter lines should be 2 mm high. Cut out the com­ pleted metric ruler and paste it on a piece of stiff paper. Cut away the excess paper. 4. U se a meter stick or a metric ruler to perf orm the procedures that f ol low. Place all your answers in the accompanying chart. ( a) Draw a line 35 mm long. T his is the width of the film used in many cameras. (b) Draw a line 2 inches long and measure it to the nearest tenth of a centimeter. ( c ) Determine the number of centimeters in one inch by dividing the number of centimeters in the two-inch line by 2. ( d) Measure the width of a piece of note­ book paper to the nearest tenth of a centimeter at three different locations. Det ermine the average results to the nearest tenth of a centimeter. ( e) Measure the thickness of a dime to the nearest millimeter.

DATA CHART

( a)

3 5 mm

(b)

2"

(c) (d)

)'''''I''''''''''''''''''''''''I:::?''''''''''''� 30

1

2

3

( e)

4

3. Construct a ruler 15 cm long and 2V2 cm wide by using a sheet of graph paper. Or-

3. Measuring Volume in the Metric System. T he liter (L) is the basic unit of volume i n the metric system. A liter is slightly larger than an English quart. T he liter is equal to 1.06 quarts. 13

COMMON METRIC UNITS OF VOLUM E

kiloliter (kl)

=

dekaliter (did)

= 1 0L

deciliter (dl)

=. 1 L

centiliter (cl)

=

. 0 1L

milliliter (ml)

=

. 00 1 L

1 000L

MENISCUS -

Reading a graduated cylinder.

SELF-DISCOVERY ACTIVITY

cubic centimeter (cc) = .00 1 L Measuring the volume of a solid in the met­ ric system is the same as the method used in the English system . Volume is always recorded in cubic units. Example:

Measuring Volume in the Metric System.

Materials: Water, graduated cylinder, thread, object whose volume is to be determined.

What is the volume of a box 60 cm long, 30 e m wide and 1 0 cm high? Volume = length X width X height = 60 cm X 30 cm X 1 0 cm Volume = 1 8,000 cm3 or = 18,000 cc ( cubic centimeters )

Procedure and Conclusions:

The volume of a liquid is also measured in cubic units. A graduated cylinder is of ten used to obtain accurate volumetric measurements. The surf ace of the liquid is curved slightly since the liquid either f alls or rises where it touches the wall of the container. This curved surf ace is called the meniscus. Always take the reading at eye level, reading the top of the meniscus if the surf ace curves upward and the bottom of the meniscus if the surf ace curves downward.

measure its volume . . . . . . . . . . . . . . . . . . mI.

G R A M 5

�eC/ci/n.j:

Determine the volume of any irregular ob­ ject that will fit into a 1 00 ml graduated cylin­ der by perf orming the f ollowing proced ures: 1. Pour some water into the cylinder and

2. Tie a piece of thread around the object and lower it into the cylinder. 3. Measure the new total volume. . . . . . . ml. 4. Determine the volume of the irregular object by subtracting the initial total volume f rom the final total volume. Volume of the ir-

regular object . . . . . . . . .. . . . . ml.

G R A M 5

T56.8qrams

The scales of a metric balance. 14

4. Measuring Weight in the Metric System.

The gram (g) is the basic unit of weight ( mass) in the metric system. One pound is equal to approximately 454 grams.

SELF-DISCOVERY ACTIVITY Weighing in the Metric System.

Materials: A penny, pencil, 1 50 ml beaker, water, balance.

COMMON M ETRIC UNITS OF WEIGHT

kilogram or kilo (kg)= 1 000 g

Procedure:

dekagram (dkg)

Following the weighing procedure outlined on pages 1 3 , 1 4, weigh each of the obj ects listed in the Data Chart below, using the balance. Record the weight of each in the space provided.

=

10 g

decigram (dg)

= .1 g

centigram (cg)

= .01 g

milligram (mg)

=

.00 1 g

DATA CHART

The balance is a scientific instrument which can be used to determine the metric weight of an object. The accompanying diagram shows the scales of a typical metric balance. The upper scale is divided in to decagrams; the center scale is divided into 1 00-gram sections ; and the lower scale into grams and decigrams. B y moving the sliding weights attached to eac h sc ale, we are able to balance an object that has been placed in the weighing pan. When the object has been balanced, we can determine its weight by totaling the number of grams indicated by the positions of the slides on eac h scale. In the diagram, for exam­ ple, there is a reading of 50 grams on the up­ per sc ale, 1 00 grams on the center scale and 6 . 8 grams on the lower scale. Together they total 1 5 6 . 8 grams and indic ate the wej ght of the object being weighed.

Weight

Object penny penc il 1 50 ml b eaker 1 50 ml beaker

+ 1 00 ml water . . . . . . . . . . . . . . . . . . . . . .

.

1 00 ml water 1 ml water 1 L water 5. Conversion Factors. Many times it is necessary to co nvert from the metric system to the English system and from the English sys­ tem to the metric system. In order to do this, the following conversion factors are used:

CONVERSION FACTORS

Length 1 m

=

39.37 in

2 .54 cm= 1 in 1 km

= .62 mi

Volume 1 L = 1 .06 qts 1 L= 1 000 ml or 1 000 cc 1 ml= 1 cc

Weight 1 kg= 2.2 lbs 454 g =1 lb 28.3 g

= 1 oz

15

C O M M O N METRIC UN ITS

i,""'I� 0 I � . ' ' II il ij i � � 1 il�LIJ J Length

Volume - solids

1

1 cm.

.

�

\ �<$-'

1

.

I

I

I

I

I

I

cu. cm.

..

I

J

39.37 in.

in.

.

2.5 cm.

J

I

.

Distance

) PAR�

-1 km.

1 m.

=

.6rV

(1 cm' or 1 cc.l

Volume - liquids

Q

� -

Weight

-

-

3=

-

-

2=

-

1

ml.

./ 1

16

-

--

ml.

=

GRAMS cc.

::::.. 1 cc.

2.2Ibs.

1 liter.

�l

If"

REVIEW TESTS Completion Questions For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement.

1. What is the meaning of the term "physics?" . . .. . . . . . . . . . . . . . . . . . . . . . . . . . .. . ... .. . .. . . .

2. A biophysicist specializes in

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3. Define the following in metric system units: ( a ) decimeter:

(d) kilogram:

( b ) milligram:

( e ) centimeter:

(c)

kilometer:

4. Complete the following by placing the correct answer in the blank provided: (a) 2000 ml =

. . .. L

.

(d) 1 4 cm

=

.

. ..

.

( g ) 1 2 cm =

m

.

( b ) 6.5 cm

mm

( e ) 6 8 km =

m

( h ) .4 g

(c) 8 m

mm

(f) 200 cc

ml

(i)

=

.

.

.

"

dm

- . .."

cg

13 m

km

5. Find the total of the following in meters: 4 km, 3 cm, 5 mm, 8 dm, 2 m . . . . . . . . . .. . . m. 6. If you were 5 feet 2 inches tall, how many meters tall would you be? . . . ... ... .... m. 7. A pencil is 5 inches long. Its length in centimeters is ... . . . . . . . . cm. 8. Five kilograms equal ... . pounds. 9. Six inches equal . . . . . . cm or

mm.

10. Two and one-half pounds equal

grams.

11. A liter of water is equal to . .. . . m!. 12. A one-gallon container will hold about . . . .. . liters. 13. 6.57 yards equals . . . . . . . . . in. ; 14. What is the area of a board 2 m long and 90 cm wide? . . .. . . .. . .... . ...... .. . .. .. . .. . .

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15. What is the volume of a box having the following dimensions? 6 m X 8 NAME·

_______

CLASS,

DATE

___

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m

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.'

X 8 0 cm

________

17

Multiple-Choice Q uestions

In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question. 1. Matter will always have ( a ) solid form, ( b ) weight, (c) life, (d) mass. 2. A search for the truth, with no demand for immediate practical application of this knowledge, would best describe the goals of (a) physical science, ( b ) pure science, (c) applied science, (4) natural science. 3. Study of the physical laws relating to the structure and activity of the earth is called (a) nuclear physics, ( b ) optical physics, ( c ) geophysics, (d) astrophysics. 4. An industry based upon the principles of applied physics that deals with the refining of iron ore is ( a) metallurgy, ( b ) optics, ( c ) aeronautics, (d) construction. 5. The metric system is based upon multiples of ( a) 1 0, ( b ) 1 00, (c) 1 000, (d) 1 0,000. 6. 227 grams is equal to about ( a ) l ib,

( b ) Ih lb, (c) 2 lbs, ( d) Ph lbs.

7. The basic unit of volume in the metric system is the ( a ) meter, ( b ) liter, ( c ) gram, (d) cubic centimeter. 8. Which of the following is the largest unit? (a) dekagram, ( b ) decigram, ( c ) milligram, (d) kilo­ gram. 9. The distance from a certain town to Rome is 8 kilometers. This is equal to about (a) 5 miles, ( b ) 2 miles, ( c ) Yz mile, (d) 48 miles.

10. A liter is slightly larger than a ( an )

( a ) ounce, ( b ) pint, ( c ) quart, (d) gallon.

Match ing Questions

In the space at the left of each item in Column A, place the letter of the term or expression in Column B that is most closely related to that item. Column B

Column A a. b. c. d. e.

Metric system Nuclear physics Meniscus Aeronautics Matter-energy formula f. English system g. Cm h. Mm 1. Applied science j. Weight k. Volume I. Mass m. Albert Einstein n. Area o. Albert Schweitzer

1. Physical laws relating to atomic structure 2. Famous physicist 3. Principles of physics applied to an industry 4. E

=

mc2

6. Curved surface of a liquid

7. Useful application of scientific knowledge 8. Smallest unit on a meter stick 9. Always a property of matter

10. Scientific system of measurement

18

NAME

______

CLASS

D �ATE

__ __ __

_ __ __ __ __ __ __ __

Chapter 3

FORCES

What i s a force? I t i s any push or pull which can produce, prevent or stop motion. As you walk down the street, the force of gravity is pulling you toward the center of the earth. The force of friction of the air blowing against you may tend to slow you down. As you turn a corner, you are affected by the force of inertia, which tends to keep something moving in the same direction. All this time your body is held together by molecular forces. These four forces : gravity, friction, inertia, and molecular will be studied in this chapter. Gravitational Force. The force of gravity is responsible for weight. Weight is a measure of the gravitational pull of a body upon a mass. If you weigh 1 35 pounds, you are being pulled toward the center of the earth with a force of I 35 pounds. Mass is the amount of matter a body con­ tains. Mass never changes, no matter where it is. Weight, however, varies, depending upon the mass of the object and its distance from the center of gravitational force. The greater the mass of an object, the greater is its weight. The farther an object is from the center of a: planet, the less it will weigh. The earth is not a perfect sphere-it is flat­ ter at the poles than it is at the equator. Since the poles are closer to the center of gravity than the equator, an object weighing 1 8 9 pounds at the equator will weigh about 1 90 pounds at the poles. If the pull of gravity is counterbalanced or equalled by an opposing force, the object will be weightless. Space ships revolving around an object in orbit become weightless when their speed of revolution equals the pull of gravity on the object. The weight of an object can be determined with a spring scale or by comparing the weight

of an unknown mass with a known standard on a very sensitive balance.

The Law of Gravitational Attraction. Sir Isaac Newton, the great English scientist, developed the Law of Universal Gravitation. According to this law, all bodies in the universe . attract each other with a force that ( a ) is directly pro­ portional to their masses, and ( b ) is inversely proportional to the square of the distance be­ tween them ( J" ) . Newton discovered that when the distance between the masses does not change, then doubling their masses will double their weight. If the masses remain the same, then doubling the distance between them will reduce their weight by one-fourth. Tripling the distance between them will reduce their weight by one-ninth, as shown:

Example:

1 _ � (3) 2 - 9

A boy weighs 1 5 6 pounds on the surface of the earth. If his distance from the center of gravity were doubled, he would weigh only one-fourth this weight, or 39 pounds.

SELF-DISCOVERY ACTIVITY To Determine the Center of Gravity of an Irregular Object.

Materials: B oard, nail, plumb line, eraser, pencil, thumb tack.

Procedure: 1 . Cut a board in the shape of an irregular polygon and drill three holes near different edges as shown in the diagram. 19

2. Hang the polygon on a nail by passing the nail through one of the holes. 3. The polygon will take a position with its center of gravity below the nail. 4. Drop a plumb line from the nail and

draw the position of this line on the polygon directly behind the string. 5. Repeat this procedure, using each of the other two holes.

6. The point where the three lines intersect represents the center of gravity of the irregular polygon.

ciency of machines. Cooling systems that use water, oil or air remove the excessive heat. SELF-DISCOVERY ACTIVITY Exploring the Force of Friction.

Materials: Cord, book, spring scale.

Procedure: Attach a cord around a book as shown in the diagram. Attach the spring scale to the cord. Applying a constant pull to the spring scale, obtain several readings of the force nec­ essary to start the book in motion.

7. Place a thumb tack in the end of a pen­ cil eraser and try to balance the polygon on it

at its center of gravity. Observation: . . . . . . . .

Force necessary to overcome starting friction.

Observations: 1 . Record your results.

2. Compare the magnitude of the applied The Force of Friction. The force which resists sliding or rolling motion by opposing the movement of one body over or through an­ other is called friction. It can be either useful or harmful. 1. Useful Friction. Without friction we could not walk or stop machines, bicycles or automobiles. The automobile stops when we step on the brakes. Frictional force between the tires and the road puts the car in motion. The force of friction is reduced by rain, snow and ice. Friction between a meteor and the molecules in our atmosphere cause most me­ teors from outer space to burn up before they reach earth. 2. Harmful Friction. Every time we try to push or pull something, the force of friction opposes us. Friction causes moving parts of a machine to wear out. Lubricants, bearings and smooth surfaces reduce this harmful force. Heat, caused by friction, reduces the effi20

force to the weight of the book. Results: . . .

3. Explain the results obtained in question (2).

4. Place the book on its end and record the force necessary to start it in motion. Re-

sults: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Y.--�) Force necessary to overcome starting friction.

What do you conclude by comparing the results of the force required to put the book in motion when placed fiat on the table and when placed on edge? . . . . . . . . . . . . . . . . . . . . . .

7. Determine the magnitude of the force applied to the book without pencils, after an­ other book has been placed on top of it. The force should be determined after the book is in motion.

±:-:.:-:-:.:-:-:.:-:-:-:-:.�.:.:L � ., /':':':':':':':':':':':':':'

5. Determine the magnitude of the force required to keep the book moving after it is already in motion.

Applied force . . . . . . . . . . . . . . . . . . . . . . .

What is the relationship between the fric­ tional force and the force pressing the two Force necessary to overcome sliding friction.

Applied force . . . . . . . . . . . .. . . . . . . . . .

.

What do you conclude after comparing starting friction to sliding friction? . . . . . . . . .

6. Determine the magnitude of the ap­ plied force needed to keep the book in motion after two or three pencils are placed below the book, and record the results.

Applied force . . . . . . . . . . . . . . . . . . . . . .

books together?

The Force of Inertia. Have you ever wondered why a satellite stays in an orbit around the earth? This is caused by an interaction of two forces, gravity and inertia. Inertia is a force, not well understood by scientists, that tends to keep something moving in a straight line. As a satellite moves in space at many thousands of miles per hour, the force of inertia tends to keep it moving in a straight line past the earth. ( This force of inertia is often called centrifugal force. )

.

Sa tellite in orbit.

Compare the use of pencils in the above case with the use of machine ball bearings.

F, F.

= =

gravitational force inertial force

However, the force of gravity is pulling the satellite constantly toward the earth. If the two forces are in balance, the satellite will re­ main in orbit until the force of friction of tiny particles in space slows it down. Then, it plum­ mets to earth and burns from the heat of the force of friction as it moves through the dense 21

atmosphere. Under what circumstances could the force of inertia be so great that the satellite is lost in space? . . . . . . . . . . . . . . . . . . . . . . . The next time you are riding in an auto­ mobile that turns a corner, notice the inertial force. Also when you are running in a game of baseball, why is it hard to turn at bases? . . . . .

What force helps you turn in the car and when running? Can you guess? Here's a clue. What about cars that try to turn sharp curves when it is raining? What about turning the bases when the field is muddy?

Molecular Forces. The attractive forces be­ tween molecules are responsible for cohesion, surface tension, adhesion and capillary action. Cohesion is the force of attraction between like molecules. It is this force that holds matter to­ gether. If it were not for the force of cohesion all materials would fly apart and become gas. Cohesion is responsible for surface tension.

' 1 e tc ( �

GYRO·COMPASS USED IN GUIDANCE SYSTEMS

CENTRIFUGE

Useful applica tions of inertial force.

It is surface tension that causes the surface of a liquid to act as if it were a thin plastic membrane, a "skin." The surface molecules of the liquid are attracted downward by the co­ hesive forces of molecules below them. It is this surface tension that enables you to blow soap bubbles, or enables a water insect to glide across a pond. Surface tension also enables a razor blade to float on water. Adhesion is the attractive force between dif­ ferent kinds of molecules. The action of glue and other adhesives is based upon adhesion. 22

Capillary action i s dependent upon adhesive forces. This is the attraction of the walls of a thin tube for the liquid within. Capillary action causes the liquid to creep up the tube, form­ ing a curved surface called a meniscus at its surface. If the cohesive force of the mole­ cules within the liquid is stronger than the ad­ hesive forces, the liquid will curve downward, as in the case of mercury. Capillary action helps to carry soil water from the roots of a plant up to the stem and leaves. It also makes a paper towel or a blotter absorb liquids.

Cohesion

A dhesion

Attraction between like and unlike molecules.

�� f�

GLU ING WOOD CAPILLARY

SPIDER BLADE

Effects of surface tension. Effects of adhesion.

Force Vectors. In measuring quantities such as length, area, volume, mass, density, time, and age we need only consider one characteristic - magnitude. Magnitude may represent the size or amount of the quantity being measured. Quantities possessing only magnitude are called scalar quantities. Forces, however, must be described by two important characteristics: ( a ) magnitude, and ( b ) direction. Forces can be illustrated vis­ ually by an arrow called a vector. The arrow­ head always represents the direction of the force acting upon an object; the tail shows the point where the force is applied. The length of the arrow indicates the magnitude or size of the force. A suitable scale must be selected to determine the length of the arrow, such as 1 cm. = I lb. of force, or 1 /4 in. = 1 lb. of force. 1 cm. ) 5 lbs. 1 lb .

Concurrent Forces. When two or more forces are acting on an object at the same time they are called concurrent forces. If no unbalanced force acts on an object, the object is said to be in a state of equilibrium. 10 LBS.

finding the square root of the sum of the squares of the applied forces.

R = yFi + F; Example:

What would be the resultant of a force of 3 pounds and a force of 4 pounds acting at right angles to each other?

10 LBS.

R = vFi + F� R = y32 + 42 R = y9 + 1 6

Balanced concurrent forces producing equilibrium.

If two or more forces were acting upon the same point, they could be replaced by a single force which would produce the same effect. This single force is called the resultant. If the original forces were acting in the same direction, the resultant would be equal to the sum of the two forces. Example:

The resultant of two forces of 5 pounds and 1 0 pounds, acting in the same direction is equal to 1 5 pounds. w

.�---------�--------�.

5 lbs.

E

1 0 1bs.

Resultant

=

1 5 lbs. East

If the forces were acting in opposite direc­ tions, the resultant would be equal to the arith­ metic difference of the applied forces and would be in the direction of the larger force. Example:

R = y25 R

=

5

lbs

The magnitude of the resultant can be ob­ tained by drawing the applied forces to scale and completing the parallelogram with the two forces acting at the given angle as sides. Draw in the diagonal as shown by the dotted line in the above diagram. Measurement of the diagonal gives the magnitude of the resultant. If the concurrent forces (forces acting si­ multaneously ) act at an angle other than a right angle, the approximate value of the resultant can be obtained. We can construct a parallelogram to scale using the two vectors as the sides of the parallelogram. A protractor is used to draw the correct angle between the forces. Measurement of the diagonal of the parallelogram will give the approximate mag­ nitude of the resultant as shown by the follow­ ing diagram. Increasing the angle between the applied forces reduces the magnitude of the resultant.

If a force of 1 0 pounds were directed east and a force of 5 pounds directed west, the re­ sultant would be 5 pounds directed east. W

.,--------.--------�.

5

E

lbs.

1 0 lbs . •I------� E Resultant = 5 lbs. East If the two forces were acting at right angles to each other, the resultant is determined by

Effect of concurrent forces acting at an angle other than 90° . 23

The equilibrant is a single force equal but opposite in direction to the resultant. The equilibrant can prevent motion on the part of the object to which the forces are applied. Any single force acting on an object can be considered to be the resultant of two or more concurrent forces. These concurrent forces

Materials: Cord, book, two scales.

Procedure: 1. Place two cords around the book and attach a scale to each cord, as shown in the diagram. Apply two forces by pulling on both scales with a constant motion.

2. Record the magnitude of each applied

.... z:

< en a:: == I::t:I

�

::> d ....

C> ...

The equilibrant is equal but opposite to the resultant.

are called the components of the original force. For example, when a boy pulls a wagon he exerts a force on the handle. The two com­ ponents of this single force are ( a) a vertical component which counteracts gravity, and ( b ) a horizontal component that actually performs the useful work of pulling the wagon forward. Finding the components of a single force is called the resolution of a force. F A

=

Horizontal component which

B

=

Vertical component which

=

force. Scale 1

. . .

. .

.

.

.

.

Scale

2........

.

3. What is the magnitude of the resultant? 4. What would be the magnitude and the direction of the equilibrant force needed to

prevent motion? . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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5. Determine the magnitude of the result­ ant by applying two forces at right angles to each other. - ATTACH TO HOOK IN WALL

Single applied force on handle. pulls the wagon forward.

FORCE 1

counteracts gravity.

Concurrent forces acting at right angles to each other.

1. ' " 2. . . . . . . . . . . . . .

6. Record the magnitude of force ·

SELF-D I SCOVERY ACTIVITY

Investigating Resultant and Equilibrant forces. 24

. . .

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. . . . .

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. . Force

7. The resultant is equal to a force of "

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R EVI EW T ESTS Completion Questions

For each of the statements or questions below, write the word or phrase in the space best answers the question or completes the statement.

provided that

1. What is the meaning of each of the following terms? .

( a) Force :

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( b ) Weight :

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( c ) Mass : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. As an object is moved from the equator to the north pole its weight will . . . . . . . . . . . . . . . . . . . 3. What does the Law of Gravitation state? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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4. The force of one object upon another is directly proportional to the product of their S. Describe three ways in which the force of friction is useful.

(a) (b)

(c) 6. Attempting to stop a car o n an icy pavement i s difficult because the force o f . . . . . . . . . . . . . is greatly reduced. 7. The efficiency of a machine is greatly reduced by friction which wears its parts and converts much of its energy into undesirable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.

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. . . force tends to draw an orbiting satellite back toward the center of the earth.

9. If it were not for . . . . . . . . . . . . . . . . force an orbiting satellite would be flung into outer space

by . . . . . . . . . . . . . . . . force. 10. The apparent force acting upon a person in a car traveling around a curve is sometimes called . . . . force.

NAME

_____ _____

CLASS.

DATE

___

_ _ _ _ _ _ _ _

25

11. List three devices which make use of a gyroscope. (a) (b) ( c)

12. What is the meaning of each of the following terms? (a) Cohesion: ( b ) Adhesion : (c) Surface tension :

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13. Surface tension is caused by a . . . . . . . . . . . . . . . . . . . . attraction of surface molecules by strong cohesive forces. 14. A meniscus forming an upward curvature in a liquid is caused by . . . . . . . . . . . forces. 15. Three parallel forces are acting simultaneously at the same point on an object. One force is pulling to the left with a force of 25 lbs. and the other two are pulling to the right with forces of 10 lbs. and 5 lbs. respectively. (a) Graphically represent these forces by using the following scale. Scale :

1 inch 10 lbs.

( b ) The magnitude and the direction of the resultant of the applied forces is . . . . . . . . . . . . . .

.

16. If the difference between all forces acting at a point is zero, the forces are in . . . . . . . . . . . . . . . . . . .

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17. The

. . . . . . . . . . . . . . . . is a single force which can balance two opposing forces to prevent

motion. 18. A boy pushes a lawnmower with a force of 25 lbs. at an angle of 30° from the ground. In the space below, draw a vector diagram to determine the force pushing the lawn mower into the ground. Use a scale of 1 inch = 10 lbs. (a) Label the length and force of the horizontal and vertical components, as well as their resultant. ( b ) Label the component providing the for­ ward push and the component providing the downward push. 19. As the angle between two concurrent forces increases, the magnitude of the resultant . . . .

26

NAME ______ CLASS

D � ATE

__ __ __

__ __ __ __ __ __ __ _

20. As a result of a series of experiments involving friction, the following data regarding the applied forces were collected. Use the graph paper to construct a bar graph using this data and your knowledge of frictional forces. There is no specific order to the data listed. Applied forces to overcome the force of friction : 250 grams, 1 60 grams, 230 grams, 1 75 grams, 1 40 grams. OVERCOMING FRICTION

260 250 240 230 220 210

KEY A

=

Starting friction, rough surface

B

=

Starting friction, smooth surface

C

=

Sliding friction, smooth surface

D = Sliding friction, rough surface

+ rollers

E

=

en :::E c

... ...

200

:!: 1 90

... c.:o ... co .... CI ... :::;

aac

Starting friction, rough surface + added weight.

1 80 1 70 1 60 1 50 1 40 1 30 1 20 110 1 00 A

B

C

E

0

Mu ltiple-Choice Questions

In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question. 1. Which of the following represents a scalar quantity? (d) water pressure.

(a) friction,

( b ) weight,

( c ) length,

2. Roads are banked to prevent vehicles from leaving the road because of (a) gravity, ( b ) friction, (c) centripetal force, (d) inertial force. 3. The magnitude of the resultant of a force pulling on an object toward the west with a force of 20 Ibs. and another force pulling the object east with a force of 60 lbs. is ( a ) 80 lbs. east, ( b ) 40 lbs. west, (c) 40 lbs. east, (d) 80 lbs. west. NAME

______

CLASS,

-L..t DATE

__

_ _ _ _ _ _ _

27

4. As a rocket is hurled into space, which of the following properties will remain constant? (a) mass, (b) weight, ( c ) velocity, (d) temperature. S. The attractive force between similar molecules is an example of

(a) adhesion,

(b) cohesion,

( c ) capillary action, (d) surface tension.

6. An arrow used to illustrate the size and direction of a force is called a ( an ) ( b ) vector, ( c ) equilibrant, (d) component.

(a) resultant,

7. The resultant of two parallel forces of 50 lbs. each acting in opposite directions on a 75 lb. box lying on a fiat surface, would be ( a ) 50 1bs., ( b ) 75 Ibs. , ( c ) 1 25 lbs. , (d) O lbs. 8. A man weighed 1 7 1 lbs. on the surface of the earth. If his distance from the center of the earth were tripled, he would weigh ( a ) 1 7 1 Ibs . , ( b ) 90 Ibs ., (c) 1 9 Ibs ., (d) 43 1bs. 9. Soil water reaches the stem and leaves of a plant with the help of (a) gravity, ( b ) capillary action, ( c ) centrifugal force, (d) surface tension. 10. The force responsible for surface tension is (d) adhesion.

( a ) cohesion,

( b ) gravity,

( c ) water pressure,

Matching Q uestions In the space at the left of each item in Column A, place the letter of the term or expression in Column B that is most closely related to that item.

Column B

Column A a. b. c. d. e. f.

1. Law of Gravitation 2. Point at which all of the weight of a mass seems to be concentrated 3. Causes the destruction of meteors

Gyroscope Atmospheric friction Centripetal force Weightless object Sir Isaac Newton

vF� + F� g. Inertial force

4. Keeps an object moving in a straight line S. Gravitational force = Inertial force

h. Center of gravity Has magnitude and direction j. Gluing objects together k. Concurrent forces I. Cohesive forces m. Scalar quantity i.

6. Object that resists a change in direction 7. Force of a growing root 8. Two or more forces acting on an object at the same time 9. Adhesive forces 10. Attractive forces between iron molecules

28

NAM E_______ CLASS

DATE

____

_ _ _ _ _ _ __

Chapter 4

FORC ES A N D WO R K E N ERGY A N D WORK

What Is Energy? Energy is defined as the ability to do work. Without energy, work cannot be accomplished. Thus, when we say that something has energy, we mean that it is capable of exerting a force on something else and performing work on it. Energy is present in all matter and can be changed from one form into another - but it cannot be destroyed. Until recently, physicists thought that energy also could not be created. How­ ever, in a thermonuclear reaction, such as a hydrogen bomb, energy appears to be created directly from matter. For this reason, most physicists now support the idea that matter and energy are different forms of the same thing. Energy may take on many forms , some of which are mechanical, electrical, chemical, heat, sound, light and nuclear energy. Potential Energy. This kind of energy is in­ active, but is ready to be used. The energy stored in an object or the energy an object possesses because of its position or condition is known as potential energy. For examples of potential energy, just picture a coiled spring, a stick of dynamite, a fully charged, unused battery, water behind a dam, a rock sitting on top of a cliff and the tremendous energy locked up inside an atom. Kinetic Energy. The energy an object pos­ sesses because of its motion is called kinetic energy. The word kinetic means "moving." Kinetic energy i s a form o f energy i n motion; it is active. Let's go back to the examples of potential energy. The coiled spring unwinds, the dyna­ mite explodes, the water behind the dam is released, the rock topples off the cliff, and the atom is split apart. In each of these

examples the object is active - it is now moving. Imagine a rocket standing on its launch pad ready for blast off. Its huge cylinders are filled with fuel which possesses potential en­ ergy. With a tremendous roar, the rocket lifts off the pad and hurtles into outer space. The rocket no longer possesses the potential en­ ergy of its fuel ; it now has kinetic energy due to its motion.

What Is Work? You would probably answer this question in several ways. Mowing the lawn, babysitting, carrying things, digging, pulling weeds, and homework assignments may all be defined as work in the usual sense. How­ ever, scientists have a scientific definition for the term work just as they have for force and energy. Scientists define work as the result of the exertion of a force through a certain dis­ tance to overcome a resistance. Summarizing, we can say that scientifically, in order to do work, ( 1 ) a force must be applied to an object, ( 2 ) a resistance must be overcome, and (3) the applied force must move the object a cer-' tain distance. In the case of the rocket, for example, the chemical energy of the burning fuel produced a force which could overcome the resistance of gravity and lift the rocket off the ground. Four major types of resistance are met in doing work : ( 1 ) gravity, in lifting objects, ( 2 ) friction, in sliding one object over an­ other, ( 3 ) molecular attraction, in cutting, bending or heating objects, and ( 4 ) inertia. Friction is defined as the resistance of one body to the movement of another body along its surface. Inertia is the tendency of an object to re­ main at rest or in motion due to its mass. The greater the mass of an object, the greater its inertia. 29

Inertia must be overcome, for example, in first putting an object in motion or stopping it once it is in motion. The property of inertia explains why the force needed to overcome starting friction is more than sliding friction. It also explains why a person on a bus lurches forward after the bus has stopped. The amount of work done can be found by multiplying the force (F) by the distance (D) it moves an object: w

F

Work

D

X

Force

Distance

The distance moved must be in the direc­ tion of the applied force. Work is usually measured in foot-pounds (ft.-lb. ) when F is expressed in pounds and D in feet. A foot­ pound is the work done by a one-pound force moving an object a distance of one foot.

Since the force applied in lifting the box was upward, opposing the force of gravity, work was done. On the other hand, the force exerted in carrying the box, after it had been lifted, was not in the direction of the applied force but perpendicular to it so that no work was done on the box.

What Is Power? Power is a measure of the rate at which work is done. In determining power, two factors must be taken into con­ sideration : ( 1 ) work, and ( 2 ) time. Suppose a trench can be dug by one man in 1 0 days, or by two men in 5 days, or by a trench-digging machine in one day. In all three cases, the amount of work done is the same. However, the power used in each of the three instances is quite different. What was the power of the machine as compared to that of one man? . . . . . . . . . . . . . . . . . . . . . . . . . . .

Example:

.

If you lift a box weighing 60 pounds through a distance of 5 feet, how much work do you do? Power can be expressed mathematically according to the following formula :

W= F X D = 60 lb. X 5 ft. 300 ft.-lb. =

After lifting the box, you carry the box a distance of 1 5 feet, and place it on a truck. How much work was done on the box? You may be surprised to learn that the answer is zero! Reread the definition of work on page 29 carefully. Do you see that work is accomplished only if the distance the object moves is in the direction of the applied force?

.?Dr"I",:',:." 'J

5 ft.

t

"

:zJ1®i. �

:-:.;.:�-::

"Iff};

� - -----------------------� � Walking with the box. Lifting the box.

W= F X D = 60 lb. X 5 ft. 300 ft.-lb. =

30

I.

W=F = 60

XD X 0

lb. Distance not in direc­ tion of applied force.

Power

=

Work Time

=

Force

X

Distance

Time

=

FXD T Power is expressed in foot-pounds per sec­ ond (ft.-lb. jsec. ) and foot-pounds per minute (ft.-lb. jmin. ) . Example:

in

If a man performed 1 0,000 ft.-lb. of work 5 minutes, how much power did he produce?

P

=

1 0,000 ft.-lb. = 2 , 000 5 min.

ft .-lb. /mm. .

Horsepower. The power developed by rna· chines is usually measured in units called horsepower (HP). In order to produce 1 HP, 33,000 ft.-lb. of work must be done in 1 minute, or 550 ft.-lb. in 1 second. The fol­ lowing formulas are used to calculate the horsepower rating of an engine or machine.

( a ) HP = F

W

_ _ _ __ _

T ( min. ) X

33,000

T ( min. ) X

( b ) HP = F

33,000

D

X

W

_ _ _ _

T ( sec. ) X

550

X D

T ( sec. ) X

550

Example: A mass weighing 660 pounds was lifted a distance of 600 feet in 3 minutes. How much horsepower was developed by the machine which did this job?

( a ) HP =

660 lb. X 600 ft. 3 min. X 3 3,000 396,000 99,000

= 4 HP or ( b ) HP

=

660 lb. X 600 ft. 1 80 sec. X 550 396,000 99,000

= 4 HP

cannot produce more energy or work than what is put into it. The Law of Machines states that under ideal conditions, the work output of any ma­ chine must theoretically equal the work input. A machine, therefore, can never multiply work. Not only is it impossible for a machine to multiply work, it is also impossible for the work output to equal the work input. The Law of Machines is theoretical because it does not take into account the force of friction which is always present" In fact, the efficiency of a machine is always less than 1 00 % , indicating that the amount of work input is always greater than the work output. Efficiency, therefore, is the ratio of the output of useful work to the total work input ex­ pressed as a per cent. Efficiency in %

=

Work Output Work Input

X

1 00 %

Example: What is the efficiency of a machine in which in and

2500 ft.-lb. of work has been put 500 ft.-lb. of work put out? . 500 ft.-lb. Efficlency = X 1 00% 2500 ft.-lb. 0

Efficiency

=

20 %

Machines. A machine enables us to do work more easily or more quickly. Using a ma­ chine, we need to apply only a small force to overcome a large resistance or reduce the time necessary to do work. Some machines can also change one form of energy into another. Electric motors, for example, transform electrical energy into me­ chanical energy. Generators, on the other hand, convert mechanical energy into electri­ cal energy. The chemical energy locked up in fuels such as gasoline or oil may be changed into mechanical or heat energy by automotive engines.

Machines are either simple or compound, depending upon how complex they are. There are six simple machines having only one or few parts. These simple machines include the ( l ) lever, ( 2 ) inclined plane, ( 3 ) wedge, ( 4 ) screw, ( 5 ) pulley, and the ( 6 ) wheel and axle. Compound machines are made up of two or more simple machines which together do a specific job.

The Law of Machines. According to the Law of Conservation of Energy, energy may be changed from one form to another, but it cannot be created or destroyed by usual means. Therefore, under normal conditions, a machine

The Lever. A lever is a rigid bar supported at a point around which the lever can turn. The lever was probably discovered by early man when he learned to use a long pole or bar to move a rock or log. The two parts of the

SIMPL E AND COMPOUND MAC H I NES

31

lever were easy to obtain, and probably made the first machine known to man. To understand better how a lever works sci­ entifically, we must first study its parts : ( 1 ) The fulcrum is the pivot point on which the lever bar is supported. This may be a rock, a brick, or a specially designed part. (2) The effort arm of the lever bar is the part on the side of the fulcrum where an effort or force is being applied. ( 3 ) The resistance arm of the lever bar is the part of the bar that resists the applied force. In doing work with a lever, force is ap­ plied . to the effort arm to overcome the resis­ tance at the end of the resistance arm so that there is movement. Force or effort is abbrevi­ ated ( E ) ; effort arm ( EA ) ; resistance arm (RA) ; resistance (R) ; and fulcrum ( F ) .

�

$

These factors are illustrated in the following diagram of the lever :

E "_<===�_E_A�����_+�_i :====�_R_A �!+

_

_

F

The lever - a simple machine.

Classes of Levers. Levers are grouped into three classes, depending upon the relative posi­ tions of the effort, fulcrum and resistance. These classes are known as the ( 1 ) first-class lever, ( 2 ) the second-class lever, and (3 ) the third-class lever.

either the force or the distance and speed ­ but not all at the same time. In order to gain force, speed or distance must be sacrificed. To gain distance or speed, force must be sacri­ ficed. In order to increase jorce, using a first­ class lever, the effort arm must be longer than the resistance arm .

Ebl-Oo(F-----EA

t

----->-� i�

i �

RA �

m t

F

First-class lever used to increase force.

Since it multiplies the force put in, a first­ class lever allows us to exert a smaller force to overcome a resistance. However, to obtain this increased force, we must increase the distance through which the effort is applied.

E I'�

G D

�/

/�/�;� / F / 1"-?.f.

Applications of the first-class lever used to increase force.

Thus, in a first-class lever, the distance through which the effort must be applied is always larger than the distance through which the resistance is moved.

1. First-Class Levers. In the first-class lever the resistance is at one end, the effort at the other. The fulcrum is located somewhere be­ tween the effort and the resistance.

E ,,,,,(�-- EA tJf======= RA :;:::R :J = �= Ql == == ==ir= =;; == �l

I

-----

• F

----'��I

'f'

First-class lever.

A first-class lever always changes the direc­ tion of the applied force. It may also increase 32

Increasing force by sacrificing distance.

To increase distance and speed, using a first-class lever, the resistance arm must al­ ways be longer than the effort arm.

E

RA ----� �

I I I

t Barber's or tailor's shears used to increase distance or speed.

2. Second·Class Levers. In the second-class lever, the fulcrum and effort are on opposite sides. The resistance is located between the fulcrum and the effort. Since the effort arm is always longer than the resistance arm, a second-class lever can only be used to mUltiply

3. Third·Class Levers. In third-class levers, the fulcrum and resistance are at opposite ends of the lever. The effort is located somewhere between the fulcrum and the resistance. A shovel, your forearm . a fishing pole are ex­ amples of a third-class lever.

I":

1<

I

,iF

EA

RA

E

�I I

\! I

>- 1

I

� t

Third-class lever.

Since the resistance arm is always longer than the effort arm, a third-class lever always increases distance and speed at the exp�nse of force.

E

I���.--- EA ----l----�>�

I

�,,===I ="= = = = ======Til lifb = jJ! i

A .-L� =R=

i-F

:

I

GJ t

Second-class lever .

force but not speed. Some examples of second­ class levers are the wheelbarrow, nutcracker and paper cutter.

E

Examples of the second-class lever used to increase force.

Applications of the third-class lever used to gain speed and distance.

R

The Law of Moments. This law states that when an object is in equilibrium the sum of the counterclockwise moments is equal to the sum of the clockwise moments. The moment of a force is the product of the force and the perpendicular distance from its point of ap­ plication to the fulcrum. A moment produces rotation when the object is not in a state of equilibrium ( balance ) . When the sum of the counterclockwise moments equals the sum of the clockwise moments, the object is in a state of balance and no rotation occurs. The Law of Moments may be illustrated by the following problem of two boys on a seesaw : 33

Problem 1 :

�I<

1+- 4 ft.

�

78 1bs.

6 ft. � I

I

I

A

b

F

�� 1

u

52 1bs.

Law of Moments.

Counterclockwise moment

78 Ibs. X 4 ft. 3 1 2 ft.-lb.

= = =

Clockwise moment

52 Ibs. X 6 ft. 3 1 2 ft.-lb.

In this case, a 5 2-pound boy is capable of balancing a 78-pound boy because his effort ann is longer than that of the 78 -pound boy.

Problem 2:

SELF-DI SCOVERY ACTIVITY I nvestigating the Law of Moments.

Materials: Three meter sticks, 500 g. weight, a suit­ able fulcrum 2 to 3 cm. high.

�$�-

Counterclockwise moment

150 lbs. X 4 ft. 600 ft.-lb.

= = =

x =

Clockwise moment

1 00 lbs. X

1 00

6 ft.

x

ft.

x

Therefore, the boy must sit fulcrum to balance the man.

6

feet from the

Mechanical Advantage. The mechanical ad­ vantage (MA) of a machine represents the number of times that the machine multiplies the effort force ( the force applied to the machine) . The larger the MA, the less will be the force needed to overcome a resistance. The actual mechanical advantage of all ma­ chines is the ratio of the resistance to the effort. R Resistance = = . Actual MA Effort E Example:

A boy uses a lever on which he exerts 50 pounds of force to move a 2 50-pound rock. What is the actual mechanical advantage of this lever?

MA

=

!!:. E

=

250 lbs. 50 lbs.

=

5

�

�O-"'> 7 -"-'-t-:-::�-=== -: � ::=O--'/\ '-:: ""::O ---= 1=0 --=: "r=--='F I 1./ F2 1/

Procedure:

If a I SO-pound man were to sit 4 feet from the fulcrum of a seesaw, how far from the fulcrum must a I OO-pound boy sit to produce equilibrium?

34

The lever in this case has actually multi­ plied the boy's effort 5 times. If he were to attempt to lift the rock without the lever, he would have to exert at least 250 pounds of force.

A. 1. Place a suitable fulcr.lm under the 50-cm. mark (FI ) of two meter sticks, held together one on top of the other by rubber bands. A meter stick turned on edge makes a suitable fulcrum. Place the 500-g. weight over the extreme left-hand side of the meter stick as seen in the illustration. 2. Apply a downward force with your thumb on the I OO-cm. mark until the meter stick touches the table. 3. Measure the distance, in centimeters, through which the resistance and the effort move and record the data in the chart on the next page. M ake sure to take the thickness of the meter sticks into account. 4. Record the length in centimeters of the effort arm and the resistance arm. B. 1 . Move the fulcrum to the 20-cm. mark

(F i ) and repeat the preceding steps 1 -4 .

2. Use the Law of Moments to calculate the effort force when the fulcrum is at the 50-cm. and the 20-cm. mark. Conclusions: 1. This lever is a . . . . . . . . . . class lever.

2. When will the effort force be increased by the lever? . . . . . . . . . . . . . . . . . . . . . . . . .

DATA CHART

Poin t of Fulcru m

Di stance Effor t Mo ve s

Di stance Re si stance Mo ve s

Effor t

Re si stance

Ann

Ann

Effor t, Force

We can express the work done in moving an object up an incline by this formula: 3. When will the resistance move through

a greater distance in less time? . . . . . . . . . . .

Work Input

Effort

=

Work Output

=

(E)

X Effort Distance ( Length of Plane-L )

Resistance ( R ) X Resistance Distance ( Height of Plane-H)

4. What is the MA of the lever when the

fulcrum is at the 50-cm. mark? . . . . . . . . . . . ; the 20-cm. mark? . . . . . .

,

. . . . . .

.

. . . . . . . .

The Inclined Plane. The inclined plane is a simple machine used to reduce the effort needed to move an object. Stairs, winding mountain roads, planks leading from the street to a truck are all examples of inclined planes. Suppose we had to lift a heavy object onto a truck without using an inclined plane. Im­ agine the force we would have to exert ! Al­ though the effort is reduced by using an

t

6 ft.

In the above illustration the man moved the barrel 1 2 feet up the plane. If the plane were 6 feet high, how much effort would the man exert in raising the object this distance?

R X H 200 lbs. X 6 ft. 1 200 ft.-lb. E

= = = =

E X L E X 1 2 ft. 12 E 1 00 lbs.

The actual mechanical advantage of the inclined plane is obtained by dividing the resistance by the effort. Thus, the MA of this inclined plane is determined as follows :

MA

=R= E

200 lbs. 1 00 lbs.

=2

Useful applications of the inclined plans.

inclined plane, remember that this force must be exerted over a longer distance. Thus, the effort is less, but the work done is the same no machine saves work. If all losses are neglected, then theoretically, the work input should equal the work output. -

OTHER S I M PL E MACHINES

The Wedge. A wedge is a double inclined plane. When you slide a shovel under a pile of sand, the shovel is being used as a wedge. In using a wedge, a greater force must be applied to overcome a greater resistance. The 35

Materials: Scale, book, wire, 4-foot long board.

Procedure: A. 1. Record the weight of a school book. . . . . . . . . . . . . . . Five simple machines.

thicker the wedge, the greater must be the force. Long, thin, wedges have a greater me­ chanical advantage than short thick wedges. The ax, knife, chisel and screwdriver are some examples of wedges.

2. Attach a scale to the book; record the average force needed to raise it 2 feet. Lift at a uniform rate. Results : . . . . . . . . . . . . . . . . . . .

3. How do the weight of the book and the force applied compare?

The Screw. The screw is a circular inclined plane wrapped around a cylinder. Using it, we can overcome a large resistance with a small force. Some auto jacks, meat grinder, vise and propeller are examples of the screw. The Pulley. The pulley is a simple machine usually used to lift heavy objects. A fixed pulley is used to raise an o:,ject through a distance. It does not increase force but merely changes di­ rection. In using a fixed pulley you pull down­ ward to raise a weight. Moveable pulleys may be arranged to gain force at the expense of speed or distance and vice versa. To lift very heavy objects such as a piano you would use a combination of fixed and moveable pulleys called a block and tackle. The Wheel and Axle. The wheel and axle consist of two parts, a large wheel attached to a smaller circular axle. When we wish to gain force we must apply force to the outer edge of the large wheel. The resistance is applied to the axle. To gain speed we do just the opposite to what we did to gain force. What we gain in speed we lose in force. Some examples of the wheel and axle are the doorknob, steering wheel, eggbeater and bicycle pedal. S ELF-DISCOVERY ACTIVITY Work and the Inclined Plane. 36

2. Attach the scale to the book and determine the average effort force needed to pull the book from the bottom to the top of the incline. Make certain you apply a uniform force parallel to the incline. Record your results . . . . . . . . . . . . . . . . . .

3. What is the advantage of using the inclined plane? . . . . . . . . . . . . . . . . . . . . . .

.

4. Calculate the actual MA of the in­

cline when it is elevated 2 feet.

5. How much work is saved by using the inclined plane? . . . . . . . . . . . . . . . . . . . .

R EVIEW TESTS Completion Questions For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement :

1. A coiled snake, ready to spring at its prey is an example of . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

2. The efficiency of many machines is very poor and always less than 1 00 % because we must overcome the force of . . . . . .

.

. . .. . . .. . . . . . . . ... . .. . .. . .. . .. . .. .

.

.

.

. . .. . .. . . . . . .. . ... ..

3. A man exerts a force of 45 pounds to raise an object 6 feet. The work done is . . . . . . . . . . . . .

.

.

4. The simple machines include the lever, inclined plane, wedge, wheel and axle, and the . . . . . . . . . . 5. Two boys are sitting on

a

seesaw. One of them weighs 1 20 pounds and is located 4 feet from the

fulcrum. The other boy is sitting 5 feet from the fulcrum to balance the seesaw. How much does .

this boy weigh? . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

.

.

.

.. . .. . .. . .. . .. . .. . .. . .. . . . .. . .. . . .

6. An arrow let loose from a bow has . . . . . . . . . . . . energy. 7. What is the meaning of the term "kinetic energy?"

. . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . ..

8. The ratio of the resistance to the effort is a measure of the . . . . . . . . . . . . . . . . . . . . . . . . . of a machine.

9. (a) Winding mountain roads are actually applications of a simple machine called the

( b ) Why do mountain roads wind around a mountain instead of going straight up? . . . . . . . . . . .

(c) What must we sacrifice by using winding mountain roads? . . . . . . . . . . . . . . . . . . . . . . . . . . 10. A 1 20-pound boy ran up some stairs 20 feet high in 6 seconds. How much power did he develop?

11. What is the meaning of the term "work?"

12. What is the efficiency of a machine in which 800 ft.-lb. of work has been put in and 200 ft.-lb. put out? NAME

_______ ____

CLASS,

______

])ATE

__ __ __ __ __ __ __ __

37

13. When a force moves an object parallel to the applied force, . . . . . . . . is done. 14. A boy exerts a force of 80 pounds in trying to raise a box, but the box does not budge. How much .

.

15. Why can a second-class lever only be used to increase force? . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

work is done?

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

16. A baseball bat in use is an example of a . . . . . . . . -class lever with the . . . . . . . . . in the middle. Holding the bat closer to the bottom of the handle increases the . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

.

.

.

.

.

.

.

.

17. What does the Law of Moments state? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

18. What is the meaning of the term "moment?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

giving the advantage of more . .

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

. .

.

.

.

.

.

.

.

.. . .

.

.

.

.

.

.

.

-

19. An 80 p ound boy is sitting 6 feet from the fulcrum of a seesaw and a 1 00-pound boy is sitting 4 feet from the fulcrum on the same side as the 80-pound boy. How far from the fulcrum would a 200-pound man have to sit to balance the two boys? Show all work.

20. The mechanical advantage of a lever increases as the length of the . . . . . . . . . . . . . . . . increases. 21. A man exerts a force of 1 00 pounds to move a barrel 6 feet up an inclined plane which is 3 feet high. (a) What is the weight of the barrel? Show all work.

38

NAME

�CLASS

___ _ _ _ _ _ _ _ _ _ __

LJ DATE

_ _ _

_ _ _ _ _ _ _ _

(b) What was the quantity of work put in to accomplish this task? Show all work.

( c ) What is the actual MA of this inclined plane? . . . . .

.

22. An elevator lifts a weight of 528 pounds 1 000 feet in 2 minutes. How much horsepower is produced by the motor? Show all work.

.

23. In using a wedge, a . . . . . . . . . . .

.

..

.

. . must be used to overcome a greater

24. In using a screw, we can overcome a large . . . . . . . . . . . . . . . . . . with a small 25. When we want to gain force using the wheel and axle, we must . . . . . . . . . . . . . . . . . . . . . . . . .

.

Multiple-Choice Questions In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question. 1. A compressed spring represents (a) kinetic energy, (b) work, ( c) potential energy, (d) power. 2. In order to do work one must always ( a ) exert energy, ( b ) apply a force equal and opposite to the resistance, (c) oppose gravity, (d) move an object against a resistance. 3. A man exerts a 20-pound force on the handle of a suitcase and walks a distance of 10 feet while keeping the suitcase at a constant height of 3 feet. Which of the following represents the amount of work done on the suitcase? (a) 30 ft.-lb., (b) 200 ft.-lb., (c) 60 ft . lb. , (d ) 0 ft.-lb. -

4. A machine is used to ( a) multiply work, ( b ) do work with less effort, (c) create energy, (d) multiply effort and speed together. NAME

______

CLASS,

D �ATE

__ __ __

_ ______________

39

5. A hammer is used to remove a nail from a board. The hammer would represent a (a) first-class lever, ( b ) second-class lever, (c ) third-class lever, (d ) compound machine. 6. A unit of power might be represented by which of the following? ( a ) ft.-lb. , ( b ) % , ( c ) ft.­ lb./min. , (d) grams. 7. That point on which a lever is supported and is free to rotate is called the (a) effort, ( b ) resist­ ance, ( c ) moment, (d) fulcrum. 8. In melting wax, the main resistance met is (a) gravity, ( b ) molecular attraction, (c) friction, (d) inertia. 9. A man uses a lever having a mechanical advantage of 4 to move a SOO-pound mass. The effort force applied by the man is ( a ) increased by 4, ( b ) reduced by 4, (c) increased 1/4, (d) reduced by 1 /4. 10. A machine can never ( a ) save time, (b) increase force, (c) save work, (d) transform energy.

Matchi n g Questi ons In the space at the left of each item in Column A, place the letter of the term or expression in Column B that is most closely related to that item. . . .

.

.

.

. .

.

.

..

.

.

Column A

Column B

1. Application of a first-class lever

a . Human arm b . Kinetic energy c. Increase effort arm d. Wheelbarrow e . Moment f . Wedge g . Power h. Crowbar i . Has inertia j . Theoretical law of machines k. Law of Moments l. Energy m. Potential energy

.

. .

. .

.

.

2 . Simple machine

,

.

.

3. An object at rest or in a state of motion

. .....

.

.

4 . Work output

. . . . ... . .

.

.

.

.

. .

.

.

..

..

.

.

5. Third-class lever

6. Rate of doing work

.

.

7. Capacity to do work

.

.

8. Water behind a dam

. . . . . . . .

work input

.

. . . . . .

=

9. To multiply a force .

. . . . . . 10 Ability to produce rotation when the object is not in equilibrium

40

NAME

_______

CLASS

DATE

___

Chapter 5

P R ESS U R E I N FLU I DS D E NSITY

Which weighs the most - a pound of lead or a pound of feathers? Of course, a pound of one things weighs as much as a pound of any­ thing else. What makes the question tricky is that lead is much more dense than feathers, and you might be tempted to give an incorrect answer. But what if the question were restated as, "Which weighs the most - a cubic foot of lead or a cubic foot of feathers?

weight ( or mass ) of water is 62.4 pounds per cubic foot or 1 gram per cubic centimeter.

,

///� - - - - - - - - ---

,

1

1 cu. cm. MERCURY

cu. c,m .

WATER

1 L (1000

cu. ft. water

ml')

air

1 .29 g.

62.4 Ibs.

1 3.6 g.

1 g. ?

1

Example: An ice block 4 ft. long, 4 ft. wide and 3 ft. high weighs 2746 lb . What is the density of ice?

As scientists try to understand our physical world and search out the properties of matter, they must determine the density of various substances. Density is an important physical property of matter ; it tells us the weight ( mass) of a unit volume of matter. This is expressed mathematically by the following formula: D ( density)

"

W

(weight )

= ----­

V ( volume)

The units commonly used to express the density of solids and liquids are lb./cu. ft. (ft. 3 ) , read as "pounds per cubic foot" in the English system, and g/cu. cm. ( cmS ) , read as "grams per cubic centimeter" in the metric system. The density of gases is usually ex­ pressed in grams per liter (g/L ) . For example, the density of water is 62.4 lb. /cu. ft. or 1 g/cm3 • This means that the

D

2746

W

=

V

=

2746 lb. 48 cu. ft.

4 =

ft.

57. 2

X 4 ft.

lb.

X 3 ft.

Ib/ft3 (Density of ice)

Knowing density gives us a means of com­ paring the weights of equal volumes of differ­ ent substances. Pressure and density are closely related; the greater the density of a substance, the greater the pressure it can exert. Mercury barometers and manometers (in­ struments used to measure small pressures ) make use of the density of various liquids to measure pressure. The buoyancy or ability of objects to float is related to their density. Ob­ jects less dense than water, for example, will float in water; objects denser than water will sink. Engineers calculate the density of materials used in the construction of buildings, homes, 41

bridges, dams, boats, airplanes and subma­ rines. In space exploration, the density of ma­ terials is important since the volume and weight of space vehicles are limited by rocket fuels. Density also enables scientists to separate physically such materials as fluids having dif­ ferent densities.

PRESSURE

When you visit a doctor for a physical ex­ amination, the doctor will measure your blood pressure. When you breathe, air pressure forces air into your lungs. As man explores the ocean bottom and outer space, he must under­ stand pressure if he is to survive. Many machines depend upon liquid pres­ sure for their operation. Water pressure turns the huge turbines which run the generators that produce electricity. Hydraulic lifts are used to raise automobiles, and hydraulic presses can produce tremendous pressures to shape objects such as automobile fenders. Water stored in reservoirs and storage tanks produces pressures which enable water to flow from our faucets. Some machines depend upon normal air pressure of approximately 1 4.7 pounds per square inch for their operation. Vacuum clean­ ers, pumps which lift well water, siphons, and barometers are a few of the devices that de­ pend upon normal air pressure. Other ma­ chines use compressed air, that is, air under pressure greater than normal air pressure. Compressed air is used to operate submarines, tire pumps , air brakes and aqualungs. Caissons, devices in which men can work under water to construct the foundations of bridges and tunnels, for example, and pneu­ matic air tools such as air hammers and air drills use compressed air. To understand better the meaning of pres­ sure, we must understand the meaning of the term "force." Force is a push or pull that can produce, prevent or stop motion . Pressure is force exerted on a unit area of a given surface. 42

This may be expressed mathematically by the following formula : Pressure

=

--

Force Area

or P

=

F

-

A

Force is measured in weight units and area in square units. Pressure is usually expressed in the following units : English system :

lb./sq. in. or lb. /sq. ft. ( lb. /ft. 2 ) ( lb. /in2 )

Metric system :

g/sq.cm. ( g/cm2 )

or kg. /sq.m. ( kg/m2 )

If an area remains constant but the force exerted on the area is increased, the pressure will increase. Thus, pressure is directly propor­ tional to the force. If the force exerted on an area remains constant but the area is in­ creased, the pressure will decrease. Thus, pres­ sure is inversely proportional to the area.

Example:

A 1 20-pound girl wears shoes with pointed heels and each heel has an area of .05 in2 • The pressure on each heel due only to her weight when she stepped down would be 2400 Ib./in2 •

!.... = 1 20 lb: = 2 400 Ib./ in. 2 P= . .05 Ill . A The actual force is even higher than this since the extra muscular force was not taken into consideration. Pressures such as these can cause damage to many types of flooring and carpeting. If this same force of 1 20 pounds were evenly distributed over an area of 9 square inches, which is approximately the area of the heel of a man's shoe, the pressure would be re­ duced more than 1 8 4 times to a pressure of 1 3 . 3 lb./sq. in. p

= !.... = A

1 2 0 lb. 9 in. 2

=

1 3 . 3 Ib. /in. 2

The wide hoof of a camel, snowshoes, the dual tires on the landing wheels of airplanes and the casters on furniture are some of the devices which decrease pressure by distributing the force over a large area.

1. Liquid Pressure. The pressure exerted by a liquid depends on two factors : ( a ) the den­ sity of the liquid, and ( b ) the depth. The denser the liquid, the greater the pressure it will exert. Mercury has a density of 1 3 . 6 gjcm3 and, therefore, exerts a pressure 1 3 . 6 times greater than an equal volume of water. The fact that pressure exerted by liquids increases with depth is very important in the construction of dams ; they are thicker at the base than at the top. Submarines and diving bells must be built to withstand the increase in pressure as they descend deeper. Plants and animals that live in water have adaptations which enable them to equalize their internal pressures with the pressure of the surrounding water. The relationship of pressure to density and depth can be expressed mathematically by the following formula: Pressure = Height X Density or P ( Depth )

.

H X

D

Example :

What is the pressure exerted on the bottom of an aquarium filled with water to a depth of 2 feet? P=H X D = 2 ft. X 62.4 lb. jft3 = 1 24 . 8 lb. jft2 2. Total Force. Up to this point we have been concerned with pressure; that is, the amount of force exerted on a unit of area. But suppose we wanted to find the amount of force being exerted by water against the bottom of an aquarium. The force exerted on the total horizontal surface is the total force ( TF) . This force can be calculated by multiplying the pressure by the total area of the surface.

Density of water = 62.4 lb. jft3 Area of bottom of aquarium L X W = 3 X 2 = 6 ft. 2

TF = = =

=

H X D X A 2 ft. X 62.4 lbjft3 X 6 fe 748 . 8 lb. ( 749 lb. )

3. Total Force on a Vertical Surface. We have learned that pressure exerted by a liquid increases with depth. To calculate the pres­ sure against a wall of a tank or against a dam we must take into account that the pressure is least at the top of the liquid and greatest at the bottom. Therefore, to obtain the pressure against a vertical surface, we must actually find the average pressure at the midpoint of the surface or average depth. To find average pressure, multiply the height (in feet) by the density (in this case, 62.4 lb. ) , and divide by 2. This can be shown by the formula: H X D AF = 2 2 X 62.4 AF = 2 AF = 62.4 lb/ff2

To find the total force, multiply the average pressure by the total area of all the sides of the aquarium. Use the formula below : TF = AF X A ( area) What is your answer? . . . . . . . . . . . . . . . .

.

4. Effect of Shape, Size and Volume on Pressure. The shape, size and volume of a con­ tainer have no effect on the pressure of the liquid inside it so long as the depth and density remain constant.

Total Force = Pressure X Area Total Force = H X D X A ( pressure) Example:

The total force exerted on the bottom of an aquarium 2 feet high, 3 feet long and 2 feet wide, filled with water, is calculated as follows :

Uquid pressure is unaffected by the shape, size or volume of the container. 43

So long as the pressure remains the same, the liquids in these containers will rise to the same level. It is this equality of pressure that explains the expression "water seeks its own level." 5. Liquids Exert Pressure Equally in All Directions at the Same Depth. If you ever tried to push a board below the surface of deep wa­ ter, you felt the resistance caused by the up­ ward push of the water. Water flowing from a hole in the bottom or side of a container indi­ cates that the water also exerts a pressure downward and sidewise. Thus, we can say : ( a ) Liquids exert a pressure in all direc­ tions ( b ) At the same depth, the pressure ex­ erted by a liquid is the same in all directions.

the lower hole, and one about 1 inch from the top, slightly to the right of the middle hole.

2. Plug each of the holes with a round toothpick, after removing the end which burns. 3. Fill the can with water and place it at the edge of a sink as seen in the illustration. 4. Q u i c k l y remove each toothpick and observe the results.

Observations: What did you observe about the flow of water from each of the three openings? . . . . .

Liquid pressures. The arrows illustrate that a liquid exerts pressure in all directions.

The

sures

equal

are

manometer in

all

ind icates

directions

at

that the

l i quid same

pres­ depth.

Conclusions: Explain your observations.

SELF- DI SCOVERY ACTIVITY Exploring the Relationship Between Water Pressure and Depth.

Materials: One empty metal container of about 1 gal­ lon capacity, hammer, small nail, round tooth­ picks.

Procedure: 1. Puncture three small holes in one side of the container. One hole should be at the bot­ tom, one in the middle, slightly to the right of 44

6. Pascal's Law and Hydraulics. Man has invented many devices which operate by pres­ sure. Devices which transmit force by means of liquids are known as hydraulic machines.

250 Ibs.

The operation of hydraulic machines such as hydraulic lifts, hydraulic presses and hydraulic brakes is based upon two primary principles :

1 0 1bs.

( a ) Fluids ( which include liquids and gases ) are very resistant to compres­ sion and can be used to transmit and multiply force. ( b ) Pascal's Law, which states that pres­ sure applied to a confined liquid is transmitted undiminished equally to all parts of the liquid, and acts in all di­ rections. A hydraulic lift or hydraulic press consists of two tightly fitting pistons, one small and one large, each enclosed in a cylinder filled with a fluid, often oil. These cylinders are connected at their bases by a pipe. The pistons can move up and down in their cylinders. If a force of 10 pounds were exerted on the small piston, whose area is 2 in�, it would produce a pressure of

5

Ib/in2 (P

= F)

. This pressure is A transmitted undiminished through the oil to the large cylinder where it acts on the large piston. Let us now see what effect this pressure has on the large piston. If the area of the large piston is 50 in2 , and a force of 5 pounds is ex­ erted on every square inch, it would produce a total force of 250 pounds. -

F=

P X A 5 Ib./in2 X 50 in2 = 250 lbs.

=

This relationship may be expressed mathe­ matically by the following ratio : Force on large piston

Area of l arge piston

Force on small piston F A

Area of small piston

a

f

F 50 in2 2 in2 1 0 1bs. F 250 lbs. =

As you have learned in our discussion of levers, any gain in force must be paid for by

The hydraulic lift.

glVlng up distance and/or speed. The small piston must be moved through a greater dis­ tance to bring only a comparatively small up­ ward motion of the large piston. The mechan­ ical advantage of a hydraulic lift is obtained by dividing the area of the larger piston by the area of the smaller piston.

MA

=

� = 50 a

2

in.2 in.2

=

25

This lift would multiply the input force 25 times. We would, for example, only have to apply a force of 800 pounds to lift a 20,000pound weight. However, the small piston would have to move a distance 25 times greater than the distance moved by the large piston. The MA of a machine is also the ratio of the effort distance ( Ed ) to the resistance distance (Rd) . If the MA is 25, then the distance moved by the small piston ( Ed ) is 25 times greater than the distance moved by the larger piston ( Ra) . Example: If the MA is

25 and the resistance moves 10 inches, then the effort force must be applied through a distance of 250 inches. Ed MA =

Rd

25 = � 1 0 in. Ed = 250 inches. 45

S ELF-DI SCOVERY ACTIVITY I nvestigating Hydraulic Pressure.

Materials:

3. Have a student stand on the board. Ex­ tend the tube and funnel vertically to its full length. 4. Pour water into the funnel until the bag and most of the tubing are filled. 5. Empty the hot water bottle and calculate the area in square inches of that surface of the

A hot water bottle, one-hole stopper large enough to seal the opening of the hot water bottle, a piece of glass tubing, 6 feet of plastic or rubber tubing, a funnel, and a flat board.

bottle on which the student stood. Area : . . . .

Procedure:

Observations:

1. Insert a piece of glass tubing into the one-hole stopper and attach the six-foot tubing to it. Insert the stopper very securely into the hot water bottle and attach a funnel to the other end of the tubing. 2. Lay the bottle on the floor and place a fiat board on it.

Describe your observations.

Conclusions: 1. The water pouring into the funnel acted as a . . . . . . . . . . . . . . . . . , whereas the water pressing in on all interior surfaces of the hot water bottle represented . . . . . . . . . . . . . . . . . 2. If the force exerted by the water that en­ tered the bag was 3 pounds, what would be the total pressure exerted on the upper surface of the bag which was responsible for causing the

effect on the student? Total pressure: . . . . . . .

3. What law is involved in this portion of this activity and what is the principle of this law? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

46

.

R EVIEW T ESTS Completion Q uestions For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement.

1. What is the difference between the weight and density of a mass? . . . . . . . . . . . . . . . . . . . . . .

.

2. Why is a knowledge of density important?

(a)

(b)

3 . A 1 000-g. mass i s 5 cm. long, 2 cm. high and 4 cm. wide. Its density i s . . . . . . . . . . . . . . . . . . 4.

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forces air into our lungs.

5. What is the difference between force and pressure?

6. If a card is 6 inches long and 4 inches wide, how much force of air is pressing on one surface?

7. Why is the bottom of a dam thicker than its top? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(a) What is

8. A dam is 30 feet wide. The water behind the dam reaches a height of 20 feet. Ithe average pressure exerted on the dam? .

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( b ) What is the total force exerted

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10. Compressed air is air under a pressure greater than . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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CLASS

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9. What are caissons? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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against the dam?

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47

11. Why do some girls' high-heeled shoes cause so much damage to carpets and certain types of floor

covering?

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12. Some steam irons have a transparent tube which indicates the quantity of water in the iron. How

does this show the amount of water in the iron? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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13. Water is very resistant to . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . and can thus be used to transmit and mUltiply force . 14. What is Pascal's Law? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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15. A hydraulic press has a piston with an area of 6 sq. in. and a piston with an area of 96 sq. in. ( a ) If a force of 50 lbs. is exerted on the small piston, what will be the force exerted on the large piston? . . . . . . . . . . . .

( b ) The pressure exerted on the small piston is ( c ) The pressure exerted on the large piston is ( d ) What do we sacrifice to gain an increase in force when using this machine? . . . . . . . . . . .

.

( e ) What is the MA of this machine? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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16. How do furniture casters protect carpeting and flooring? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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17. Why is the density of materials of prime importance to space scientists? . . . . . . . . . . . . . . . . . .

.

48

NAME

����_

��_

CLASS

DATE

___

_ _ _ _ __ _ _ _

18. What are four machines that depend upon normal air pressure ( 14.7 pounds per square inch)

for their operation? (a) (b) (c) (d) .

19. The pressure exerted by a liquid depends upon the . . . . . . . . . . of the liquid and the . . . . . . . . .

of the liquid. 20. What is the total force exerted on the bottom of an aquarium that is 2 feet high, 2 feet wide and .

5 feet long?

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Mu ltiple-Choice Questions

In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question. 1. Which of the following units would be used to express density? ( a ) gms., ( b ) Ib/ft2, ( c ) ft/lb, (d) g/cm3. 2. Which of the following will not affect water pressure? ( a ) a change in depth, ( b ) a change in volume but not height, ( c ) a change in area, (d) a change in density.

3. An aquarium 2 ft. long, 3 ft. high and 1 ft. wide is filled to the top with water. Which of the following represents the pressure exerted on the bottom of the aquarium? ( a ) 56 1 . 6 Ib./ft2, ( b ) 1 8 7 2 1b /ft2 ( c ) 1 g/cm3 , (d) 62.4 Ib./ft3 . .

4.

.

,

An object is submerged 2 feet below the water. The pressure exerted on this object is ( a ) stronger from above, ( b ) stronger from below, ( c ) equal in all directions, (d) insufficient information to draw a conclusion.

5. The operation of a hydraulic lift is dependent upon ( a ) buoyancy, ( b ) Pascal's Law, (c) New­ ton's law of gravity, (d) Einstein's law of relativity. 6. Which of the following weighs the most?

pound of feathers, (d) none of these.

( a ) a pound of lead,

( b ) a pound of water, ( c ) a

7. A metal block 2 ft. by 4 ft. by 6 in. weighs 520 pounds. Its density is ( b ) 1 3 0 Ib./ft3, ( c ) 2 4 9 60 Ib /ft3 ( d ) 2080 Ib./ft3 • ,

.

,

(a)

1 0 . 8 lb ./ft3,

8. Water has a density of ( a ) 1 g/cu. cm, ( b ) 62.4 g/cu. ft. , ( c ) 1 .29 giL, (d) 1 3 .6 g/cu. cm. 9. An instrument used to measure small pressures is called a ( c ) hydrometer, (d) manometer. 10. Which of the following is used to raise an automobile? I( c) hydraulic lift, ( d ) air brake.

NAME

_______

CLASS

___

( a ) thermometer,

( a) hydraulic press,

DATE

( b ) slide rule, ( b ) turbine,

_ _ _ _ _ _ _ _

49

Matching Q uestions

In the space at the left of each item in Column A, place the letter of the term or expression in Column B that is most closely related to that item. Column A

Column B

a. Density of water

1. Measures air pressure

b. Will float c. Hydraulic machines d. Mercury e. Barometer f. Different densities g. Water pressure h. Will sink i. Operates on compressed air j. Snowshoes k. Pressure I. Density m. Thermometer

2. 1 3 . 6 times denser than water

3. Separation of water and oil 4. I g/cu. cm

5. Objects whose density is less than water 6. Often turns huge turbines which operate

generators 7. Aqualungs 8. Force/unit area 9. Reduces pressure by distributing weight over a large area

. . . . . . . . 10. Transfer force by means of liquids

50

NAME

_______

CLASS,

DATE

___

_ _ _ _ _ _ _ _

Chapter 6

B U OYA NCY A N D S P EC I F I C G R AV I TY B UOYANCY

If you have ever been swimming in Great Salt Lake in Utah or in the Salton Sea of Cali­ fornia, you found that you could float easily in the heavy saltwater. Yet, a rock will sink, even in sllch a dense liquid. Why do some objects float and others sink? Fluids (both liquids and gases ) , as you have� learned, exert pressures in all directions. The upward force exerted by a liquid opposes gravity; therefore, objects either completely or partly submerged in a liquid appear to weigh less than they do in air. This upward force is caIle:d buoyancy. Objects which float do so because of this buoyant force. Buoyancy and the resulting ap­ parent loss of weight explain why a scuba diver can wear heavy air tanks, the weight of which becomes insignificant in water. The huge blue whale, which may be over 1 00 feet long and weigh over 300,000 pounds, is the largest animal on this planet. Its tremendous weight is supported by the buoyant force of water. Land animals never reach this size. Their weight would be so great that movement and survival would be impossible.

1. Archimedes' Principle. When you take a bath or place an ice cube in a glass of water you and the ice cube displace a certain amount . of fluid and, therefore, the water level rises. Archimedes, a famous Greek mathematician, related buoyancy and the weight of the fluid displaced to explain why objects float or sink. Archimedes' Principle states that an object im-

mersed in a fluid seems to lose weight and the apparent loss in weight is equal to the weight of fluid displaced. This principle can also be restated as : A n object immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced. ( Buoyancy = weight of dis­ placed fluid. )

2. Why Does an Object Float? You throw a piece of solid metal into the water and it sinks. A metal ocean liner weighing many thousand of tons floats. Why? This is explained by the Law of Flotation which states that : Objects will float when the weight of the object is equal to the weight of the displaced fluid (buoyant force). Thus, an object will sink only to a depth at which it will displace enough fluid to equal its own weight. The weight of the displaced fluid is depend­ ent upon the ( a ) weight of the object, and ( b ) the volume of the object. Since the weight of a ship, other than a submarine, remains ap­ proximately the same, the huge mass of metal is made to float by increasing its volume so it will displace more fluid. This is done by shap­ ing the metal into a huge, hollow hull. A boat weighing 3 tons will sink until it just displaces 3 tons of water. The volume of the water moved out of its original position by the boat is referred to as the displacement of the boat. Knowing the density of water and the weight of the vessel, we can use a variation of the density formula to figure the displacement of the boat. v = W

D

=

6000 lb. 62.4 lb. jft. 3

=

96 ft. a ( displacement)

Clouds, dust, and balloons float in our at­ mosphere for the same reasons as objects placed in liquids ; that is, they displace their own weight.

3. Why Does an Object Sink? An object will sink when its weight is greater than the 51

weight of the fluid it displaces. A solid block of metal does not have sufficient volume to dis­ place enough fluid to equal its own weight. A submarine can sink or rise by changing its weight. This is done by flooding or empty­ ing ( venting ) its ballast tanks located between the outer and inner walls of the submar ine. When a submarine submerges, water floods the ballast tanks, making the submarine heavier so it will sink. When a submarine surfaces , the ballast tanks are vented, making the submarine lighter. The ability of an object to float is also re­ lated to the density of the liquid in which it is located. Denser fluids exert a greater buoy­ ant force ; a block of iron will sink in water but will float in mercury. An object which will float in water will sink deeper in gasoline which has a density of only . 7 g/cm3 as com­ pared to 1 g/cm3 for water. Of course, it will only sink until it displaces a volume of gasoline equal to its own weight.

collect all the water that overflows in the 500 ml. beaker. 5. Weigh the beaker containing the dis­ placed water and record the results. 6. Compute the weight of the displaced water. 7. Measure the volume of the displaced water in milliliters (cc).

SELF-DISCOVERY ACTIVITY

pare? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

DATA CHART

Weight of wood Weight of empty beaker Weight of beaker + water Weight of displaced water Volume of displaced water

Conclusions: 1. How did the weight of the wooden block and the weight of the displaced water com-

Exploring Archimedes' P rinciple

Materials: .

2. When did the block stop submerging?

An overflow can, a balance, a block of wood approximately 1 Y2 " X 1 Y2 ", a gradu­ ated cylinder, a 500 ml. beaker.

Procedure: 1. Carefully obtain the weight of the block of wood in grams, and record the weight in the data chart. All future data collected is to be recorded in this chart. 2. Carefully weigh a dry, empty 500 ml. beaker and record your results. 3. Fill the overflow can with wa­ block of wood ter ; allow excess fluid to escape. 4. P l a c e t h e block of wood into the overflow 500 ML BEAKER can and carefully 52

3. What is the relationship between the volume of the wood block and the volume of the displaced water? . . . . . . . . . . . . . . . . . . . .

SPECIFIC G RAVITY

In order to compare the density of various substances we must use standards of com­ parison. Specific gravity (specific weight) is the ratio of the density of a substance compared to a standard reference. The standard of refer­ ence for most liquids and solids is water, with

a density of 1 g/cm3 or 62.4 lb./ft3• The den­ sity of air ( 1 .2 9 g/L) is the usual standard of reference for most gases. The specific gravity of solids and liquids is calculated by comparing the weight of a defin­ ite volume of the given substance to the weight of an equal volume of water. This is expressed mathematically by the following formula : Speel· fic Gravlty ·

=

1. Determining Specific Gravity of Solids Denser Than Water. To determine the specific gravity of solids denser than water, first weigh the object in air and then in water. The differ­ ence between these two weights represents the weight of an equal volume of water or the buoyant force of water.

Weight of object in air

= ---.;::;;,.... ---=:...----

Weight in air - weight in water

This formula can also be expressed as : S peel·fi c Gravtty ·

=

50 g.

l OO g. I --- SCALE

Weight of a subs tance ___�.:..____________ Weight of an equal volume of water

Specific gravity has no units because it is a ratio and is numerically equal in both the English and the metric systems.

Speel·fi c · Gravlty ·

___

--

Weight of object in air __....___ ...::. Loss of weight in water _--l:"--

Determining specific gravity of a solid denser than water.

Since objects less dense than water will either float on the surface or be only partly sub­ merged, we must attach a sinker to the object so it can be completely submerged. This is nec­ essary so we can determine the weight of an equal volume of water. After the sinker is attached, we submerge only the sinker in the water and record its weight. We then submerge both the sinker and the object and record their combined weight. The difference between these two weights rep­ resents the weight of a volume of water equal to the volume of the unknown object.

_

Example:

A stone weighing 1 00 grams when weighed in air weighed 50 grams when submerged in wate:r. What is the specific gravity of the stone? Specific Gravity

=

1 80 g.-

I ---- SCALE

Weight in air Weight in air - weight in water

1 00 g = 2 1 00 g - 50 g 2. Determining Specific Gravity of Solids Less Dense Than Water. To determine the specific gravity of solids less dense than water, we first obtain the weight of the object in air.

r-:;:;:;;;:;;;t;;;;;;;;r

r-iiiiiiii--

WATER OBJECl LESS DENSE THAN WATER SINKER

Determining specific gravity of a solid less dense than water. 53

Example:

An object less dense than water weighed 80 grams in air and the weight obtained after sub­ merging only the sinker was 1 8 0 grams. The weight of the sinker plus the object when both were submerged in water was 20 grams. What was the specific gravity of the object? Specific Gravity

2. Attach a string to the stone and sub­ merge it in water and record its weight. ( Do not allow the stone to touch the bottom

or sides of the beaker. ) . . . . . . . . . . .

.

. .

.

.

3. Compute the specific gravity of the stone.

=

Weight of object in air Weight of submerged sinker - weight of submerged sinker + object. 80 g. 1 80 g.

-

20 g.

=

80 g. 1 60 g.

=

.

5

Conclusions: .

1. What is specific gravity?

The specific gravity of an object whose den­ sity is less than that of water will always be less than 1 .

SELF-DISCOVERY ACTIVITY Determining the Specific Gravity of a Solid Denser Than Water

2. The loss of weight of the stone when submerged equals the buoyant force of the

water or the . . . . . . . . . . . . . . . . . . . . . . . . .

Materials: Scale, beaker, stone, string.

WEIIN AIGHTR

WEIIN WATEGHT R �lllf--WATER STONE

Procedure: 1. Weigh a stone in grams and record its weight. 54

3. Specific Gravity of Liquids. The specific gravity of liquids is determined by using an in­ strument called a hydrometer. The scale of the hydrometer indicates spe­ 1 .075 cific gravity. If it were 1 .100 placed in water, it would 1 .125 1 . 1 50 submerge until it reaches 1 . 1 75 the 1 .000 level on the 1 .200 1 .225 scale. If placed in a less 1 .250 dense liquid such as kero­ 1 .275 1 .300 sene, the hydrometer will sink below the 1 .000 level, since the liquid produces less buoyant force. If placed in a denser liqBattery uid, such as battery fluid hydrometer. which contains sulfuric acid and water, it will

WEIHYD��GHT TETOR STRAIGHT

not sink as far as the 1 .000 level since its buoyant force is greater than that of water. When a battery is fully charged the hy­ drometer reading will be about 1 . 300; if poorly charged the specific gravity will be much less. The hydrometer is also used to check the freez­ ing point of radiator water containing anti­ freeze to determine its effectiveness. 4 Uses of Specific Gravity. A knowledge ..

of specific gravity helps the scientist to identify minerals and rocks. The degree of purity of some liquids and the concentration of acids may be determined by specific gravity. We have: seen that the degree of charge of a stor­ age battery and the degree to which antifreeze prevents radiator water from freezing is also obtained by determining the specific gravity of the fluids. The specific gravity of the body fluid urine is also used to help indicate the presence of certain diseases. 5. Bernoulli's Principle. Most people stare in utter amazement as a huge airplane wings its way across the heavens. They often say: "It's a miracle that such a huge machine can fly! " The ability of aircraft to fly is not a miracle; it is based on sound scientific principles. According to A rchimedes' Principle, the airplane should fall since it is heavier than the air it displaces. What then keeps it up? Early in the 1 8th century, a Swiss scientist named Daniel Bernoulli carried out experi­ ments with fluids flowing over various surfaces. He learned that as the speed of a fluid ( liquid or gas ) over a surface increased, the pressure

on that surface decreased. This discovery later became known as "Bernoulli's Principle." An understanding of this principle made it possible to build airplane wings that could produce enough lift to overcome the force of gravity. The wings are designed with a greater curva­ ture on the upper surface so that the air mov­ ing above their surface moves faster than below their surface. Then, according to Bernoulli's Principle, the pressure above the wings is less than that below the wings. This decrease in pressure actually produces a partial vacuum above the wings. It is the larger pressure below the wings that provides the essential lift. The pressure is due to air pressure operating at a pressure of 1 4. 7 Ib. /in2 • The larger the wing, the larger the lifting force. Factors other than wing area also affect the lifting force. These include : ( a ) Air speed. Lift varies as the square of the air speed, thus the lift is increased by four times by doubling the speed. ( b ) Shape of the wing. A curved stream­ lined wing produces the difference in velocity of the air moving above and below the wings with as little turbulence (disturbance) as possi­ ble. ( c ) Angle of tilt of the wing. An airplane will stall if the tilt of the wing is too great with respect to the relative wind. The relative wind is the wind flowing over the wings and is al­ ways opposite in direction to the direction in which the plane is traveling. 6. Other Forces Acting on an Airplane. An airplane must not only stay up but must move

Forces acting on an airplane - BernOUlli's Principle. 55

forward. The propellers or jets provide the thrust or force which propels the plane for­ ward. This thrust is constantly opposed by an opposite force which tends to slow the forward motion. This opposing force is called drag. 7. Devices That Operate on Bernoulli's Principle. The ability of an airplane to stay aloft is, in part, dependent upon this principle. The wind passing over a chimney produces a low pressure area above the chimney, causing an updraft since the air will always move from a region of high pressure to a region of low pressure. Liquids or gases moving through a tube whose diameter changes also follow Bernoulli's Principle. As the diameter of the tube de­ creases, the velocity of the fluid increases. As the velocity increases, the pressure decreases. This is illustrated below in a pipe called the Venturi tube and some examples of apparatus that operate upon Bernoulli's Principle. Many kinds of atomizers, the Venturi in carburetors which speeds the vaporizing of the gasoline, the ability of a kite to fly, and a base­ ball to curve are also dependent upon Ber­ noulli's Principle.

HIGH

HIGH SLOW

� --��--�----

The Venturi tube.

Materials: A spool, a straight pin, a piece of 3 x 5 card cut to a two-inch square, a piece of paper 3 inches by 1 1 inches.

Procedure: 1. Place a pin through the center of the t w o-i n c h s q u a re and insert the pin into one of the openings at either end of the spool. 2. Lightly hold the card in place with a finger, and keeping your cheeks puffed in the way a tuba player does, blow air into the open top hole of the spool.

3. While holding the spool with your other hand, remove your finger from under the card. Observe. 4. Grasp the 3" x I I " paper at one end. Now blow vigorously over the paper. Observe.

Observations: 1. What happened the card in terms of Ber­ noulli's Principle?

WIND RED� UCED PRESSURE �

I

� c:-eg

p CEJca

I

,

-::::;;:- ====;��

o

Chimney.

A tomizer.

Applications of Bernoulli's PrinCiple.

2. What happened to the paper in terms of

Bernoulli's Principle? . . . . . . . . . . . . . . . . . . . SELF-DI SCOVERY ACTIVITY Investigating Bernoulli's Principle 56

R EVI EW T ESTS Completion Questions

For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement. 1. The specific gravity of an object is equal to its weight in air divided by the weight of

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . of water. 2. An object weighed 60 g in air and 40 g when submerged in water. The specific gravity of the

object was

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3. If a substance floats in water, its specific gravity is less than . . . . . . . . . . . . . . . . . . . . . . . . . . .

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4. List three ways in which a knowledge of specific gravity is useful.

(a) (b) (c) 5. The upward force exerted b y a liquid opposes the force of

6. The upward force which keeps an object floating is called 7. An abnormal specific gravity of urine may indicate the presence 6f a ( an ) . . . . . . . . . . . . . . . . . 8. The apparent loss in weight of

an

.

object immersed in a fluid is equal to the . . . . . . . . . . . . . .

9. If a boat displaces 200 cubic feet of water, its weight is . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10. Why will a block of iron sink in water? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11. As the density of a fluid increases, its buoyant force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

12. How does the force develop that lifts an airplane off the ground and keeps it aloft? . . . . . . . . . . .

NAME

_______

CLASS

L' DATE

_ _ _

_ _ _ _ _ _ _ _

57

13. Bernoulli's Principle states that . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

14. Theoretically, if the speed of an airplane is tripled, its lift will be increased . . . . . . . . times. 15. The engines of jet planes provide the . . . . . . . . which moves the plane forward.

16. The relationship between buoyancy and the weight of displaced fluid was first explained by

17. The weight of displaced fluid is equal to the . . . . . . . . . . . . force acting upon an object. 18. The first step in determining the specific gravity of an object is to obtain its weight in 19. The specific gravity of an object that floats in water will always be . . . . . . . . than 1 . 20. The force that opposes forward motion of an airplane is called 21.

. . . . . . . . is the force on an airplane wing that counteracts gravity.

22. Ordinary air pressure is equal to . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . at sea level. 23. A disturbance in the air moving above and below the wings of an airplane is known as . . . . .

24. The Venturi tube operates on principles first explained by . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25. What does the term "relative wind" mean? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

26. In order to check the freezing point of water in an automobile radiator containing antifreeze, we use an instrument called a ( an ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

27. A wind passing over a chimney produces a low pressure area over the chimney causing a ( an)

28. A knowledge of . . . . . . . . . . . . . . . . . . . . . . . . . . helps scientists to identify minerals and rocks. 29. Why do specific gravity figures have no units? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

30. Why is it possible for a balloon to float in the atmosphere? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

58

�A1v[E

_______

CLASS

� DATE

______

__ __ __ __ __ __ __ __

Mu ltiple-Choice Questions

In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question. 1. If the velocity of a fluid increases steadily, the pressure will ( c ) fluctuate, ( d ) remain the same.

2. An instrument used to measure specific gravity is drometer, ( d ) hydrophyte.

(a) increase,

( a ) hygrometer,

( b ) decrease,

( b ) manometer,

(c) hy­

3. An object will submerge until it displaces its own (a) weight, ( b ) specific gravity, (c) volume, ( d) density. 4. A submarine submerges by ( a ) venting the ballast tanks, ( b ) increasing its buoyancy, (c) decreasing its weight, ( d ) flooding the ballast tanks with sea water.

5. In order to make a huge metal ship float , the metal is shaped into a hollow hull to (a) increase its density, ( b ) increase its volume, ( c) increase its weight, ( d ) none of these.

6. The principle that an object immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced was developed by ( a ) Pascal, ( b ) Bernoulli, ( c ) Archimedes, ( d ) Newton.

7. An iron ball will sink in water but will float in mercury because mercury (a) has lower specific gravity, ( b ) decreases the buoyant force, (c) is denser, ( d ) has a greater surface tension.

S. An object which floats in water weighed 60 grams in air. After submerging it in water with a sinker attached, it weighed 10 grams. The weight with the sinker alone submerged was 1 60 grams. The specific gravity of the object was ( a) 2.6, ( b ) . 3 , ( c ) .4, (d) .75.

9. Which of the following is not dependent upon Bernoulli's Principle? (a) Venturi tube, (b) atom­ izer, ( c ) air hammer, ( d ) chimney.

10. A fluid passing through a tube suddenly enters a tube of a smaller diameter. Which of the follow­ ing effects will result? ( a ) The velocity decreases. ( b ) The pressure increases. ( c ) The velocity remains constant. ( d ) The pressure decreases. 11. Fluids exert pressure ( a ) to the sides, ( b ) upward, ( c ) downward, ( d ) in all directions.

12. If an objects floats in water, when it is placed in gasoline, which has a lower density, it will ( a ) sink deeper and still float, ( b ) , sink to the bottom, ( c ) sink deeper and possibly will float, ( d ) not sink deeper and will float. 13. The density of air is (a) 62 .4 Ib./ft3, ( b ) 62.4 giL, ( c ) 1 .29 lb./fta, ( d ) 1 .29 giL.

14. Air traveling across the top of an airplane wing moves (a) faster than the air below the wing, ( b ) slower than the air below the wing, ( c ) at the same speed as the air below the wing, ( d ) at times it moves slower and at times faster than the air below the wing. 15. Which of the following does not directly affect the lifting force of an airplane? ( b ) wing shape, (c) angle of wing tilt, ( d ) drag.

NAM E

_________

( a ) air speed,

59

Matching Questions

In the space to the left of each item in Colu mn A, place the letter of the term or expression in Column B that is most closely related to that item. Column B

Column A

Water b. Archimedes' Principle c. Drag d. Dinosaur e. Bernoulli's Principle f. Fully charged battery g . Poorly charged battery h. Specific gravity i. Mercury j. Blue whale k. Kerosene ! . Reduces turbulence and produces a difference in velocity above and below an airplane wing m. Displacement n. Venturi tube

1. Determining the freezing point of radiator water containing antifreeze

Q.

2. Opposes thrust 3. Specific gravity

=

1 . 300

4. Volume of water pushed aside by a sub­ merged object 5. Standard for determining the gravity of liquids

specific

6. Curved streamlined design 7. Throwing a curve ball 8. Part of carburetor to help vaporize gasoline 9. Largest animal ever known to exist 10. Hydrometer will sink farther in this liquid

than in water

60

NAME

,CLASS,

_______

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DATE

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Chapter 7

FORCES A N D M OT I O N EAS T �

\ B-�

MOTION

Motion is the continuing change in the posi­ tion of an object relative to a point of refer­ ence. If you were sitting in a flying airplane, would you be moving? The answer to this question depends upon your point of reference. As you sit in your seat you would be motion­ less with respect to the airplane; however, you would be in motion with respect to the earth. To detect motion, a point of reference is needed. If you were high in a plane above the earth and you looked out the window and saw only empty sky you would not be able to detect mo­ tion since there is no point of reference. When some fluffy white clouds finally come into view you could see motion, for you can compare your motion to that of the clouds. Even this motion may be deceiving for it may be difficult for you to decide whether the movement is that of the airplane or the clouds or both. 1. Speed and Velocity. The rate at which an object moves is called speed. The speed of an object can also be thought of as how far an object travels in every unit of time that it con­ tinues to move at a particular speed. Miles per hour ( mi.jhr., mph ) and feet per second (ft. /sec.) are two units used to express speed. Speed, as you have learned, is a scalar quantity since it has magnitude ( size or quantity ) only. In describing the motion of a body, we usu­ ally give a more complete description by speaking of its velocity instead of its speed. Velocity is a vector quantity since it describes two things about a moving body: ( a ) its direc­ tion, and ( b ) the magnitude of the distance moved per unit time. If an automobile is traveling at the rate of 60 miles per hour, we would refer to this as its speed. If it were stated that the automobile was traveling east at 60 miles per hour, we

60 MPH

60 M'P H

Magnitude only = speed.

Magnitude + direction = velocity.

would be speaking of its velocity. Velocity is the rate at which an object moves in a given direction. 2. Unifonn and Accelerated Motion. All motion can be classified as one of two types: ( a ) uniform motion, and ( b ) accelerated mo­ tion. If an object travels the same distance and in the same direction in the same successive time intervals, its velocity will remain constant. Such motion is called unifonn motion. The dis­ tance traveled may be expressed mathemat­ ically by the following formula:

Distance = Velocity X Time d or s = v X t

For example, if a supersonic airliner traveled due east with a uniform motion of 1 000 mph for three hours, it would travel a distance of 3 000 miles.

-

Uniform motion.

� -�.

� --

d=v X t d = 1 000 mi./hr. X 3 hrs. d = 3 000 miles Suppose you were riding in the family car and your father stepped down harder on the accelerator (gas pedal ) . Since the speed of the car would increase, we say that the car is ac­ celerating or undergoing positive acceleration. 61

Acceleration of an object in motion occurs when there is a change (gain or loss ) in veloc­ ity. If the automobile changed its velocity at a constant rate, that is, by the same amount dur­ ing each unit of time, the car would be said to be undergoing uniform acceleration. In com­ puting acceleration, time enters into the units twice and we express acceleration in such units as mi.jhr. jsec. or ft.jsec.jsec. (ft. jsec2). Acceleration

change in velocity

=

time final velocity ( VI) - initial velocity ( Vi) time

VI - Vi t

For example, if a car traveling at the speed of 45 miles per hour accelerates until it reaches a speed of 60 miles per hour, in 5 seconds, its rate of acceleration will be 3 miles per hour per second.

A

=

VI - Vi

=

t

A= A=

( 60 mijhr - 45 mijhr ) 5 sec. 1 5 mijhr 5 sec. 3 mijhrjsec.

If the acceleration of an object decreases (negative acceleration or deceleration), the fol­ lowing formula is used to figure rate of de­ crease in velocity :

A

=

Vi - VI

t For example, if the engineer of a train trav­ eling at 8 0 miles per hour applies the brakes and reduces the train's speed to 40 miles per hour in 1 0 seconds, its decreased acceleration is 4 miles per hour per second .

A =

=

Vi - VI

t 40 mijhr 1 0 sec.

=

=

8 0 mijhr - 40 mijhr

1 0 sec. . 4 mljhrjsec

3. Freely Falling Bodies. In the 1 6th cen­ tury, Galileo, an Italian scientist, helped to discover that all bodies fall at the same rate regardless of their weight if the resistance of 62

the air is neglected. This means that in a vacuum a feather and a ten-pound weight will fall with the same speed. It is the gravitational attraction of the earth (pull of gravity) that causes all freely falling objects to be accel­ erated at the constant rate of 32 feet per sec­ ond per second. This figure varies in different places on the earth because the earth is not a perfect sphere. 4. Distance Covered by Moving Bodies. We can calculate the distance traveled by a rolling body which is uniformly accelerated by Llsing the formula s = t at2 in which s represents the distance, a the acceleration, and t the time traveled. However, when finding the distance traveled by a freely falling body, the formula becomes s = ! gt2 where g represents the acceleration due to gravity. Example:

How far will a car travel in five seconds if it is uniformly accelerated at the rate of 5 ft. j sec 2 ? s = t at� = -! ( 5 ft.jsec . 2 ) X ( 5 sec. ) 2 = -! ( 5 ft.jsec . 2 ) X 25 sec. = 2 . 5 ft. X 25 sec. = 62.5 ft. Example:

If an airplane dropped a bomb and it fell for 20 seconds, how far would it have fallen if we neglect air friction?

g s=t = t ( 32 ft.jsec . 2 ) = 1 6 ft. = 6400 ft.

X X ( 20 sec. ) 2 X 400 sec.

N EWTON'S LAWS OF MOTION

Sir Isaac Newton, a 1 7th-century English scientist, was extremely interested in the mo­ tion of objects. For years he observed the motions of the planets, did countless experi­ ments with falling objects, and studied the works of scientists who lived before his time. Finally, he published his ideas and conclusions which became known as Newton's Laws of Motion.

1. Newton's First Law of Motion - the Law of Inertia. This law states that a body at rest tends to remain at rest, while an object in uniform straight line motion will continue in this type of motion unless an outside un­ balanced force acts upon it. bnertia is a property of matter resulting from its mass that causes all bodies to resist any change in their state of being, whether at rest or in motion. In order to overcome the inertia of an object so as to produce or stop its mo­ tion or to change the magnitude or direction of its velocity, an unbalanced force must be ap­ plied to the object. For example, when you shovel snow the snow continues to move because of inertia even after the motion of the shovel has stopped. Your sudden lurch forward after a bus stops is caused by inertia. The need to ap­ ply a force to a hammer in space, even though the hammer is weightless, is due to inertia. If an object were set in motion in space, it would continue in a straight line motion forever un­ less some unbalanced force acted upon it. 2.. Newton's Second Law of Motion. New­ ton's First Law of Motion explained what would happen to an object if it were not acted upon by an unbalanced force. Newton's Sec­ ond Law of Motion goes a step farther and explains what happens to an object when an unbalanced force is applied to it. This law states that an unbalanced force acting on an object will produce an acceleration of the object proportional to the force and in the direction of the applied force. Thus, if the force applied to an object were doubled, "the acceleration of the object would double in the direction of the applied force. If, for example, you double the force with which you throw a baseball, you will double its acceleration. This law also implies that the acceleration of an object is inversely proportional to its mass. This relationship between acceleration, force and mass can be expressed mathematically : F a = - or F =

m

ma

As the mass of an object increases, its ac­ celeration decreases. In other words, a larger force is needed to accelerate a larger mass. A larger force, for example, is needed to throw a shotput than a baseball, and a larger force is needed to accelerate a truck than a jeep. If you were to hold a small rock in your hand, it would not hurt you, but if you were to catch the same rapidly moving rock, you might be injured. The difference between the two instances is that the moving rock possesses mo­ mentum. The momentum of an object is the product of its mass and its velocity. Momentum

=

m X v

An increase in either the mass or the veloc­ ity of an object results in an increased momen­ tum. A huge moving truck has a great momen­ tum because of its large mass. A large truck moving slowly may cause as much damage as a small automobile moving rapidly, if their mo­ mentums are equal. A small bullet shot from a gun also has a great momentum because of its high velocity. 3. Newton's Third Law of Motion. As you walk across the floor, your feet push against the floor; the floor exerts an equal and op­ posite force against your feet so that you can move. This phenomenon is explained by New­ ton's Third Law of Motion which states that for every action there is an equal and opposite reaction. According to the law, forces must al­ ways exist in pairs which are equal in magni­ tude (size) but opposite in direction. If this is true why then isn't every object in a continual state of equilibrium? The answer lies in the fact that the action and reaction never act on the same object. . .. �t� · "()�

.....a-..

:>

(�r(N> -. �

R/ t E

A C

··· A

C T

I �

��'I �ttS �

0

N

Effects of Newton's Third Law of Motion.

63

For example, when the air in an inflated balloon is suddenly released, the force of the moving air provides the action which propels the balloon forward. The reaction is the equal but opposite force of the escaping air pushing against the air molecules. Jet airplanes , rock­ ets, the recoil of a gun, and rotary lawn sprinklers are examples of machines based on Newton's Third Law of Motion.

Conservation of Momentum. When two ob­ jects are involved in an action-reaction situa­ tion and no other forces are present, the total momentum of these two objects remains un­ changed. For example, if an object exerts a force on a second object, the second body ex­ erts a force on the first object which is equal and opposite to the force exerted on it. This may be expressed mathematically : ml Vl = m2 V 2 In this equation m and v represent the mass and velocity of the two objects. If, for example, a 6-gram mass has a veloc­ ity of 2 cm. jsec. and it collides with a 4-gram mass, the velocity imparted to the 4-gram mass will be 3 cm./sec. and the resulting momen­ tums of the two objects will remain the same. m1 X V 1 = m2 X V i 6 g X 2 cm. /sec. = 4 g X V i 1 2 g-cm.jsec. = V 2 4g 3 cm. jsec. = V 2 The momentum of both masses immediately following the collision will be 1 2 g-cm./sec. The velocity imparted to the smaller mass ( 4 g ) was such as to make its momentum equal to the momentum of the larger mass

Materials: A textbook and a piece of notebook paper.

Procedure: 1. Stand the textbook across the extreme edge of the paper as seen in the illustration, and very slowly pull the paper out from under the book. 2. Moderately in=> 7 crease the force on / the paper. 3. Re-do the experiment but this time very quickly snap the paper from under the book. Observations: Record your observations for each of the procedures above.

1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Conclusions: Explain how Newton's Laws of Motion were involved in the above observations.

1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

( 6 g ) . All action-reaction situations thus in­ volve a transfer of momentums in such a way that the total momentum of the bodies re­ mains constant.

SELF-DISCOVERY ACTIVITY

Investigating an Example of Newton's Laws of Motion. 64

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R EVIEW TESTS Completion Questions

For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement. 1. Speed is a . . . . . . . . . . quantity since it has magnitude only. 2. An object traveling through space would travel in a . . . . . . . . . . . . . . . . . . . . . unless some . . . . . . . . . . . . . . . . . . . . . . . acted upon it. 3. If an object covers 1 0 feet every 5 seconds for 1 5 seconds, it would be undergoing

motion. 4. Why would a huge ship moving slowly have more momentum than a speeding bullet? . . . . . . .

5. Velocity is a vector quantity since it indicates . . . . . . . . . . . . as well as magnitude.

6. To avoid an accident, a man applies his brakes and decelerates from a speed of 50 miles per hour to 1 5 miles per hour in 7 seconds. What is his rate of deceleration? . . . . . . . . . . . . . . . . . . . 7. The laws of motion were developed by . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8. The pull of gravity causes all objects to fall with a constant acceleration of . . . . . . . . . . . . . .

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. . . . . . . . . . . . if air resistance is neglected. 9. An object dropped from the top of the Empire State Building falls for 9 seconds. How far will

it fall, neglecting air friction? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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10. An object is moving at a velocity of 50 ft./sec. How far will it travel in 20 seconds? .

travel in 20 seconds? . . . . . . . . . . . . .

11. Why could a person be thrown against the windshield of an automobile after a collision, if seat .

belts were not used? .

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65

12. The product of the mass and velocity is called . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13. According to Newton's Second Law of Motion, why would it be incorrect to state that a rocket is propelled forward by the force of escaping gases? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

14. According to Newton's Third Law of Motion, why doesn't a wall collapse when a small force is exerted upon it? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

15. How does Newton's Third Law of Motion explain how a rocket can be accelerated in space where there is no atmosphere? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

16. According to Newton's Third Law of Motion, forces always exist in . . . . . . . . . . . . . . . . . . . . . . 17. If a 25 g mass having a velocity of 6 em/sec collides with a 1 0 g mass, what is the velocity of .

the 1 0 g mass immediately following the collision? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

18. All action-reaction situations result in a transfer of forces in such a way as to conserve . . . . . . .

19. For every action there is an equal and opposite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.

.

. . . . . . . . . . . . . . . helped to discover that all bodies fall at the same rate regardless of their weight, if the resistance of air is neglected.

21. In order to change velocity a ( an ) . . . . . . . . . . . . . . force must be applied. 22. Why can a tiny meteor penetrate the metal hull of a space ship? . . . . . . . . . . . . . . . . . . . . . . .

.

23. What is inertia? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

24. An unbalanced force acting on an object will produce a (an ) . . . . . . . . . . . . . . . of the object

proportional to the force and in the direction of the applied force. 66

�A�E

_______

CLASS

J)ATE

______

__ __ __ __ __�__ __

25. Why will objects of different weIghts or shapes, dropped from a building, fall at different rates?

26. What is the acceleration of an airplane that takes 1 5 seconds to reach a velocity of 360 miles/hour after starting in a motionless position? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ,

27. All freely falling objects accelerate at a rate of 32 ft./sec. 2 because of . . . . . . . . . . . . . . . . . . . . .

.

28. If a 65-gram mass, traveling at a velocity of 1 0 centimeters/second, collides with an object and imparts a velocity of 8 em/sec to that object, what must the mass of the second object be? . . . .

29. According to the work done by Sir Isaac Newton, as the mass of an object increases, the accele.

.

property of matter due to its . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

ration of the object will

30. Inertia is

a

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Mu ltiple-Choice Questions In each .of the following questions, circle . t he letter preceding the word or phrase that best completes the statement or answers the question.

1. The rate at which an object moves in a given direction is called (c) magnitude, (d) velocity. 2. Which of the following units represents a measure of acceleration? ( c ) ft/sec2 , (d) ft/lb.

(a) speed,

( b ) motion,

(a) mi/hr,

3. All objects will fall at the same rate if they (a) are dropped from a great height, a vacuum, ( c ) have the same weight, (d) are equal in volume.

( b ) ft/sec

( b ) are in

4. In the first second of free fall an object will fall (a) 1 6 ft., ( b ) 32 ft., (c ) 64 ft., ( d) 8 ft.

5. Any object at rest possesses (a) momentum, ( b ) kinetic energy, (c) inertia, (d) acceleration. 6. An arrow released from a bow has great momentum because of its ( c) shape, (d) velocity.

(a) mass, ( b ) weight,

7. If a speedometer shows an increase of 5 mph every 5 seconds . for 5 seconds the automobile would be (a) accelerating, ( b ) in uniform motion, (c) changing velocity, (d) none of these answers.

8. In order to detect motion you need (a) a change in speed, ( b ) to be within the vehicle, ( c) to be isolated from all other objects, (d) a point of reference.

9. If a car traveling 30 miles per hour accelerated to 60 miles per hour in 2 seconds, its rate of acceleration is (a) 30 mi/hr, ( b ) 45 mi/hr/sec, (c) 35 mph, (d) 1 5 mi/hr/sec .

10. The recoil of a gun is an example of (a) Newton's First Law of Motion, ( b ) Newton's Second Law of Motion, ( c ) Newton's Third Law of Motion, Cd) Newton's Law of Gravity. NAME

_______

CLASS

.LJ DATE

_ _ _

_ _ _ _ _ _ _ _

67

M atching Q uestions In the space at the left of each item in Column A, place the letter of the term or expression in Column B that is most closely related to that item.

Column B

Column A

Newton's Second Law of Motion h. 32 ft/sec c. Galileo d. Newton's Third Law of Motion e. 32 ft/sec/sec f. Change of mass g. Equilibrium h. Change of velocity i. Motion j. Archimedes k. Uniform motion I. Acceleration m. Law of Inertia

1. Dense objects will fall to the earth in approxi-

Q.

mately the same time

2. Rotary lawn sprinkler 3. Usually causes a change In momentum 4. No unbalanced forces 5. Double the force, double the acceleration

6. The same distance traveled in the same time 7. Straight-line motion of an object in space. S. Acceleration of free falling objects, neglecting friction 9. Rate of change of velocity

10. Change in the position of an object

68

NAME

______

CLASS,

D �ATE

__ __ __

_ __ __ __ __ __ __ __

Chapter

8

ELECT R I C I TY STATIC E LECTRICITY

All matter is electrical in nature. You may have found this out when you walked across a dry wool rug and then touched a doorknob. Do you know why this happened? First let us discuss the basic nature of matter before we answer the question. The electrical nature of matter comes from its atomic structure. All matter is composed of atoms, the smallest particles of an element. Inside the nucleus of the atom are protons positively charged particles ; neutrons ­ neutral particles. Electrons are negatively charged particles that are found around the core: or nucleus of the atom. Since atoms normally have the same num­ ber of protons and electrons, matter is usually electrically neutral ; that is, it has no electrical charge. -

e_-_ ELECTRON

(-1

�If')IIMt:'Ii{---::-- NEUTRON (0)

The atom.

When two unlike materials rub together an electrical charge, either negative or posi­ tive, results. When you pass a hard rubber comb through your hair, some electrons move from your hair to the comb. The comb now has an excess of electrons and it becomes negatively charged. When a glass rod is stroked against a piece of silk, some of the electrons pass from the rod into the silk. The glass rod now has fewer electrons than protons and is positively charged. The production of an electric charge on an object is called electrification. According to the Law of Charges, unlike

_

_

_

rnllllillII 1I111111l1111iiillili

�

Z'-��, �� 'V '::-- � ,\\\ 1/ ,

-I!1 ..... .. :

;

.

'

.

\

EXCESS ELECTRONS ElECTRONS

GLASS ROD

�hr-�

Negative charge ­ comb.

,

- ,P

r, -- I

, - I

2-

II"", . ,

\

'"

DEFICIENCY OF

.

Positive charge glass rod.

charges attract each other and like charges repel each other. You felt the electric shock when you touched the doorknob because a large number of charges collected on the surface of your body, due to friction. These charges were opposite to those on the knob and caused a momentary discharge of electricity. Static electricity is the momentary transfer of electrons between unlike materials resulting from friction or contact. We can detect static electrical charges with an electroscope. This instrument consists of two very thin leaves of aluminum, tin foil or gold foil. The leaves are attached to one end of a metal rod which is insulated from the glass jar by a rubber stopper (see diagram ) . At the top of the rod is a metal knob.

Negatively charged electroscope. 69

When we bring an object having a static charge near the knob of the electroscope, the leaves spread apart (diverge ) . Why? Because each leaf, receiving the same charge, repels the other. If a negatively charged object is brought near the knob of a negatively charged electro­ scope, the leaves will spread even more. If the charge is positive, the leaves will come together. Why? Because the electrons will move from the leaves toward the object having fewer electrons.

Dangers of Static Electricity. The friction be­ tween air and water molecules against clouds causes a static charge. The bottom of a cloud is usually negatively charged ; the top is posi­ tively charged. As these charges build up, they finally become great enough to cause a huge discharge which we know as lightning. This giant spark is produced between a cloud and some other positively charged object such as the earth, a tree or another cloud. Never stand near trees during thunder­ storms - lightning is greatly attracted to them. Metal lightning rods on buildings pre­ vent lightning from striking them. The metal rods attract lightning and conduct the elec­ tricity harmlessly into the ground. Fires and explosions have often been caused by static electricity. The chain you see drag­ ging along the ground under gasoline trucks prevents sparks by carrying off excess static charges into the ground. Conveyor belts and the areas around toll booths are grounded to avoid electrical shocks to the attendant. Useful Applications of Static Electricity. Cott­ rell precipitators (electrostati c precipitators), are used in industry to remove harmful - and in some cases useful - particles escaping in smoke and dust. These particles are given an electrical charge and are then collected at an electrode having an opposite charge. The use of such devices in the manufacture of iron and steel and certain other industries help re­ duce air pollution. Van de Graaf generators produce large static charges which are used in atomic re70

search. They are also used to produce the high voltages needed to operate huge X-ray machines. SELF-DI SCOVERY ACTIVITY

Investigating the Law of Electric Charges. Materials: Two balloons, thread.

Procedure: 1. Inflate two balloons and suspend each by a piece of thread. 2. Rub each balloon briskly against some wool clothing. 3. Bring the two balloons close together and observe the effect. 4. Repeat step 2 with one of the balloons and place it against a wall. Observe the effect. Observations: 1. What did you observe in step

3?

2. What did you observe in step 4 ? . . . . .

Conclusions: Explain the above observations.

1. Step 3 : . . . . . . . . . . . . . . . . . . . . . . . .

.

2. Step 4 : . . . . . . . . . . . . . . . . . . . . . . . .

.

CU RRENT ELECTRICITY

\Vhen you use a toaster, vacuum cleaner or other electrical appliance in your home you are using current electricity. Current elec­ tricity, also called an "electric current," is a flow of electrons through a conductor. Any material that permits electrons to flow readily through it is a conductor. Some materials permit electrons to flow through them better than others. Silver is the best conductor; aluminum and copper are also excellent conductors. Most metals and carbon are good conductors of electric current. Non-metals, such as glass, cotton, rubber, ' mica and many plastics, do not permit elec­ trons to flow through them. These are called non-conductors or insulators. Fluids that con­ tain charged atoms or groups of atoms called ions can also conduct electricity. These are called electrolytic solutions or electrolytes. Static electricity is "electricity at rest" static means "stationary." Static electricity consists of electrical charges that have col­ lected on the surface of an object. Static electricity, therefore, contains potential or stored energy. Current electricity is "electricity in motion." It contains kinetic energy since the electrons are continuously moving through a conductor. In order to produce an electric current, elec­ trons must be made to move from one point in a conductor to another. In other words, work must be done to keep the electrons moving. In order to perform work, a force must be applied. Where does the force needed to produce and keep an electric current flowing come from? It usually comes from falling wa1ter, steam, gasoline, or diesel oil driving generators which convert mechanical energy into electrical energy. ­ .

U N ITS USED TO M EASURE ELECTRICITY

The Volt (V). The volt is a unit used to measure the force or pressure which pushes

electrons through the conductor. This force is often called the electromotive force (EMF) or the unit of potential difference. The term "potential difference" is used because a difference in potential energy must be maintained between the two points in a conductor in order for electrons to flow be­ tween these two points. The potential differ­ ence is built up and maintained by having fewer electrons at one point than at the other point. A voltmeter measures voltage.

The Ampere (A). This unit is used to measure the rate of current flow; that is, the number of electrons flowing past a given point in a conductor per second. An ammeter measures the number of amperes or amperage. When the electric current is weak a galvanometer is used to measure its strength. The Ohm (0). This unit measures the amount of resistance to the flow of electricity. The resistance of a conductor depends upon the following factors : ( a ) Length. The resistance varies directly as the length of the conductor ; that is, the longer the conductor, the greater the resistance. For example, if a 3 -ft. wire had a resistance of 1 0 ohms, a 6-ft. wire would have a resistance of 20 ohms. ( b ) Temperature. The resistance of most metals increases as the temperature increases. The resistance of carbon, many electrolytes and semiconductors decreases with an increase in tempera­ ture. Semiconductors are substances that behave as conductors or as insu­ lators depending upon conditions such as temperature. Transistors contain semiconductors such as germanium and silicon crystals and are used to replace vacuum tubes in electronic equipment. They are used because they are very small and create little heat. At cryogenic temperatures ( ex­ tremely low temperatures beginning at - 1 50° F ) , some poor conductors will become superconductors and some 71

nonconductors will become conduc­ tors . Superconductors are certain met­ als which become excellent conduc­ tors, that is, offer no resistance to the flow of current, at very low tempera­ tures. For example, lead is a supercon­ ductor at low temperatures. ( c ) Type of Material. Every substance has its own specific electrical resistance. Nichrome wire, for example, has a resistance that is 66 times greater than that of copper. Since high resistance results in the production of a large amount of heat, nichrome wire is often used in devices such as hot plates and toasters. ( d ) The Thickness (Diameter) of Wires. The resistance of a wire is affected by its diameter. A thick wire will have less resistance than thin wire of the same type. The resistance of a wire varies inversely as the cross-sectional area of the conductor. If a wire of 1 inch in diameter had a resistance of 20 ohms, the same type of wire with a 2-inch diameter would have a resis­ tance of 5 ohms.

Ohm's Law. This law states the relationship between current, electromotive force (poten­ tial difference) and resistance in an electric circuit. Ohm's Law states that the electrical current is directly proportional to the electro­ motive force in volts, and inversely propor­ tional to the resistance in ohms. In other words, the larger the voltage, the larger the current. The l arger the resistance, the smaller the cur­ rent. This may be expressed mathematically by the following formulas : I

= !!.... R

I

=

Rate of current in amperes.

E

=

Electromotive force in volts.

R

=

Resistance in ohms .

The following diagram will help you remem­ ber these formulas. Cover the letter of the factor you are trying to find. This letter 72

will represent one side of the formula you are trying to de­ termine. The two remaining letters, in the same positions they occupy in the pyramid, 4-_--1.__� will represent the other side of the formula.

Example: ( a ) What is the rate of current flow through a conductor having a resistance of 20 ohms if it is connected to a 1 20volt line? I

=E

1 20 V

= 6 amps. 20 n ( b ) How much voltage is needed to pro­ duce a current flow of 3 amperes through a resistance of 200 ohms?

E

-

R

=

lR

=

=

--

3A X 200 n

=

600 volts

( c ) How much resistance is produced if a current of 4 amperes is sent through a line having a voltage of 1 20?

R=

�= I

1 20V

=

4A

30 n

E LECTRICAL CIRCUITS

Series Circuits. In a series circuit the electrons follow only one path. They leave one terminal and flow through all the electrical devices one after the other before they go back to the second terminal of the source. There are no other paths through which these electrons can flow. RESISTER (BULB) \

1 /

A series circuit.

The main characteristics of a series circuit: 1. Current. The current is the same in

every part of the series circuit. If one bulb in a series circuit containing more than one bulb burns out or is removed, the circuit is broken and all the bulbs go out.

1 . What is the total resistance?

2.. Resistance. What happens when you add more bulbs to a series circuit? You are adding more resistances, causing the flow of cument to decrease. This will cause the bulbs to dim. We say that the total resistance of a series circuit is equal to the sum of the indi­ vidual resistances and is, therefore, always greater than any single individual resistance. As an equation :

2. What is the voltage drop at r1?

R

= r1

+

r2

+

r3

4. What is the total voltage drop?

. . .

3" Voltage Drop. The voltage in a series circuit is divided among all electrical resist­ ances in the circuit. As the voltage travels across the resistors, the voltage drops. The voltage drop is greatest across the highest resistance. Ohm's Law is used to calculate the voltage drop for each resistance :

IR

E Voltage drop

3. What is the voltage drop at r2?

The total voltage drop of a series circuit is equal to the sum of the individual voltage drops.

Parallel Circuits. In a parallel circuit the electrons may follow separate and complete paths. The devices in the circuit are connected side by side, permitting the current to divide and flow through the resistances at the same time. This diagram of a parallel circuit shows three resistances connected in parallel. I

e,

==

VOLTAGE DROP AT

r,

e.

=

VOLTAGE DROP AT ,

I

/

/

r.

A parallel circuit.

TO POWER SOURCE

A series circuit.

In this drawing of a series circuit the current is 2 amps in all parts of the circuit.

The main characteristics of a parallel cir­ cuit are : 1. Current. The current in the parallel circuit varies and is divided among the re­ sistances. The greatest current is in the smallest 73

resistance. The total current is the sum of the current in the individual branches : I

=

i1

+ i2 + is

. . .

3. Voltage Drop. The voltage across each branch in a parallel circuit is the same. There­ fore, the voltage of the circuit remains constant.

E

= e1 = e2 = es

•

.

•

If one bulb in a parallel circuit burns out, the rest will remain lighted since there are al­ ternate pathways for the flow of electrons and, thus, the circuit remains completed. 2. Resistance. The total resistance of a parallel circuit is always less than that of the smallest resistance. Each new resistance rep­ resents a new pathway for electrons and reduces the total resistance of the circuit. This happens because each resistance acts also as a conductor. If all the resistances have the same value, the total resistance of the circuit may be determined by the following formula :

R = !...

Study the above drawing of a parallel cir­ cuit. Solve the following : 1 . What is the current through r1?

2. What is the current through r2?

n (number of resistances )

Example :

If six 1 2-ohm resistances are connected to­ gether in a parallel circuit, the total resistance would be 2 ohms.

R=

12 6

n=2n

3 . What is the total current?

4 . What is the total resistance?

If the resistances have different values, the following formula is used to calculate the total resistance of the circuit.

If a 3-ohm resistance and a 6-ohm resist­ ance are connected in parallel, the total re­ sistance will be 2 ohms.

1

1

1

R - 3Q + 6"n 1

3

1 or 6 2

R R=2n -

74

=

-

Note that the total resistance of a number of resistances in a parallel circuit is always less than that of the smallest resistance. This helps you check your answer.

3" Voltage Drop. The voltage in a parallel circuit remains constant. In this circuit it is 1 2 volts. TO DRY CELL

POWER AND E N ERGY

The movement of an electric current rep­ resents a form of kinetic energy. This energy is often used as a force to do work. Electrical power is the rate at which electrical energy is converted to work. The unit used to express electrical power is the watt (W). Power in Watts = Volts X Amperes X A W= V One watt of electrical power is equivalent to the work done when one ampere flows under a pressure of one volt. Electrical power is usually measured in kilowatts. As you have learned, kilo means 1 000; therefore, 1 kilo­ watt ( l kw. ) is equal to 1 000 watts. For example, if an electric light were plugged into a 1 20V circuit and the rate of current flow was .5 amps, the lamp would produce 60 watts of electrical power.

W = V X A W = 1 20 volts X . 5 amp W = 60 watts

TO DRY CELL

Series and parallel circuits.

3. Connect to the dry cell and loosen a bulb in the parallel circuit. Observe the results. 4. Replace one of the bulbs in the series circuit with a l . 5v bulb and observe the results. 5. Replace one of the bulbs in the parallel circuit with a 1 . 5v bulb and observe the results.

Observations: Record observations below.

1. Step 2 : . . . . . . . . . . . . . . . . . . . . . . . . .

2. Step 3 : . . . . . . . . . . . . . . . . . . . . . . . .

.

3. Step 4: . . . . . . . . . . . . . . . . . . . . . . . .

.

4. Step 5 : . . . . . . . . . . . . . . . . . . . . . . . .

.

S ELF-DI SCOVERY ACTIVITY InvEistigating Parallel and Series Circuits.

Ma1:erials: Four screw-base miniature lamp sockets, four 2.S-volt bulbs, one 1 . S -volt bulb, insulated wire, two switches, a board 1 � , X 1 � ', large 1 . S-volt dry cell.

Prol�edure: 1 . Connect two 2 . 5 volt bulbs in series and two 2 .5 volt bulbs in parallel as shown in the diagram. 2. After connecting the series circuit to the dry cell, throw the switch. Then loosen a bulb in the series circuit and observe the results.

Conclusions: 1. Explain the results observed when one bulb was loosened in a series circuit. . . . . .

. . . . . . . . . . . .. . .. .

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75

2. Explain the results observed when one

bulb was loosened in a parallel circuit. . . . .

3. Explain the results observed when a

4. Explain the results observed when a

60W bulb was inserted into the series circuit.

60W bulb was inserted into a parallel circuit.

76

R EVIEW TESTS Completion Questions For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement. 1. Static electricity is pruduced by . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

2. Matter is usually electrically . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

3. Objects which have a deficiency of electrons are said to possess a . . . . . . . . . . . . . . . . . charge. 4. Why would a rubber comb rubbed through your hair attract small pieces of paper? . . . . . . . .

.

.

6. The production of an electric charge on an object is called . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

5. What is static electricity?

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7. If an electroscope were negatively charged and a positively charged object were brought near the knob, what would happen to the leaves? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

8. As the diameter of a wire increases, its resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

9. Explain how clouds become electrically charged . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

10. Toll booths and conveyor belts are . . . . . . . . . . . . . . . . . . . . . . . . . . . . . to prevent electrical shocks. 11. In the space at the right, complete the diagram illustrating how you would connect the two dry cell batteries in series and parallel circuits.

NAME

rl

rl

rl

Parallel circuit.

Series circuit. CLASS

DATE

rl

77

12. Fill

III

the following chart with the correct information:

Pa thways

Parallel Circui t

Series Circui t

Current

Total Resistance

Voltage Drop

i3. Why are houses wired in parallel instead of series?

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14. Answer the following questions concerning the diagram at the right :

(a) What type of circuit is it? . . . . . . . . . . . . . . . . . . ( b ) What is the voltage of the following : r1 . . . . . . . . r2 . . . . . . .

.

(c) What is the current flowing through the 30

n

resistor?

(d) What is the total resistance of the circuit?

( e ) What is the total current in the circuit? . . . . .

78

.

NAME._______CLASS

D ...... ATE

_ _ _

_ _ _ _ _ _ _ _

15. Answer the following questions concerning this diagram : ( a ) What type of circuit is it? . . . . . . . . . . . . . . . .

( b ) What is the current flow at A2? . . . . . . . .

.

.

50

.

( c ) What is the total resistance of the circuit?

(

,

(d) What is the voltage drop across the 5 ohm resistor?

. . . . . . . . . . .. . .. . .. . . . ......... . . .

.

( e ) What is the voltage drop across the 1 0 ohm re. . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . .:

sistor?

(f) What is the total voltage drop of the circuit?

16. The rate of converting electrical energy into work is called . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17. 200 kw equals . . . . . . . . . . . . . . . . watts. 18. How many watts are produced in a 1 20V circuit which has 3 amps flowing through it? 19. A . . . . . . . . . . . . . . . . . . can be used to detect the strength and direction of a small electric current. 20. Some poor conductors of electricity may become superconductors at temperatures below - 1 50 ° F. Such temperatures are called . . . . . . . . . . . . . . . temperatures.

21. A Van de Graaf generator produces huge . . . . . . . . . charges useful in atomic research. 22. Lightning rods on buildings attract lightning and carry the electricity harmlessly into the . . . . . . . . . 23. Why is copper used in electrical wire? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(a)

24. List three examples of electrical insulators. (c)

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Mu ltiple-Choice Questions In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question.

1. The negatively charged particles spinning around the nucleus of an atom are the (a) protons, ( b ) electrons, (c) neutrons, (d) shells. 2. A device which can be used to detect the type of a small static charge is a ( an ) (a) galvanometer, ( b ) ammeter, ( c ) - voltmeter, (d) electroscope. NAME

_______

CLASS

...... ATE, D

_ _ _

_ _ _ _ _ _ _ _

79

3. The unit used to measure the electromotive force or potential difference is the (a) volt, (b) ampere, (c ) ohm, ( d ) watt. 4. Five 50-ohm lamps connected in parallel would have a combined resistance of (a) 50, ( b ) 55, (c) 250, ( d ) 1 0 ohms. 5. A non-metal which is carbon .

a

good conductor of electricity is ( a ) rubber, ( b ) aluminum, (c) plastic, (d)

6. The best electrical conductor under normal conditions is (a) copper, ( b ) glass, (c ) silver, (d) aluminum.

7. Static electricity might best be compared to ( c ) kinetic energy, ( d ) atomic energy.

(a) potential energy,

( b ) chemical energy,

8. Substances that may behave as a conductor or an insulator under certain conditions are called (a) crystals, ( b ) semiconductors, (c) electrolytes, (d) resistors. 9. If an appliance having a resistance of 20 ohms were plugged into your household current, the rate of current flow would be ( a ) 3, ( b ) 2400, (c) 20, ( d ) 6 amperes. 10. The electrical charge of the nucleus of an atom is ( d ) varies.

(a) positive,

( b ) negative,

(c) zero,

Matching Questions In the space at the left of each item in Column A, place the letter of the term or expression in Column B that is most closely related to that item.

Column B

Column A

a. Path traveled by electrons b . Aluminum c. Ammeter

1. Create little heat, small, replacing vacuum tubes 2. High resistance to electrical current

3. Solution capable of conducting an electrical current 4. Static electricity

5. A device to measure the rate of current flow 6. Electrical power 7. Energy level, rings, shell or orbit 8. Prevents a spark due to static electricity 9. Removes annoying and, in some cases, useful ma­

d. Nichrome e . Friction f· Trees g. Voltmeter h. Transistors i . Cottrell precipitator j. Electrolyte k. Carbon I. Chains on a gasoline truck m. Watt

terial from smoke, thus helping to reduce air pollution

. . . . . . . . 10. Avoid during thunder and electrical storms

80

NAME,

_______

CLASS

D ....... ATE

___

_ _ _ _ _ _ _ _

Chapter

9

M AG N ET I S M MAGN ETS

For thousands of years man has known that certain substances had the power to attract certain other substances. Early man discov­ ered that certain black "rocks" had magnetic properties. These were natural magnets, called lodestones, which contain an iron ore, mag­ netite.

Typ1es of Magnets. Magnets found in nature are called natural magnets. Magnets made by man from iron or steel are called artificial magnets. There are two types of artificial mag­ nets" temporary and permanent. Temporary magnets, commonly made of soft iron, keep their magnetic properties for a short time. Permanent magnets, made of iron, steel or steel alloys such as alnico, keep their magnetism for a long time. Magnetic Fields. We can't see, smell, hear, feel, or even touch magnetism because it is in­ visible; but it does exist. Around every magnet is a region in which the magnetic effects exist. This area, known as the magnetic field, con­ tains invisible magnetic lines of force. You can see these lines of force by -placing a bar magnet under a piece of glass and sprink­ ling iron filings on the glass above the magnet. The pattern that forms shows that the mag­ netk lines of force are concentrated at the op­ posite ends of the magnet called the poles of the magnet. Poles of a Magnet. One end of the magnet is the positive or north pole ( N-pole ) . If a bar magnet is suspended so that it rotates freely, it will finally stop with the N-pole always point­ ing to the earth's magnetic pole (near the earth's geographic north pole). The other end of the magnet, the negative or south pole (S-pole) always points toward the earth's south magnetic pole.

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Law of Magnetic Poles. This law states that like magnetic poles repel each other and unlike magnetic poles attract each other. If you bring the N-poles of two magnets together, you will see that they repel each other. Bring the N­ and S-po1es of two magnets together and they will attract each other. The Law of Magnetic Poles is similar to the Law of Electrical Charges. Theory of Magnetism. No one has definitely explained the cause of magnetism. Many sci­ entists believe that magnetic properties are re­ lated to the fact that electrons in an atom spin on their own axis at the same time that they orbit the nucleus (similar to our earth's move­ ment around the sun ) . These spinning motions produce magnetic fields, If these magnetic

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REVOLUTION

Spinning electron produces a magnetic field.

fields are not neutralized within the atom, the atoms behave like tiny magnets and are called 81

dipoles. In magnetic substances these dipoles are arranged into magnetic regions called do­ mains in which the north or (+) poles of all the dipoles face in one direction and the south or (-) poles face in the opposite direction.

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You can magnetize a piece of iron or steel, such as a knitting needle, by stroking it in one direction a number of times with one end of a bar magnet. This causes the dipoles to line up into domains. This is the contact method of making a magnet . In the induction method you don't have to touch the object to the magnet. If you place a nail in the magnetic field of a bar magnet the nail will become magnetized. When you with­ draw the nail it will lose its magnetism. If you heat or hammer a magnet you will disarrange the domains and destroy its mag­ netic properties.

Electromagnets. The electromagnet is a tem­ porary magnet consisting of a current-carrying wire wound around a core. A Danish physicist, Hans Oersted, discovered that when an electric current is passed through a wire it will produce a magnetic field around it. Joseph Henry, an American scientist, produced the first electro­ magnet. Powerful electromagnets are used to lift heavy iron and steel objects. Electrical de­ vices such as doorbells, telephones, telegraphs, radios, phonographs, motors and generators use electromagnets. The betatron, an atom­ smashing machine, uses a giant electromagnet. SELF-DI SCOVERY ACTIVITY Making an Electromagnet

Materials: A dry cell, some insulated bell wire, scissors, 82

a large iron nail, and some small items of iron or steel to test.

Procedure: 1. Wrap about 50 turns of the insulated bell wire around the nail. 2. Remove the insulation from the ends of the wire.

3. Connect the ends to the dry cell as shown in the illustration.

BATTERY WIRE COilS A simple electromagnet.

Observations: 1. Test your electromagnet with some of the small iron and steel items you collected. What do you observe? . . . . . . . . . . . . . . . . . . . . . .

.

2. Disconnect the wire from the dry cell. Now try to pick up the items. What do you

observe? . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

3. Can you think of some ways you might make your electromagnet more powerful? Try them and find out if you are right. What are your results? . . . . . . . . . . . . . . . . . . . . . . . . . .

G E N E RATORS

The generator is a machine that changes mechanical energy into electrical energy. Mi­ cha.�1 Faraday, an English scientist, discovered the principle upon which the generator oper­ ates A n electric current is produced in a con­ ductor forming part of a closed circuit when the conductor moves so that it cuts the lines of force of a magnetic field. A current that is produced in this way is said to be an induced (caused) current. ..

Production of an induced current. The direction of the current alternates as the movement of the magnet is reversed.

The magnet provides the force necessary to do the work in moving the electrons through t e conductor. In order to cut the magnetic lmes of force, either the magnet or the con­ ductor may be moved. If, for example, the con­ ductor is a coil of wire, a current may be in­ duced in the wire by moving a magnet through the coil. The circuit may be completed by con­ necting it to a galvanometer (an instrument for detecting small electric currents) to measure the strength and direction of the current. When the magnet is pushed into the coil (arrow B) the needle on the galvanometer �wings in one direction (A) . When the magnet IS wllthdrawn (arrow A), the needle swings in the opposite direction (B). This shows that the direction of the flow of current has been re­ versed.

�

Typ.�s of Electrical Currents. There are two types of electrical currents: ( 1 ) alternating (AC), and (2) direct (DC).

In alternating currents (AC) the electrons constantly reverse their direction of flow. The advantages of AC current are that ( 1) its volt­ age can easily be raised or lowered as needed by a transformer, and (2) it can be sent long distances at high voltage with little loss of elec­ tricity due to heat caused by friction. In direct current (DC) the electrons flow in one direction only. Direct current is produced by the generator of an automobile when the motor is running. It supplies the current for the lights, horn and other equipment and also charges the storage battery. Electro­ plating, a process in which metals are coated with other metals, uses direct current.

The AC Generator. The AC generator con­ sists of ( 1 ) an armature, (2) field magnets, (3) slip rings, and (4) brushes. The armature is a large coil of wire wound around a core of soft iron. The core is mounted on an axle which permits it to rotate in the magnetic field. The field magnets have opposite poles which provide the magnetic field. The slip rings, two brass rings connected to the armature, conduct the current from the armature to the brushes. The carbon or metal brushes conduct the cur­ rent from the slip rings to the wires. The wires carry the electricity to the outside circuit. To simplify our discussion we will consider the armature as having only one loop of wire. As the armature turns on its axle, the coil of wire cuts the lines of force of the magnetic field between the field magnets. This causes a cur­ rent to be induced in the coil.

BRUSH ______ AC GALVANOMETER .J

generator.

83

During one-half of the rotation of the loop, the voltage ( electromotive force, or EMF) in­ duced in the armature rises until the greatest number of magnetic lines of force are cut by the loop. During the other half of the rotation, the induced voltage builds up to a maximum, but the direction of the current is reversed. Why? Because the loop cuts the lines of force in the opposite direction. The greatest voltage is induced when the loop is in a horizontal position because at this time the most lines of force are cut. When the loop is in a vertical position no lines of mag­ netic force are cut. Thus, the induced voltage at that moment is zero.

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A complete rotation of the coil, called the cycle, requires 360 0 • The electrons of an al­ ternating current travel back and forth in the circuit once during a cycle. The number of cycles per second is called frequency. The elec­ tricity sent into your home has a frequency of 60 cycles every second and a voltage (electro­ motive force or EMF) of 1 20. The current produced by a generator may be increased by ( 1 ) increasing the speed of rot
Direct current generators have the same parts as alternating current generators except that there is a single split ring. The split ring, called a commutator, consists of a ring split into two halves insulated from each other. Although an alternating current is induced in the armature of a direct current generator, the commutator changes the AC current to DC current in this way: as the induced cur­ rent in the armature (AC) is about to reverse its direction of flow at the end of a half rotation (cycle), the rotating halves of the split ring commutator change brushes. As a result, the brushes keep the same electrical charge and the current entering the external circuit flows in only one direction (DC ) .

E LECTR IC M OTORS

An electric motor changes electrical energy into mechanical energy. The simple DC motor consists of the same parts as the DC generator. The operation of the DC motor is the reverse of the DC generator. Instead of drawing elec­ tricity from the armature, electricity is sent to both a single field magnet and the armature. The current produces magnetic fields around the field magnet and the armature. According to the law of magnetic poles, unlike magnetic poles repel each other. Since the armature is essentially an electro­ magnet free to rotate, the repulsion of the like poles causes the armature to begin to turn. When the north and south poles of the field magnet and armature are directly opposite each other, motion, of course, would stop since opposite magnetic poles attract each other. To prevent any stoppage in rotation of the armature, a commutator and brushes are used to change the direction of the current in the armature at j ust the correct moment. This change of current flow causes the magnetic polarity of the armature to reverse, causing another repulsion which keeps the armature turning. Motors and generators are also some­ times called dynamos.

N TO DRY CELL COMMUTATOR ARMATURE The DC motor. 1. Both the armature and the field magnet become electromagnets as electricity flows through them. 2. The armature rotates because of repulsion of like poles and attraction of unlike poles. The force of inertia carries the poles slightly beyond the point where like poles exactly face each other.

3 . The commutator shifts from one brush to the other, thus reversing the polarity of the armature. As a result, the pole of the armature and field magnet are now the same. 4. Repulsion of like poles and attraction of unlike poles causes the rotation of the armature to continue.

S ELF-D ISCOVERY ACTIVITY

3. Bring both portions of the coil together and repeat step 2 (Diagram B). Record your observation.

Usinlg a Magnet to Induce an Electric Current

Mab�rials: Coil of bell wire, two bar magnets, and a galvanometer.

Procedure: 1. Unwind about 1 2 coils of bell wire and connect the ends to a galvanometer. ( Diagram A). 2. Insert the N-pole of the bar magnet into the right-hand side of the coil. Observe the galvanometer and place your results in the chart on the next page.

Inducing an electric

CUi rent.

4. Stop the motion of the magnet while it is within the coil and record your observation.

85

5. Withdraw the magnet from the coil. Record your observations. 6. Keep the magnet stationary and move the coil back and forth over the magnet. Re­ cord your observations. 7. Shove the magnet into and pull it out of the coil, gradually increasing its speed. Re­ cord the results. 8. Repeat step 7 using two bar magnets tied together, north pole to north pole. Record your results.

1. How is the electricity induced in the conductor?

. . . . . . . . .. . . . . . . . . . . . . . . . . . . .

2. In what ways can the current be in-

creased? . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Observations: Procedure

Conclusions:

Galvanometer Direction Reading

2.

3. What objects may be moved to induce a 3.

current? . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4. 5. 6. 7.

8.

86

4. What type of electricity was induced?

Explain why. . . .

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REVIEW TESTS Completion Questions For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement. 1. An iron ore called . . . . . . . . . . . . . is an example of a natural magnet.

2.

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. . . . . . . . . . . . magnets are usually made of steel or some steel aIloys.

3. Where are the magnetic lines of force concentrated? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4. The spinning motions of the . . . . . . . . . . . . in an atom may produce a magnetic field.

5. What is a dipole? .

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7. What are the advantages of an electromagnet compared to a permanent magnet? . . . . . . . . . . .

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6. What is the basic principle upon which the electromagnet operates?

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8. How could you make a needle into a magnet? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9. In a magnet the dipoles are arranged into magnetic regions called . . . . . . . . . . . . . . . . . . . . . . . . 10. List three ways in which electromagnets are used.

(a) (b) (c)

11. How are the dipoles arranged in a magnet? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

NAME

��_____� ____

CLASS

---.-DA TE.

___

_ _ _ _ _ _ _ _

.

87

12. Why does heating a magnet destroy its magnetic properties? . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13. What is the major principle upon which a generator operates? . . . . . . . . . . . . . . . . . . . . . . . . . . .

14. Who developed the above principle? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15. List three ways in which the strength of a current produced by a generator can be increased: .

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(c) 16. The electricity sent to your home has a frequency of . . . . cycles every second. 17. What is direct current? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

18. A motor converts electricity into . . . . . . . . . . . . . . . energy. 19. Stationary armatures in huge industrial AC generators are called 20. The . . . . . . . . . in a generator carry the current to the wires leading to the external circuit. 21.

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can be made visible by lightly sprinkling iron filings over

a piece of glass resting upon a bar magnet.

22. The south pole of a magnet is also known as the . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23. List three factors upon which the strength of an electromagnet depends. (a )

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(b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

24. In a direct current generator, the . . . . . . . . . . . . . . . changes alternating current to direct current. 25. In alternating current, each cycle requires a rotation of . . . . . . . . . . . . . . . on the part of the coil. 88

NAML .

__ _ _ _ __

.____

CLASS

D.. ATE ....

_ _ _

_ _ _ _ _ _ _ _

M ultiple-Choice Questions

In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question. 1. A natural-occurring magnet is called a ( an ) ( d) electromagnet.

( a ) iron ore, ( b ) artificial magnet, (c) lodestone,

2. Temporary magnets are commonly made of ( a ) steel, ( b ) alnico, (c) copper, (d) soft iron.

3. Which of the following abbreviations stands for an electrical current in which the electrons reverse their directions? ( a ) Be, ( b ) DC, (c) AC, (d) EMF. 4. Which of the following is an example of a type of dynamo? ( a ) galvanometer, ( b ) transformer, (c) magnet, (d) generator. 5. Which of the following is found in a direct current generator but not in an alternating current generator? ( a ) commutator, ( b ) brush, ( c ) slip ring, (d) magnet.

6. The north pole of a magnet always points to the (a ) geographical north pole, ( b ) geographical south pole, Cc) magnetic north pole, Cd) magnetic south pole. 7. The law of magnetic poles is most similar to the law of ( c ) inertia, (d) conservation of matter and energy.

( a ) gravity,

( b ) electrical charges,

8. As a motor operates, a magnetic field is produced around the field magnet and the (a) armature, ( b ) brush, ( c ) housing, (d) pulley.

9. In the United States, household voltage is usually ( a ) 60 volts, ( b ) 90 volts, (c) 1 20 volts, ( d ) 400 volts.

10. Structures which have to be replaced because of wear as they press against the rotating slip ring or commutator are the ( a ) field magnets, ( b ) wires, ( c ) bearings, (d) brushes. 1 1.-15. These questions concern the diagram of the bell at the right.

ARMATURE,

PUSH BUTTON r-----( 0 )--..,

11. In the diagram, the circuit is completed when the button is pushed. Which of the following statements describes what happens after the button is pushed? ( a ) The armature will be repelled. ( b ) The current will flow constantly. (c) The armature will be attracted. (d) The current will not flow at all . 12. If the battery wires in the diagram of the bell were reversed ( a ) it would make no difference in ring­ ing the bell, ( b ) the clapper would strike the bell more often, ( c ) the clapper would strike the bell less often, (d) the bell would not ring.

BATTERY

13. When the button of the bell was pushed, the bell could barely be heard. The strength of the spring was then increased to make it stiffer. Now the bell will (a) probably not ring at all, ( b ) prob­ ably ring louder, ( c ) probably not ring as often, (d) probably ring more frequently. 14. If the contact screw were turned so that it no longer touched the spring, which of the following NAME

____ _

CLASS

___

DATE

_ _ _ _ _ _ _ _

89

statements will be true? (a) the bell will continue to ring as before, ( b ) the bell will not ring, (c) the bell will ring louder than before, (d) the bell will ring softer than before.

15. If the number of turns of wire of the electromagnet in the bell were increased, the bell will ( a ) no longer ring, (b) ring louder, (c) ring softer, ( d ) not be affected.

Matching Questions In the space at the left of each item in Column A, place the letter of the term or expression in Column B that is most closely related to that item.

Column A

Column B

a. Transformer

1. Electroplating

b . Makes use of direct current c. Sending electricity long dis-

2. Coil of wire in a generator or motor

tances at high voltage d. Core of a magnet e. Armature f. Galvanometer g. Joseph Henry h. Commutator or split ring i. Hans Oersted j. Maximum voltage k. Slip ring I. Makes use of alternating current m. Alnico

3. An electrical current passed through a wire will produce a magnetic field around the wire

4. Converts AC to DC 5. Prevents loss of electricity due to friction

6. A magnetic alloy 7. An instrument used to detect electrical currents

8. Device used to increase or decrease voltage 9. Greatest number of magnetic lines of force are cut by a rotating armature of a gen­ ator

. . . . . . . . 10. Absorbs and concentrates magnetic lines of force

90

NAME

______

CLASS

DATE

___

_____ _ _ _

Chapter

10

SOU N D What is sound? To some it is the rustle of a leaf in the wind. To others it is the roar of a lion , or the clap of thunder, or the sonic boom of a jet plane as it crashes through the sound barrier. Sound is all these things and more, as we shall see. SELF-DISCOVERY ACTIVITY Whalt Causes Sound?

MatfdaIs: A tuning fork, thread, masking tape, ping­ pong ball, and tumbler of water.

Procledure: 1. Attach the thread to the ping-pong ball with the tape. 2. Strike the tuning fork with a solid object and hold it against the ping-pong ball. Observe the tuning fork and the ball carefully.

3. Strike the tuning fork again. Insert the tines of the fork into the tumbler of water. Observe.

Observations: 1. What happened to the ping-pong ball when you touched it against the tuning fork?

2. Based on your observations, what causes

sound? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

How Is Sound Transmitted? In order for us to hear sound the vibrations must be trans­ mitted to our ears and passed on to the brain where the sound is interpreted . In most cases, vibrations are transmitted by air molecules, which have been set in motion by the vibra­ tions. Solids and liquids are better conductors of sound than gases. In solids and liquids the molecules are closer together than in gases, thus making it easier for the vibrations to move from one molecule to the next. Sound cannot be transmitted in a vacuum because there are no molecules which can be made to vibrate. Sound Waves. Whenever an object vibrates it causes the air around it to vibrate also. These vibrations spread out and travel as pulses or waves called sound waves. Sound waves are JongitudinaJ waves in COMPR£SSION

, �

L,RAREFACTION

�

:

MO' N OF MOLECULE DIRECTION OF WAVE

Sound - a longitudinal wave.

(Molecules move parallel to the direCtion of the wave.)

2. What happened to the water in the tum-

bler when you inserted the fork? . . . . . . . . . . .

Conclusions: 1 . What kind of motion would be necessary to cause the effects you observed above? . . . . .

which the molecules vibrate back and forth parallel to the direction in which the wave is traveling. In such a wave, the molecules do not actually travel; they merely vibrate. Sound waves are made up of two parts : ( 1 ) the compression, and ( 2 ) the rarefaction. As the vibrations move through the air, the forward vibration of the molecules causes the molecules ahead to be pushed close together, or compressed. This is the compression part. 91

When the molecules vibrate backward, they become spread further apart, or rarefied. This is the rarefaction part. Alternate compressions ( condensations ) and rarefactions follow each other as fast as the medium vibrates.

Characteristics of a Sound Wave. There are three major factors to consider when we dis­ cuss sound waves : 1. Frequency. The number of vibrations made by a vibrating object in one second is called its frequency. Frequency of a vibrating body is expressed as vibrations per second ( v.p.s. ) . WAVE LENGTH

Frequency. This curve represents the energy of the particle i n a wave, not the movement of the particle itself.

2. Wave Length. The distance from the crest of one wave to the crest of the next wave is called its wave length. Wave length is expressed in feet or meters and has the symbol I or A. As the frequency of a wave in­ creases, the wave length decreases.

3. The amplitude of a wave is the maximum distance that the particle in a wave will move, or the distance between the crest and trough of the same wave.

Velocity of Sound. The speed of sound de­ pends upon the medium it passes through, and the temperature. For example, sound travels approximately 1 5 times faster in steel than in air. Sound travels faster at higher temperatures . At normal room temperature sound will travel at about 1 1 3 0 feet per sec­ ond. At 0° C. ( 3 2 0 F. ) , sound will travel at 1 090 ft./sec. The velocity of sound in air increases by 2 ft./sec. for each degree of increase in the Centigrade temperature. To compute the velocity of sound in air we use the following formul a : 92

v

=

1 090 + 2 ( Co . )

For example, the velocity of sound at 40° C. is 1 1 70 ft./sec. V V

= =

1 090 + 2 ( 40 ) 1 1 70 ft./sec.

The velocity of sound in air ( 1 1 00 ft./sec. or 74 1 miles per hour) is called Mach 1, after Ernst Mach, an Austrian physicist. Velocities higher than this are supersonic velocities. An airplane traveling at twice the speed of sound is said to be traveling at Mach 2 . A s a n airplane approaches the speed of sound, powerful compression waves increase the density of the air in front of the plane. These waves form a sonic barrier which the aircraft must travel through as it exceeds the speed of sound. When this occurs, a shock wave is formed around the aircraft. The shock wave may be powerful enough to shake a house and break windows. Ultrasonic vibrations are those above 20,000 vibrations per second. Most people can normally hear sounds ranging from · 1 6 vibrations per second to about 20,000 vibra­ tions per second. Many animals, such as dogs, can hear above this range. Dog whistles, which the human cannot hear, vibrate up to 1 00,000 vibrations per second.

The Pitch of Sound. The pitch of sound refers to the frequency of high or low tones. Pitch depends upon frequency - the higher the frequency, the higher the pitch. Thus, a person with a high-pitched voice is producing sound waves having a greater frequency than a person with a low-pitched voice. The faster a siren is turned, the greater will be its fre­ quency and, therefore, the higher the pitch of the sound it produces.

Low pitch. High pitch.

The Loudness of Sound. The loudness of a sound depends primarily upon the amplitude, or height of the sound wave. A greater ampli­ tude produces a louder sound. For example,

Soft.

AMPLITUDE� Loud.

1

if a violin string is plucked gently, a soft sound is produced, but if the string is plucked vio­ lently, a loud sound results. Loudness is usually measured in units called decibels.

The Reflection of Sound (Echoes). Sound waves may be reflected. For example, if you shout in the direction of a wall some distance away, the sound will come back to you. The reflected sounds are called echoes. These echoes are caused by the reflection of sound waves by a relatively smooth surface. The reflection of sound may be undesirable, as in a concert hall or an auditorium. On the other hand, it may be useful, as in sonar which is an application of ultrasonic vibrations which are reflected off underwater objects . These reflec­ tions enable men in submarines, for example, to detect, locate and determine the nature of underwater objects and to map the ocean floor. In small rooms, echoes may not be heard because the sound hits the wall and bounces back quickly. This occurs so rapidly that the echo and the original sound will almost merge. However, in a large auditorium the time elapsed between the original sound and the reflection is much longer. In this case, the original sound and the echo reach your ear at different times, causing a confused sound, or a reverberation. If we make the original sound louder and reduce the reverberations, we can improve the acoustics of a room. Acoustics is the study of sound. We can reduce reverberations by cov­ ering the ceilings and walls with soundproofing acoustical tiles which absorb sound waves. Drapes and rugs are good sound absorbers.

Musical Sounds. Another characteristic of sound is quality. The quality of a sound de­ pends upon the number and type of overtones of the instrument producing the sound. Over­ tones are all the higher tones produced in addition to the fundamental tone the tone of lowest pitch. Two instruments playing the same notes of the same pitch and loudness may be distinguished apart because they pos­ sess different quality. A musical sound results from regular vibra­ tions having a definite pitch or pattern of rhythm and melody. The waves are regular in frequency and produce a pleasant sensation to the ear. Noises result from irregular vibra­ tions causing confused or loud sounds which produce a harsh, unpleasant sensation. -

Stringed Instruments. The lesser vibrations set up in different parts of a string give the violin and other stringed instruments their rich tones. The thickness, length and tightness of a string determine its pitch. A thick string produces a lower tone because it vibrates more slowly than a thin string of equal length. The amount of pressure applied to the strings changes the tone of a violin or other stringed instrument. In the piano, the proper tones are produced by adjusting the tightness and lengths of the strings. Wind Instruments. In wind instruments a column of air is set in motion. In the cornet, piccolo and flute, an air column is vibrated when air is forced through small holes into an air chamber. The fingers control the pitch by shortening or lengthening the c()lumn of air in the barrel of the instrument. The clarinet, oboe and harmonica are reed instruments in which a thin reed is set in motion by the breath. The vibrating reed sets the air column inside the instrument in action. In the horn, a column of air is vibrated and sound waves are spread by the horn's flare. How We Hear Sounds. In order to receive sound we need : ( 1 ) a vibrating body, ( 2 ) a conducting medium, such as air or water, ( 3 ) the ear to receive these sounds, and ( 4 ) a brain to interpret the sounds. 93

The ear consists of three parts : ( 1 ) the outer ear, ( 2 ) the middle ear, and ( 3 ) the inner ear. The outer ear, shaped like a fun­ nel, catches the sound waves. The drum sepa­ rates the outer ear from the middle ear. The middle ear contains a bridge of three tiny bones : the hammer, anvil, and stirrup. The middle ear is filled with air which must be kept at the same pressure as that on the other side of the eardrum in order not to damage the drum. When sound waves travel through the outer ear to the eardrum, the eardrum is vibrated. The vibrations are then transmitted through the middle ear to the inner ear. In the inner ear is the cochlea, which is filled with a liquid. The liquid carries the sound vibrations to tiny nerve fibers which, in turn, transmit the vibra­ tions to the auditory nerves. These nerves carry the impulses to the brain, where they are interpreted as sound.

MIDDLE EAR WITH BONES

WOODEN BOX t��_���_� �_ lI�I� � ·�� =�� 7 L BOARD ____ _

Producing a longitudinal wave in a spring.

Procedure: 1. Screw the wooden box to the board and attach the spring as shown in the illustration. The wooden box is to act as a sounding board. Attach a piece of ribbon to a coil in the middle of the spring to help visualize the nature of the wave. 2. Pinch together 1 0 or 1 5 of the coils on the right hand side of the spring, as shown in the diagram, and release them immediately.

Observations: 1. In the space provided, make a diagram of how the wave looked as it passed back and forth along the spring.

2. What did you observe when the wave

reached the box? . . . . . . . . . . . . . . . . . . . . .

STACHIAN TUBE TO THROAT

The human ear.

SELF-DI SCOVERY ACTIVITY

Producing a Longitudinal Wave and Study­ ing its Characteristics. Materials: A weak spring such as a Slinky toy, a screen door spring or a window shade roller spring, a box of thin wood, a board four feet long and one foot wide, and a piece of ribbon. 94

Conclusions: 1. Describe the appearance of the longitudinal wave in the spring. . . . . . .

.

. . .

.

. .

.

2. Explain the reason for the sound heard

when the wave struck the sounding box . . . .

REVIEW TESTS Completion Q uestions For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement.

1. In order to produce sound an object must . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Why is it not possible for sound waves to reach the moon? . . . . .

;

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.

..

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..

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.

3. A sound wave is characterized by alternate . . . . . . . . . . . . . . and . . . . . . . . . . . . . . of molecules. 4. At normal room temperatures sound travels at a speed of about . . . . . . . . . . . . . . . . . . . . . . . . .

.

5. What would be the velocity of sound in air at a temperature of 50° C? . . . . . . . . . . . . . . . . . . . . . . .

.

6. Sound waves are longitudinal waves since the molecules vibrate . . . . . . . . . . . . . . . . . to the direc­ tion in which the sound wave is moving.

7. What is sonar and how is it used? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8. Waves produced in water were seen to be 3 0 feet long and 20 of them p as sed

.

a specific point in

one minute. What was the velocity of these waves? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

9. What is the vibrating medium in a tuba? 10. As the frequency of a wave increases, the . . . . . . . . . . . . . . . . . . decreases. 11. What is meant by the term "frequency?"

12. What are ultrasonic vibrations?

.

.

13. The distance from the crest of one wave to the crest of another is called its . . . . . . . . . . . . . . .

.

14.

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. .

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Sounds with a high frequency are said to have a high . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

15. Echoes are caused by the . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . from a . . . . . . . . . . . . . . . . .

NAME

_____ _____

CLASS

DATE,

_ _ _.....

_ _ _ _ _ _ _ _

.

.

95

Multiple-Choice Questions In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question.

1. Sound will travel best through ( a ) air, ( b ) water,

2. As the amplitude of a sound wave increases the ( c ) loudness decreases, ( d ) loudness increases .

( c ) metal,

(d) acoustical tile.

(a) pitch decreases, ( b ) pitch increases,

3. The maximum number of vibrations that can be heard by most people is about (a) 20,000 vibrations/sec., ( b ) 50,000 vibrations/sec. , (c) 1 6 vibrations/sec., ( d ) 1 6,000 vibrations/sec.

4. Which of the following is not an important characteristic of sound? (a) frequency, ( b ) direc­ tion, ( c ) wave length, ( d ) amplitude.

S. As the temperature increases, the speed of sound (a) increases, ( b ) increases at first and then decreases, ( c ) decreases, ( d ) decreases at first and then increases.

6. At normal room temperature, sound travels at a rate of (a) 1 000 fL/sec., ( b ) 1 1 30 ft./sec., (c) 1 1 0, 000 ft./sec., ( d ) 1 00 m.p.h. 7. The loudness of a sound depends mainly upon its (d) wave length.

(a) pitch, (b) velocity, (c) amplitude,

S. Reverberation is (a) musical sound, ( b ) ultrasonic sound, ( c ) confused sound, (d) overtone.

9. The loudness of a sound is measured in

( a ) machs, ( b ) decibels, (c) v.p.s., (d) ft./sec.

10. At 0 0 C. sound travels in air at the rate of (a) 1 1 90, ( b ) 1 1 ,900, ( c ) 1 090, Cd) 1 0,900 ft./sec.

Match ing Questions In the space at the left of each item in Column A, place the letter of the term or expression in Column B that is most closely related to that item.

Column

Column A 1.

Mach

1

2. Auditory nerves 3. Wave length 4. Acoustics S. Rarefactions and compressions

6. Decibels 7. Echo S. Sonar 9. Vacuum

10. 1 1 1 0 feet/sec .

96

NAME

Q.

B

Carry electrical impulses to brain

b. Speed of sound at room temperature c. No sound transmitted

d. Distance from a point on one wave to the corresponding point on the next wave e. Caused by the reflectiQn of sound f. Study of sound g. Used to map the ocean floor h. Composition of sound waves i. Unit used to measure loudness of sound j. Speed of sound k. Speed of sound in air at l O °e. I. Longitudinal wave m. Column of air n. Sonic barrier o. 1 6 vibrations/sec.

_______

CLASS

DATE,

__

_ _ _ _ _ _ _

Chapter

11

LIGHT Can you imagine our world without light? Not only would there be constant blackness, but there would also be no life on our earth ! Without light, plants would not get the energy needed for growth. Without plants where would we get food? Furthermore, our planet would be a frozen mass. However, we on earth do have light, so let us learn more about the nature of this mysterious form of energy.

The Nature of Light. Light is a form of energy known as radiant energy. Light travels out­ ward in straight lines in all directions from a source. In space, light travels as very short transverse waves. ( The Latin prefix trans means "across. " ) In a transverse wave the particles of energy being transmitted vibrate at right angles to the direction of the wave motion.

Jle\ I Jle��DlRARTICFT'"ION "- i =� et DIRECTION OF � B

�

..

---­

Transverse wave.

Because light waves are made up of electric and magnetic energy, they are called electro­ magnetic waves.

Velocity of Light. Light travels through space at the speed of 1 8 6,000 miles per second. At this enormous speed, light from our sun ­ which is about 93 million miles away ­ reaches our earth in approximately 8 113 min­ utes. Because of the large distances involved, astronomical distances are often measured in light years. A light year is the distance that light travels in one year - about 6 trillion miles. Alpha Centauri, the nearest star to earth other than our sun, is about 4Vz light years away.

Theories of Light. The exact nature of light is still unknown. Sir Isaac Newton believed that light was a stream of tiny particles or corpuscles emitted by a source in all direc­ tions. A Dutch scientist named Christian Huygens believed that light was a series of waves. In the 1 9th century, James Maxwell, a Scottish physicist, proposed the idea that light waves are electromagnetic. Today, most scientists hold to the quantum theory of light developed by Max Planck, a German physicist, and confirmed by Albert Einstein. This theory states that light is trans­ mitted as electromagnetic waves consisting of tiny bundles of energy. Each bundle is called a photon or quantum. The greater the fre­ quency ( number of vibrations/unit time ) of the body emitting light, the greater will be the energy of the photon. In the chapter on atomic structure, you learned that electrons whirl around the posi­ tive nucleus in various orbits or energy levels. The energy level occupied by an electron is dependent upon its energy. The greater the energy of the electron, the farther it can move from the attracting force of the positively charged nucleus. When energy is added to an atom by heat­ ing, for example, the atom becomes "excited" and some of its electrons absorb enough energy to jump to a higher energy level farther away from the nucleus. This higher energy level represents a greater source of potential energy in the electrons. When no further energy is added, the electrons in the outer orbits return to their lower energy levels and some of their potential energy is converted to kinetic energy in the form of light. Large amounts of energy are needed to make electrons very close to the nu­ cleus jump to very high energy levels. When these electrons return to their lower energy lev­ els, they emit very penetrating radiation in the 97

fonn of X-rays. These rays possess a much higher frequency and a much shorter wave length than the light given off by electrons which jump through levels of relatively low energy. k--

�

WAVE 1

k

�

sec.

�

Long wave length. Low frequency.

LWAVEENGT AMPLlTUD�E l '1j

I

AM

�

1

sec.

�

Short wave length. High frequency.

As with a sound wave, the velocity of an electromagnetic wave can be found by multi­ plying its frequency (I) times its wave length ( l or A) . v

=

f X I or V

=

fX A

Since the velocity of electromagnetic waves is fairly constant in a particular medium, an increase in frequency results in a decrease in wavelength rather than an increase in velocity. Electromagnetic radiations with high fre-

quency have great penetrating power. Under certain conditions, excitation or disturbance of the nucleus may cause it to emit extremely penetrating gamma ('Y) rays.

Properties of Electromagnetic Radiations 1 . Possess both electrical and magnetic energy. 2. Travel through a vacuum at the speed of light - 1 8 6,000 miles per second. 3. Can transfer energy through a vacuum. Sunlight, for example, reaches us through the comparative vacuum of space. Radar waves have been bounced off the moon pennitting scientists to map its surface. 4. The energy transmitted by electromag­ netic radiation may be converted to other forms of energy only after it is absorbed by matter. Space, for example, is cold because there is very little matter to absorb the radiant energy of sunlight. Our earth and the matter on it are heated only after the radiant energy of the sun causes an increase in the speed of the molecules of the matter. The Electromagnetic Spectrum. Visible light is just one of the many kinds of electromag-

RELEASE OF ENERGY GAMMA RAYS X·RAYS

ABSORPTION OF ENERGY HIGH ENERGY LEVEL

-----

LOW ENERGY LEVEL o •

98

_ _ _ _ _ _

.....J

The a tom.

(PHOTON)

Electrons absorbing energy and jumping to a higher energy level. Electrons releasing electromagnetic radiation as they retUrn to a lower level.

Electrons in the outer orbits emit photons (light) when they return to a lower energy level. Electrons in the inner orbits emit X-rays as they return to a lower energy level. A disturbed nucleus will emit energy in the form of gamma rays.

THE ELECTROMAGNETIC SPECTRUM

Alternating Currents

Radio Waves

Infra-red ( heat) Waves

Visible Light

Ultraviolet Waves

X-rays

Gamma Waves

Cosmic Waves

3 X 1 0-7A

Increasing frequency and penetrating power. Increasing wave length, decreasing penetrating power.

netic radiations. Alternating currents, radio waves, television, radar, infra-red ( heat ) waves, ultra-violet rays, X-rays, gamma rays and cosmic rays are other examples of electro­ magnetic waves. Together these radiations make up what is called the electromagnetic spectrum. The left side of the chart of the spectrum illusti·ates electromagnetic radiations which have comparatively long wave lengths and very low frequencies. The wave length of electromagnetic waves is often measured in units called angstroms (A), extremely small units ( 1 A = 1 0 - 8 cm.), or 1 / 1 00,000,000 cm. As we travel toward the right side of the spectrum chart, the frequency of the radia­ tions increases and the wave lengths decrease. As the frequency increases, the penetrating power of the radiation increases. Alternating currents and radio waves have comparatively long wave lengths and very low frequencies ; thus, they have very little penetrating power. Cosmic and gamma rays have very short wave lengths and very high frequencies. These rays are highly dangerous since they can easily penetrate the body and damage the tissues. Our atmosphere protects us to a large degree from cosmic radiation from outer space.

What Is Refraction? The speed of light de­ pends upon the medium through which it is traveling. If the speed of light )s less in one substance than in another, the first substance is said to be an optically denser medium. When a light ray enters a medium having a different optical density at an oblique angle the light ray bends. This bending of light,

known as refraction, results from the differ­ ence in the speed of light in media of different optical densities.

LIGHT WAVE ENTERING

n

�

LIGHT WAVE

""- LEAVING . � �

GLASS PRISM

Refraction.

Dispersion of White Light. Sunlight consists of many different electromagnetic waves, each having its own wave length and frequency. By passing sunlight or white light through a denser substance such as a glass prism or water droplets, refraction OCcurs causing these different waves to be separated from the light. The different radiations are spread apart ( dis­ persed) into a spectrum of essentially six different colors - red, orange, yellow, green, blue and violet. Red light has the longest wave length and is least refracted. Violet has the shortest wave length and is refracted most. REFRACTIO N

LONGEST WAVE LENGTH

� . _� ?-t,=====

RED

ORANGE

� � YELLOW

P

E C

\",LET : GREEN

BLUE

DISPERS ION

S

T

SHORTEST WAVE LENGTH

Refraction and dispersion of s unlight.

99

SELF-DISCOVERY ACTIVITY

Observations: 1. List the colors seen in the spectrum in

Producing a Spectrum.

1. Investigating How a Glass Prism May

their proper order from left to right. . . . . . .

Be Used to Refract and Disperse White Light to Form a Spectrum. 2. Investigating How Color Is a Result of the Absorption, Reflection or Transmission of Light Rays.

ible in the spectrum when the red filter was inserted in the beam of light?

Materials: Triangular prism, slide projector, 2" X 2" opaque transparency or stiff paper cut from a 3" X 5" card, a red photographic filter or a few sheets of red cellophane.

Procedure:

2. What predominant color remained vis­

[�

1. Cut a narrow slit in the 2" X 2" opaque transparency or stiff paper as � seen at the right and insert it �. into the slide holder of the projector. 2. Arrange the equipment as seen in the illustration below. A movie screen or a stiff white paper ( about 2' X 2') may be used upon which to project the spectrum.

Conclusions: 1. What is the nature of white light? . . .

.

2. Explain how the spectrum was formed.

3. Which light ray was refracted least and which most? Explain why . . . . . . . . . . . . . .

3. Careful placement and rotation of the prism will produce a spectrum which will appear on the screen. The prism may be rotated to project the spectrum in the opposite direction if desired. 4. Note the colors found in the spectrum in their respective order from left to right. S. Place the red filter or red cellophane in the light beam between the projector and the screen and note the predominant color which remains. 1 00

.

4. Explain the reason for the predominant

color seen after the red filter was placed in the light beam between the projector and the spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

of producing a green color. The light is trans­ mitted to the retina of the eye and then to the brain where the actual interpretation of color takes place.

5. The color of opaque objects is caused

by the color they . . . . . . . . . . . and the color of transparent objects is caused by the color they 6. What colors are absorbed by a white

object? . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

Color of an Object. The color of an object de­ pends upon the wavelengths of light that the object absorbs, transmits, or reflects. White objects reflect all wavelengths of light. Black objects absorb all wavelengths, so none are reflected. This is why black is frequently called "the absence of color." Why does a green object appear green? . . . . . . . . . . . . . . . . . . . . .

Transparent objects, such as glass, air and water, transmit light readily, allowing objects to be seen easily through them. Translucent objects also readily allow light to penetrate them, but in so doing, greatly scatter the light, making seeing objects through them difficult An oil spot on a piece of paper and frosted light bulbs are examples of trans­ lucent objects. Opaque objects prevent trans­ mission of nearly all light rays. As light passes through an object, certain wave lengths will be absorbed. The color of the object, except black, depends upon the wave lengths which are transmitted. A green object, for example, appears green because it absorbs all wave lengths except those capable

Reflection. Objects are visible to us because of the light they transmit to our eyes. Lumi­ nous objects are those which emit their own light. A burning match, a light bulb, our sun and other stars are luminous objects. Illumi­ nated objects are those which are visible because of the light they reflect. The moon is an illuminated object because it shines by reflected sunlight. Objects seen in the beam of a flash­ light or a light bulb are illuminated objects. Light reflection refers to the rebounding of light rays off an object. The ray of light that strikes an object is called the incident ray. The ray that rebounds from a surface is the reflected ray. The line drawn perpendicular to the surface at the point where the incident ray strikes is called the normal. When light is reflected, the angle of re­ flection is equal to the angle of incidence. The angle of incidence is the angle between the normal and the incident ray. The angle between the normal and the reflected ray is the angle of reflection. This means that a light ray striking an object forming an angle of incidence of 45 0 will have an angle of reflec­ tion of 4 5 0 • If the surface is rough, the reflected light rays will scatter and produce what is called diffused light. Since very few surfaces are smooth, most reflected light reach­ ing us is diffuse in nature.

REFL EC TE O

Reflection from a smooth object a mirror. -

RA Y

Diffused reflection from a rough object.

1 01

Refraction. Light travels in straight lines in a particular medium and these straight lines can be bent or refracted when they pass obliquely through transparent substances hav­ ing different densities . As light passes through a more dense substance its velocity is reduced. The greater the density, the greater is the re­ duction in velocity. The ratio of the velocity of light in air or a vacuum to the velocity of an­ other substance is called the index of refraction. Index

of

Velocity of light

in air

Refraction = Velocity of light in another substance

Water has an index of refraction of about 1 . 3 , meaning that light travels 1 . 3 times faster in air than in water. The sparkle of a diamond is mainly caused by its extremely high index of refraction, which is 2.42. Various substances can be identified by determining their index of refraction. A ray of light entering an optically denser substance will be refracted or bent toward the normal . Conversely, light passing into a less optically dense substance will be refracted away from the normal. Light waves entering a second medium perpendicular to the surface will not be refracted.

Convex Lenses. A lens is a piece of glass or any other transparent material with two curved surfaces, or with one curved and one fiat surface. A convex lens is a lens which is thicker in the middle than at its edges. Re­ fraction through such a lens causes parallel light rays to converge (meet) at a point called the principal focus. The lens of your eye is a double convex lens that focuses an image on the retina of the eye. If a person is farsighted, his eyeball is too short from front to back, and the point of focus will fall behind the retina. Such people can see only distant objects clearly. Glasses with convex lenses are used to correct far­ sightedness. A magnifying glass is a double convex lens which behaves like two prisms connected to­ gether at their bases. It can concentrate light rays to such a degree that they can burn a hole in paper or cause a fire.

S

U N L

I G H

T AIR GLASS �,--t� I : - - - -NORMAL NORMAL- -�: RAYS -+-----� NO(TOPERRESURFPENDIFRACTIACCEUL)OANR V AIR

---->''"-

-+_�___�

__

PAPER

Convex

�

LIGHT

� I

: I

1-

- - -

Refraction in a prism. A magnifying glass converges and concentrates ligh t rays in a manner similar to prisms.

Refractions through different densities.

Refraction of light rays as they pass through water causes what appears to be a bending of a stick or pencil placed in the water. The difference between the actual location of the sun and its apparent location is caused by the refraction of light rays as they pass through our atmosphere.

1 02

Concave Lenses. A concave lens is thinner in the middle than at its edges and causes light rays to diverge ( spread apart) . If a person's eyeball is too long from front to back, the point of focus will be in front of the retina and the person will be nearsighted. He can see only close objects clearly. Concave lenses are used to correct nearsightedness.

D�E:S-W --Q -��T� � OF FOCUS F

Normal eye.

Farsighted.

-

Nearsighted.

Corrective lens ­

Corrective lens ­

convex.

concave.

Strength of a Source of Light. It is often important to determine the brightness of vari­ ous light sources. Homes, highways and busi­ ness enterprises must be well lighted. Optical instruments such as the camera and micro­ scope depend upon light for their operation. Photometry is the science of measuring light. A unit called a candle power is used to meas­ ure the rate at which light is emitted. In order to measure light a standard of comparison must be used. Originally, a specific type of candle called a standard candle was used for this purpose. One candle power ( CP ) is the rate at which this standard candle ( at present a standard lamp ) emits light under specific conditions. About 1 5 to 30 candle power of light is needed for reading. Bright sunlight emits about 1 0,000 candle power of light. The candle power of incandescent light bulbs is approximately equal to their wattage. A 60watt bulb, for example, is rated at about 50 candle power. Fluorescent bulbs are more efficient and emit more light per watt. A 20-watt fluorescent light produces about 50 c andle power of light.

in either ( 1 ) foot-candles ( ft. -candles ) or ( 2 ) lumens. A foot-candle is the intensity ( quantity) of light received by a surface placed one foot away from a source of light of one candle power. One candle power is equal to approximately 1 2 . 5 lumens. An instrument called a spherical pho­ tometer is used to measure the light intensity of various light sources. This device contains a photocell which converts light into electricity. Photocells called light meters or exposure meters are used in photography to measure the intensity of available light. They are also used to determine the amount of light needed for various other purposes. Scientists h ave discovered that the intensity of light varies directly as the candle power of the source and inversely as the square of the distance from the source. This is expressed mathematically by the foll owing formula : Foot-candles

=

Candle power of source

( Distance from source in ft. ) 2

If the candle power of the light source is doubled, the intensity of the light emitted will be doubled. If the distance from the source of light is doubled, the light will cover four times the original area but its intensity will be reduced to one-fourth. S ELF-DI SCOVERY ACTIVITY I nvestigating the Law of Illumination.

Materials: A strong light bulb ( about 1 00 watt) i n a lamp without a shade, a large piece of card­ board, large projection screen, a ruler or yard­ stick, and a room that can be darkened.

PIECE OF CARDBOARD

Intensity of Illumination. The intensity of light is the amqunt of light received by a surface at a certain distance from the source of illumination. Light intensity is measured 1 03

Procedure: 1. Cut a six-inch square hole in the card­ board, and arrange the materials as shown below. 2. Darken the room enough so that the light from the bulb illuminates the screen. Position the screen one foot away from the lighted bulb. Adjust the piece of cardboard so that light goes through the hole and illuminates a patch one­ foot square upon the screen. Observations: 1. Assume that a l OO-watt bulb produces 1 00 foot candles of illumination. What is the intensity of light in the one-foot square? . . . . 2. Move the screen two feet from the bulb.

What is the size of the square of light? . . . . . . .

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3. Since the light must spread out to cover this square, how much has the intensity of light decreased? . . . . . . . . . . . . . . . . . . . . . . . . . . .

4. Move the screen three feet from the bulb. Now what is the size of the square of light? s. How much has the light intensity de-

creased from the first location? . . . . . . . . . . . .

Conclusion:

The focal length is the distance from the lens to the principal focus, the point where parallel rays converge. The ordinary light microscope is used to investigate tiny structures such as cells and bacteria that would be otherwise invisible to the unaided eye. This instrument uses a com­ bination of convex lenses to obtain a maximum magnification of about 2000 times. An elec­ tron microscope using a beam of electrons can magnify objects as much as 500,000 times. This microscope has no lenses and magnetic fields are used to direct the beam of electrons. Viruses, which are disease-pro­ ducing structures so small they cannot be seen with an ordinary optical microscope, can be photographed with the electron microscope. The telescope also uses convex lenses to bring distant objects into view. Astronomical telescopes used to investigate the heavens are of two types : ( 1 ) the refracting telescope which uses two convex lenses, and ( 2 ) the reflecting telescope which uses mirrors to collect and direct light rays to a single lens. Today, radio telescopes collect radio waves from outer space. These telescopes have no lenses and are like huge radio or television antennas. The spectroscope is used to determine the elements present in a luminous object or gas. This is done by examining the spectrum pro­ duced when the emitted light is passed through a prism. Each element has its own characteris­ tic location and color in the spectrum. With the spectroscope, light coming from our sun and other stars has been investigated to deter­ mine the elements present.

in terms of your investigations? . . . . . . . . . . .

Eye glasses, cameras, projectors, binoculars and magnifying glasses are other optical in­ struments.

Optical Instruments. Optical instruments de­ pend upon lenses of certain focal lengths and adequate light sources for their operation.

Polarized Light. Some optical instruments use lenses which polarize light. Polarized light is light which vibrates in one plane rather than in all directions . Some useful applications of polarized light include the reduction of glare as in polarized sunglasses, and the identifi­ cation of certain crystals and chemicals.

Can you now state the Law of Illumination

1 04

R EVIEW TESTS Completion Q uestions For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement.

1. All electromagnetic radiations travel as a ( an ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . wave. 2. What are the characteristics and source of cosmic waves? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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objects allow light to pass through them but scatter the light, making the

viewing of objects through them difficult.

4. The moon is an example of a ( an )

object since it shines by reflected sun-

light.

5. Christian Huygens believed that all light was a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. What is a light year?

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7. What is meant by the "quantum theory?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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8. What scientist first proposed the quantum theory? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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9. As the frequency of a wave increases the . . . . . . . . . . . . . . . . . . . . decreases. 10. Why is space extremely cold, despite the fact that it is closer to the sun? . . . . . . . . . . . . . . . . .

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11. What type of electromagnetic wave has been bounced off the surface of the moon to map its surface? NAME

_______

CLASS

.DATE

��_

_ _ _ _ _ _ _ _

1 05

12. N arne the three types of electromagnetic radiations that possess the greatest penetrating power and .

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13. What helps to protect us from dangerous radiation from outer space? . . . . . . . . . . . . . . . . . . . . .

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highest frequencies

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14. Objects which prevent the transmission of nearly all light rays are called . . . . . . . . . . . . . . objects.

15. Why does an object appear black in color? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

16. The star nearest to our earth other than the sun is . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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17. What happens to light when it is reflected from a surface? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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18. Why is most light that reaches our eyes diffuse in nature? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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19. What is a practical application of determining the index of refraction of different objects? . . . . .

20. A light ray entering obliquely an optically denser substance from the air such as a glass prism would be refracted . . . . . . . . . . . . . . . . the normal. .

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lens is thicker in the middle than at the edges and is used to concentrate light

rays.

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is the science of measuring light.

23. Light intensity is measured in units called . . . . . . . . . . . . . . . . . . . . or . . . . . . . . . . . . . . . . . . .

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24. Why are fluorescent bulbs more efficient than incandescent bulbs? . . . . . . . . . . . . . . . . . . . . . . .

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25. What are light meters or exposure meters and for what purposes are they used? . . . . . . . . . . . .

26. If a bulb having a candle power of 1 50 were placed 5 feet from a screen, the intensity of the light reaching the screen would be 1 06

NAME

_ _ _ _ _ _ _� _______

CLASS

___

DATE

_____

27. What is meant by the focal length of a lens? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

28. Viruses can be seen only with the help of a ( an ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29. A reflecting telescope uses . . . . . . . . . . . . . . to collect and direct light to

an

eyepiece.

36-. What is a spectroscope and how is it used? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

31. What is polarized light and what are some of its uses? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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32. The shortest known wave is the . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . wave. 33. The bundle of energy in a light wave is called a ( an) . . . . . . . . . . . . . . . . or . . . . . . . . . . . . . . .

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34. Refraction of light rays as they pass through a jar of water in which a pencil is standing makes the

pencil look

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35. If the candle power of the light source is doubled, the intensity of the emitted light will be

Multiple-Choice Q uestions

In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question. 1.

Sunlight reaches the earth from the sun in abo ut (a) 763 seconds, ( b ) 8 minutes, (e) 1 3 minutes, (d) 1 hour.

2. Light energy may be emitted when (a) protons leave the nucleus, ( b ) the nucleus is disturbed, ( e ) electrons jump to higher energy levels, (d) electrons return to lower energy levels. 3. An infra-red wave is a(an) ( a ) light wave, ( b ) heat wave, (e) X-ray, (d) cosmic wave.

4. The wave length of electromagnetic waves is usually measured in units called (a) angstroms, ( b ) inches, (e) feet, (d) miles.

5. Many people are nearsighted. This condition can be corrected by (a) convex lenses, ( b ) concave lenses, (e) removing the lens of the eye, (d) eye exercises. NAM E�������

__ � � � _ _ _ _

CLASL

DATE �������_

__

1 07

6. The change in the direction of a light ray as it passes obliquely from a medium of one optical density to another is called (a) reflection, ( b ) rarefaction, (c) refraction, (d) resultant. 7. Which of the following colors has the longest wave length? (d) violet. S. Electrons in the outer orbits of an atom emit (d) angstroms.

(a) red,

( a ) protons,

( b ) green, ( c ) blue,

( b ) neutrons,

(c) photons,

9. Radio waves have (a) long wave lengths and high frequencies, ( b ) short wave lengths and low frequencies, ( c ) long wave lengths and low frequencies, (d) short wave lengths and high fre­ quencies. 10. Luminous objects are (a) transparent, (d) visible only in reflected light.

( b ) able to emit their own light,

(c) translucent,

Matching Questions

In the space to the left of each item in Column A, place the letter of the term or expression in Column B that is most closely related to that item. Column

Column A ·

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..

1. Particles move perpendicular to the direction of the wave

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2. Proposed the electromagnetic nature of light rays

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... ...

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3. Ratio of the velocity of light in air to the velocity of light in another substance

4. Unit used to measure light intensity

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5 . Velocity of light in a vacuum

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6. Shortest wave length in light and is refracted most

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7. Absorbs all wave lengths and transmits none

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8. Prevent transmission of light rays

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9 . Causes light rays to diverge 10 . Emit their own light

NAME

______

CLASS

A..- ATE D

_ _ _

B

a. Isaac Newton b . Luminous objects c. Violet d. James Maxwell e. Longitudinal wave f . Black g. Convex lens h. Refractive index i. Transverse wave j. Foot candle k. 1 8 6,000 mi./sec. I. Concave lens m. Opaque objects n. Frequency o. 1 1 00 ft./sec.

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Chapter 1 2

H EAT

SOU RCES OF H EAT EN ERGY

Everyone has at some time stood before a fire and felt its heat. You've often lain in the sun and been warmed by its heat. One of early man's greatest discoveries was fire; it provided him with the heat necessary for cooking, for warmth and for protection from animals. What is heat? Where does it come from? Heat is a form of energy. All forms of energy can be transformed into heat. The earth gets more than 9 9% of its heat in the form of radiant energy of the sun. Scientists think that this radiant energy results from the nuclear reactions taking place on the sun. Without this source of heat there would be no life on earth. Much of the heat that we use every day comes from chemical energy. Most chemical reactions give off heat. Much of our body heat comes from the oxidation of digested foods, a chemical process. Burning fuels heat our homes and buildings, cook our food and provide the driving force for various types of heat engines which convert heat into mechanical energy.

Electrical energy may be converted to heat energy which is used to heat homes and buildings and to cook our foods. We iron our clothes and solder metals with heat obtained from electricity. Heat is also obtained from mechanical energy. Friction always produces heat. This is often unwanted heat which reduces the efficiency of a machine and wears out its parts. The mechanical compression ( squeezing ) of molecules produces heat. This heat is used, for example to produce the combustion of fuel in huge diesel engines . Tremendous forces of compression on the upper layers of the earth are believed to be responsible for the immense pressure and heat found in the interior of the earth.

Nuclear energy produces vast amounts of various kinds of energy, including heat. To­ day, man is tapping this source of heat and using it to change water into steam. The steam is used to drive turbines which run generators or to propel ships and submarines. Much of man's future energy needs will be supplied by energy from nuclear reactions. H EAT AND TEMPERATU RE

Heat is a form of energy which may be absorbed, emitted or transferred between ob­ jects of different temperatures. Matter is composed of molecules which are always in a state of motion. All matter pos­ sesses some quantity of heat. The quantity of heat present in a mass is dependent upon the number, mass and the total kinetic energy of its molecules. Temperature is a measure of the intensity of heat or cold. Temperature is dependent upon the average kinetic energy of the mole­ cules of a mass. Heat energy will produce a measureable change in temperature when enough energy is absorbed by enough mole­ cules (matter ) to cause a significant increase in the average kinetic energy of the molecules. Why is space so very cold? Because there is very little matter to absorb energy and convert it to heat. Two identical substances may have the same temperature but may possess different quantities of heat. A glass of water and a lake, for example, may have the same tem­ perature, but the lake contains much more heat because it has so many more molecules in motion. Two different substances of the same weight may be heated with the same intensity, yet may have different temperatures. Work must be done to cause the molecules of the mass to move. Different substances require different 1 09

amounts of energy to perform the work of increasing the velocity of their molecules. Heat, under some conditions, may be added or removed from a substance without chang­ ing the temperature of the substance. Such a phenomenon occurs when the physical state of matter is changed to a solid, liquid or gas . In changing ice to water, for example, the energy is used to overcome molecular attrac­ tion, rather than increasing the total kinetic energy of the molecules.

Measuring Temperature. Temperature is ex­ pressed in degrees and is measured with vari­ ous kinds of thermometers . In most scientific work and in most countries, the Celsius or Centigrade scale is used to express tempera­ ture. The boiling point of pure water on this scale is 1 00 ° e. and the freezing point of pure water is 0° C. The Fahrenheit scale is still commonly used in the United States and a few other countries. On this scale, the boiling point of pure water is 2 1 2 ° F., and the freezing point is 3 2 ° F. The following formulas are used to convert from one scale to the other : OF. ° C.

= _

t e . o + 3 2 or e.

- 9 5

(F. ° - 3 2 ) or

0

X 1 .8 + 32

F.o - 32 1 .8

For example, 20 ° e. is equal to 68 ° F. OF.

=

t e . 0 + 32

OF.

=

OF.

=

36 + 32

OF .

=

68°

;

(20) + 32

A third scale, the Kelvin scale, has the lowest possible temperature reading of - 45 9 . 69 ° F. or -27 3 . 1 6 ° C., which repre­ sents absolute zero. At this temperature molec­ ular energy theoretically disappears, and all gases are condensed. This is, theoretically, the coldest possible temperature. This temperature has never been reached but, experimentally, scientists have come very close to it. The study of extremely low temperatures, beginning be­ low - 1 50 ° F., is called cryogenics. 110

To convert a Centigrade reading to a Kelvin temperature, simply add 273 ° to the Centi­ grade reading. OK .

=

e. 0 + 273

SOME IMPORTANT TEM PERATURES

Boiling point of pure water

FO

CO

KO

212

1 00

373

Normal average body temperature

98.6

37

3 10

Room temperature

68

20

293

Freezing point of pure water

32

0

273

Absolute zero

-459.69

-273 . 1 6

0

Measuring Heat. In the metric system, heat is measured in units called small calories or large Calories. A small calorie (used in most laboratories ) is the amount of heat needed to raise one gram of water 1 0 C. The large Calorie is used to measure the energy value of foods. It is equal to 1 000 small calories and is the quantity of heat necessary to raise the temperature of 1 000 grams of water 1 ° e. A calorimeter is used to determine the number of calories of heat present in foods and other materials. In the English system, heat is measured in British thermal units (B.T.V.). One B .T.U. is the amount of heat necessary to raise the temperature of one pound of water 1 ° F. One B . T.U. is equal to 252 calories. The heat energy of fuels is usually expressed in B.T.U.s. H EAT TRANSFER

Heat is transferred between objects of dif­ ferent temperatures until an equilibrium point is reached when both objects have the same temperature. Heat energy always travels from a hotter object (higher temperature) to a

colder object (lower temperature ) . An ice cube placed in a glass of water gradually melts because heat passes from the water to the ice cube, gradually increasing the kinetic energy of the molecules of the cube. The water, of course, cools during this process as its heat is gradually lost.

1. Conduction. Solids transfer heat by con­ duction. In this process, energy added to a solid increases molecular motion. The heat energy is transferred from one· molecule to the next, through molecular collisions, until all the molecules are moving more rapidly. This process of heat transfer will continue until every part of the solid has the same temperature ; that is, the same average molec­ ular motion. Heat is transmitted from one end of a metal rod to the opposite end by conduction. Heat resulting from friction is also transferred by conduction. Most metals, such as copper and aluminum, are good conductors of heat. Most non-metals, such as brick, wood, asbestos, rock wool insu­ lation, air and rubber are poor conductors of heat and are therefore used as heat insulators . 2. Convection. The chief method of heat transfer by liquids and gases is called con­ vection. As the fluid is heated, the portion being heated expands and becomes less dense. As the less dense portion rises, the surround­ ing colder, denser fluid sinks and moves into its place to become heated. As this process takes place, a convection current is set up which transfers the heat. The process will continue until the same temperature exists throughout the fluid. Hot air furnaces, boilers, hot water heaters, the heating of our atmosphere and oceans are all dependent upon the transfer of heat by convection.

3. Radiation. The transfer of heat energy through space by means of electromagnetic radiation ( waves ) is called radiation. Radiant energy, unlike the other two methods of heat transfer, travels at the speed of light 1 8 6,000 miles per second, and can pass

through a vacuum. This is very important, for it is by this method that energy given off by the sun reaches the earth. Some of the radiant energy that falls upon matter may be absorbed and converted to heat. Dark-colored objects are good absorbers and poor reflectors of heat energy. Black, rough surfaces heat quickly and radiate heat rapidly. White or light-colored objects and highly polished, smooth surfaces such as silvered objects or aluminum reflect heat.

�f 1iJi

SIl�WHIRE'TE OR

S OTH SURFACE � ••

�

, _ROUGHACE �URF

Radiation is reflected by light colors and absorbed by dark colors.

SELF-DI SCOVERY ACTIVITY Investigating Absorption and Radiation of Heat.

Materials: Two test tubes, a beaker, aluminum foil, black paper or cloth.

Procedure: 1. Fill two test tubes half full of water and cover one of them with aluminum foil and the other with black paper or cloth. 2. Insert a thermometer into each test tube and place the test tubes in a beaker. Allow the beaker to remain in a shady place until the temperature of the water in both tubes is the same. 3. Place the beaker in bright sunlight or near a 1 00-watt bulb or a heater. Record the temperatures of the water after 5 and 1 0 minutes in the chart on page 1 1 2. 111

SUNLIGHT �-+++-THERMOMETER fiJ/Y,Ot-;-A L U MI N UM FOI L ��-r--- BLACK COVERING BEAKER

Effects of Heat Energy

4. Replace the beaker in the shaded lo­ cation and record the temperatures of the water after 5 and 1 0 minutes.

Conclusions: 1. In which tube did the temperature In­

crease and decrease most rapidly? Why?

2. The aluminum foil . . . . . . . . . . . . . . . . much of the heat reaching the test tube.

Procedure

Time

1. Heat energy can be used to perform work. The study of the relationship between heat and work is called thermodynamics. 2. Heat energy can cause an increase in the temperature of an object. 3. Heat, in most cases, causes solids, liquids and gases to expand in volume due to the increased molecular energy and a greater distribution of their molecules. Contraction takes place when a substance loses heat and its molecules move closer together. Expansion joints in concrete roads and sidewalks, radiator overflow pipes, loops in pipes carrying steam, safety valves in boilers and soft plugs in automobile engine blocks are used to avoid damage due to expansion caused by overheat­ ing. Solids and liquids expand at different rates. The rate at which substances expand is also very important. Most thermometers are de­ pendent upon the fact that substances such as mercury or alcohol expand and contract uniformly with changes in temperature. Rapid expansion of ordinary glass may cause it to break if it is exposed to sudden, marked temperature changes. Pyrex or Corning ware, on the other hand, have very low rates of expansion and thus will not ordinarily break under the same conditions. Thermostats contain two strips of metals which have different rates of expansion. These strips are joined together to form a single, compound bar. When the thermostat bar straightens it touches a contact point in the

Temperature

Time

Beaker in hea t Test tube + aluminum foil

5

min.

10

min.

Test tube + black covering

5 min.

10

min.

Test tube + aluminum foil

5 min.

10

mill .

Test tube + black covering

5 min.

10

mill .

Beaker in shade

112

Tempera ture

thermostat and completes the electrical circuit. This may start your furnace, refrigerator or other device. When the metals expand and bend away from the contact, the electrical circuit is broken and the apparatus will shut off.

The thermostat.

MOTOR SOURCE OFTOCURRENT

Water is similar to other substances , since it expands when heated under most circum­ stances. It is unique; however, because it contracts and its density increases as its tem­ perature is raised from 0° C. to 40 C. The density increases because of the decrease in volume. Water has its maximum density of 1 g. jcm3 at 40 C. As the temperature is lowered from 40 C. to 0° C. it expands , be­ comes lighter, rises to the surface, and freezes as ice. The blanket of ice on the surface of a body of water provides insulation which pre­ vents all the water in a lake or pond from freezing and killing aquatic life. Dissolving certain substances in water usually lowers its freezing point and raises its boiling point. Antifreeze added to radiator water prevents freezing which could damage the radiator and engine of an automobile. Gases differ from solids and liquids with respect to expansion, in that all gases expand at approximately the same rate. 4. Heat or the loss of heat, may cause a change in the state of matter. An increase in heat may cause a solid to melt or a liquid to boil and evaporate, forming a gas. Some solids, such as iodine will form a vapor without first forming a liquid. The higher the temperature, the more rapidly the substance will melt, boil or evaporate, since its molecules will be absorb­ ing more energy and moving faster. When the molecules of a solid receive enough energy to

overcome the cohesive forces of attraction be­ tween molecules, primarily gravitational and electrical in nature, the solid melts , forming a liquid. As the liquid is further heated, the molec­ ular energy and motion increase and the liquid begins to boil. Some of the molecules receive enough energy to break away from the liquid and form a gas. This process is called vaporiza­ tion. These escaping molecules must have suffi­ cient energy to oppose the pressure of the air above them. When air pressure is reduced, the boiling point is lowered and substances . will vaporize more quickly. Rapid vaporization is is called boiling. Slow vaporization is called evaporation. A loss of heat causes a decrease in molec­ ular energy and motion. As the molecules slow down and draw closer together, cohesive forces increase. During this process gases will be­ come liquids. This process is called condensa­ tion. As the temperature decreases further, the liquid will become a solid and the molecules will vibrate in a fixed position, giving rigidity to the material. 5. Heat energy will cause certain chemical reactions to occur and usually cause chemical reactions to speed up. 6. Heat can produce electricity when two different metals are joined together and there is a temperature difference between the two junctions. A device, called a thennocouple, uses this technique to produce electricity.

SELF-D I SCOVERY ACTIVITY Using a Thermocouple to Produce Electricity.

Materials: Copper wire, coat hanger, candle, gas burner, beaker, icewater, sensitive galvanom­ eter. Procedure: 1. Connect the ends of two copper wires to a galvanometer and then twist the other two ends together. Heat the j unction ( twisted 1 13

ends ) in the flame of a Bunsen burner and record the results observed on the galvan­ ometer.

2. Sand off the paint from a piece of coat hanger wire. Make a junction of one end of

COPPER WIRE

the wire with an end of a piece of copper

I

Heat the junction of the wires in a

candle flame and record the galvanometer reading.

4. Apply a Bunsen burner flame to the

junction and record the galvanometer reading.

COPPER WIRE \

t

-+--BBURNEUNSENR

l:: "' GALVANOMETER

wire. Connect the free ends of the wires to the galvanometer.

3.

IRON WIRE

1. Explain the principle of the thermo-

JUNCTION �

couple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

-��-....--...

-

r TER GALVANOME

·"'--BUNSE BURNENR 2. How could you increase the amount of

S. Cut the copper wire and insert the

galvanometer.

Twist

the free

ends

of

electricity produced by a thermocouple? . . .

the

copper and iron wire together and place the junction in a beaker of ice water. Heat the other junction in the Bunsen burner flame, and record the galvanometer reading.

3.

Since the amount of electricity produced

varies with temperature, the measurement of the electric current produced could enable us

Observations: Record your observations in the following

to use the thermocouple as a . . . . . . . . . . . . . .

chart :

Procedure 1 . Two copper wires 3. Iron + copper wire and candle flame 4. Iron + copper wire and Bunsen burner flame 5.

Iron + copper wire . One junction in ice water, the other heated in a Bunsen burner flame

114

Galvano me ter Reading

REVIEW TESTS Completi on Questi ons

For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement. 1. Heat is a form of energy produced by the motion of . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.

A temperature of -459.69° F. represents zero in the . . . . . . . . . . . . . . . . scale.

3. What is temperature? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4. Heat is related to the . . . . . . . . . . . . kinetic energy of the molecules; temperature is related to the . . . . . . . . . . . . kinetic energy of the molecules. 5. Explain why two objects may have the same temperature but may differ in the amount of heat they contain.

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6. The . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . temperature scale is used for most scientific work and is commonly used in most countries of the world. 7. A thermometer showed a temperature of 1 5 ° C. This is equal to a temperature of . . . ° F. .

8. Air may be liquefied by compressing it and lowering its temperature to about - 200° C. This temperature is equal to a temperature of

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10. The heat energy of fuels is generally measured in units called . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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11. Define the term "small calorie." . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

12. Why would telephone wires snap in winter, if they were installed in a taut manner in summer?

NAME�����_�

_ _ _ _ _ _ _ _

CLASS'��-Lo'DATE

� _ _ _ _ _ _

1 15

13. The inside of a thermos bottle contains a bottle made of glass. Between the glass walls there is a partial vacuum. The inner and outer parts of the glass walls are coated with silver and the container is closed with a cork. Explain how these various details help to keep materials in the .

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15. What are convection currents? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

16. Radiation is the transmission of energy including heat, as a ( an ) . . . . . . . . . . . . . . . . . . . . wave. 17. Radiant energy produces a significant rise in temperature only after it is . . . . . . . . . . . . . . . . . . by sufficient matter. 18. Why do cooking utensils often have a copper bottom? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

19. Heat will continue to flow between objects until . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

20. Explain why storm windows and woolen clothing help to keep us warm. . . . . . . . . . . . . . . . . . . .

21. In what states of matter is heat transferred by convection? 22. As water is heated from 00 C. to 4 ° C. its volume will 23. Water has its maximum density at 116

NAME

° C. ---

-

-- --------

24. As me temperature of water decreases from 4° C. to 0 ° C. it becomes less dense and . . . . . . . . . . . . 25. What is unique about the expansion of all gases under normal conditions? . . . . . . . . . . . . . . . . .

26. If you placed two eggs in boiling water, while camping high in the mountains, why would you have to wait for a longer period of time to have them properly prepared? . . . . . . . . . . . . . . . . .

27. Heat energy usually causes a chemical reaction to . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2S. When dissimilar metals are joined together at both ends and a temperature difference exists between their junctions an . . . . . . . . . . . . . . . . . . . . . . . . . . . . . is produced. 29. Much of our body heat is a result of oxidation, which is a

process.

30. Pure water freezes at . . . . . . ° C. and . . . . . 0 F. .

Multiple-Choice Questions In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question.

1. Body heat comes mainly from (a) electrical energy produced by the cells, ( b ) the mechanical breakdown of foods, (c) oxidation of digested nutrients, (d) exercise. 2. Which of the following objects will most readily absorb heat? (a) highly polished aluminum foil, ( b ) a rough black surface, (c) a smooth black surface, (d) a rough white surface.

3. The main source of heat energy for the earth is (a) the sun, ( b ) chemical energy, (c) mechanical energy, (d) potential energy. 4. At absolute zero (a) objects are at their hottest possible temperature, ( b ) all molecular energy theoretically disappears, (c) molecular energy is at its minimum, (d) water freezes. 5. Which of the following can be converted to heat energy? radiation, (c) chemical energy, (d) all of these.

(a) electricity, ( b ) electromagnetic

6. As a solid melts, its temperature (a) increases, ( b ) decreases, (c) varies, (d) remains the same. same. 7. The study of the relationships between heat and work is called (a) cryogenics, ( b ) chemistry, ( c ) thermodynamics, (d) combustion. S. Heat energy of foods is measured in units called (d) Calories. NAME

_ ____� _

_ _ _ __ _ _ _ _ _ _

CLASS

(a) degrees,

___

DATE

( b ) B.T.U.s,

_ _ _ _ _ _

(c) ft.-lb.,

117

9. Heat produced by friction in solid objects is transferred by (a) conduction, ( b ) convection, (c) radi­ ation, (d) none of these.

10. The blower in a furnace may be controlled by (a) thermometer, ( b ) thermocouple, ( c ) thermo­ stat, ( d ) thermograph.

Matching Questions

In the space at the left of each item in Column A, place the letter of the term or expression in Column B that is most closely related to that item. Column B

Column A a.

1. Converts heat into mechanical energy

Vacuum b. Boiling c. Thermocouple d. Thermostat e. Diesel engine f · Dissolved substances g. Evaporation h. Friction i. 200 C. j. Iodine k. Silver I. Compression m. 3 7 ° C. n. Pyrex

2. Lowers the freezing point and raises the boiling point

3. Very low rate of expansion 4. Two dissimilar metals joined together and a difference in temperature exists at their junctions 5. Slow vaporization of a liquid 6. Forms a vapor without first entering the liquid state 7. Conducts only radiant heat

8. Often produces unwanted heat 9. A major cause of the internal heat of the earth

10. Normal average body temperature

118

NAME

_ _ _ _ _ _ _ _ _ _ _--

CLASS

DATE

___

_ _ _ _ _ _

Chapter

13

N UCLEAR E N E RGY

Today, nations of the earth are using more and more energy for production, building, and daily life. However, at the same time, the earth's reserves of coal and crude oil are rapidly dwindling. Where will future genera­ tions obtain energy when all such fuel is gone? Nuclear energy, or energy from the nucleus of the tiny atom, may be the answer. This vast source of energy was discovered and made available by a series of important contributions from scientists of many nations.

1. The Develop�ent of Nuclear Energy. In 1 8 95, Wilhelm Roentgen, a German physicist, discovered X-rays, which are similar to light waves but have a much shorter wave length and a much higher frequency. Wave length refers to the distance between the crest of one wave and the crest of the next wave. Frequency refers to the number of waves or vibrations in a given time interval. Henri BecquereJ of France was one of the early pioneers in the field of nuclear radiation. In 1 896, he saw a strange glow coming from a sample of uranium ore that had been placed in the dark. He discovered that the invisible rays which caused this strange glow, and which he called radiations, affected a photo­ graphic plate in much the same manner that ordinary light affected it. Although he did not realize the importance of his discovery, Becquerel was probably the first man to wit­ ness radioactivity, a phenomenon in which an unstable nucleus undergoes spontaneous dis­ integration and gives off radiation. In 1 8 98, Marie and Pierre Curie of France discovered that strange radiations were being given off by the radioactive elements radium and polonium, found in pitchblende, an ore of uranium. They concluded that it was the natural breakdown or decay of these radio­ active elements that caused the emission of these strange radiations.

In 1 903, Ernest Rutherford, an Englishman, discovered that radioactivity was visible proof that matter could be transformed into energy as a result of atomic disintegration. He further learned that the products of atomic disintegra­ tion consisted of particles and rays, now known to be alpha and beta particles and gamma rays. Rutherford, in 1 9 1 9, was also the first to bring about the transmutation of elements. Transmutation, as you have learned, is the changing of one element into another by changing the number of protons in the nucleus. A giant step forward was taken in 1 90 5 , when the great German-American physicist, Albert Einstein, developed the theory that matter and energy were actually different forms of the same thing. His equation, E = mc2 , indicated that a small amount of matter can be converted into a vast amount of energy. Atomic radiation is one of the forms of energy reSUlting from the actual destruction of tiny amounts of matter. In 1 932, the English scientist, James Chad­ wick, discovered the neutron. This was an important discovery, for this nuclear particle was later to be used as an atomic bullet to split the atom and release the energy locked in it. The process of splitting the nucleus of an atom is called fission or nuclear fission. In 1 93 8 , the German scientists, Otto Hahn and Fritz Strassmann were the first to split the atom. They split the uranium atom by firing a neutron into its nucleus. This resulted in the formation of two lighter atoms of krypton and barium, coupled with the release of a large amount of energy. Enrico Fermi, an Italian-American physi­ cist, and his associates, developed a method of harnessing the power of the atom. At the University of Chicago, in 1 942, they produced the first controlled chain reaction. A chain reaction is a nuclear reaction in which the 119

splitting of the atomic nuclei ( fission ) releases enough neutrons to make the reaction continue until all the fissionable material is used up. On July 1 6, 1 945, the first nuclear bomb, or "atomic" bomb, was exploded in the deserts of New Mexico. On August 6, 1 945, during World War II, a nuclear bomb was dropped on Hiroshima, Japan. The first practical applica­ tion of nuclear power was witnessed in 1 95 4 with the launching of the U.S. nuclear-powered submarine, the Nautilus. This submarine can travel for approximately one year, without re­ fueling, on 1 2 pounds of uranium fuel. The energy of the atom is used to change water into steam and the steam in turn drives the turbines. A turbine is an engine, powered by steam, water or gas, that is turned by means of a wheel fitted with curved vanes or blades. In 1 954, ground was broken at Shipping­ port, Pennsylvania, for the first large-scale nuclear power plant in the United States. In 1 95 6 , the world's first large-scale nuclear power plant, used for the production of elec­ tricity, was put into operation. This was the Calder Hall nuclear power plant in England. The first nuclear-powered merchant ship, the Savannah, was launched by the United States in 1 9 5 9.

alternative to our fast-dwindling supplies of non-renewable fuel resources, such as coal and oil. Countries that lack adequate water power for the production of electricity can turn to nuclear reactors as the solution to their energy problems. Nuclear energy tapped from re­ actors can be used to power desalting devices, which remove salt from sea water, and thus help to solve the serious world-wide water shortages. Radioisotopes, used in medicine and research, are usually made in an atomic pile. Nuclear engines are being developed to power airplanes, trains, space vehicles and other means of transportation. Today, the United States has dozens of nuclear-powered submarines and surface ships. Nuclear power has been used to provide electrical power for satellites and for remotely controlled experi­ mental stations on the moon. The nuclear reactor harnesses the energy obtained from a controlled chain reaction of fissionable material ( nuclear fuel) , such as uranium-23 5 . The nuclear fuel is inserted into the pile in aluminum tubes, called slugs. Enough U-23 5 is furnished to provide a critical mass, or the amount of nuclear fuel necessary to bring about a chain reaction. As the fission or splitting of the U-2 3 5 nuclei takes place, each atom of U-2 3 5 is changed into two smaller atoms, one of barium and one of krypton. In addition, a small portion of the mass of the U-23 5 atom

2. Nuclear Reactors. A nuclear reactor is a type of nuclear furnace, often called an atomic pile. These reactors can provide an

BORON OR CADMI U M CONTROL RODS CONCRE T E SHI E LDI N G ---, ( A BSORB E X CESS NE U TRONS) (PROTECTIVE) (GRAPHI SLOWSTDOWNE MODEFRREATORNEU:;'TRONS)iNs:i�iJllilllllll i!�����P;;;;�;;;�; WIALTUHMIURANINUM TUUMB�ES;F�IL�L�ED�= FUEL r-----

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A large nuclear reactor.

120

- often water or liquid sodium. This heated liquid in turn is used by a boiler to convert water into steam power. If the chain reaction were not controlled, a violent explosion, similar to that of a nuclear bomb, would take place. In order to keep the chain reaction under control, control rods, containing either the element boron or cadmium� are placed in the reactor to absorb free neutrons. As these con­ trol rods are inserted farther into the reactor, more neutrons are absorbed and the chain reaction can be slowed down or even stopped. As the control rods are pulled out of the pile, more neutrons are made available to increase the rate of the chain reaction and provide more energy. Synthetic elements have been created in nuclear reactors as well as in huge machines called particle accelerators, which tremen­ dously increase the speed of atomic par­ ticles. Some examples of these accelerators or atom smashers, as they are sometimes called, are the cyclotron, bevatron, megatron, synchrotron and betatron. Scientists are now perfecting special types of nuclear reactors called breeder reactors. These will be designed to produce more atomic fuel than they consume.

KRYPTON NUCLENEREGYAR

+

Fission of uranium-235.

is converted into an enormous amount of energy. During the fission process, neutrons are released which act as atomic bullets to split the nuclei of more U-23 5 atoms, bringing about a chain reaction. Since slow neutrons are more effective in bringing about such a chain reaction, a material called a moderator is used to slow down the fast neutrons that are freed in the original fission. The moderator usually consists of graphite ( carbon ) blocks which form the basic framework of the atomic pile. It may also consist of heavy water con­ taining deuterium. Since some of the energy radiated during the fission process is in the form of dangerous gamma rays, a protective shielding of concrete is provided as a safety precaution. A tremendous amount of heat energy is produced in the atomic pile. The reactor is kept cool by transferring the heat to a liquid

3. Nuclear Fusion. In nuclear fission, the nuclei of heavy atoms are split to produce energy. In nuclear fusion, on the other hand, the nuclei of light atoms are fused or united,

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under conditions of extreme heat, to form elements of greater atomic weight. Fusion reactions are accompanied by the release of fantastic quantities of energy which result from the conversion of tiny amounts of matter into energy according to Einstein's equation E = mc2• Because of the tremendously high temperatures necessary to bring about atomic fusion ( several million degrees ) , these re­ actions are often referred to as thennonuclear reactions. An example of a fusion reaction is the combining of the nuclei of four hydrogen atoms to form a single atom of helium. The nuclear bomb, or "atomic bomb," is based on a fission reaction, whereas the hydro­ gen or thermonuclear bomb is based on a fu­ sion reaction. The energy of the stars, including our own sun, is thought to be a result of the fusion of hydrogen atoms. 4. The Present and Future Uses of Nuclear Energy. Once the energy resulting from nuclear fission and fusion becomes economically com­ petitive with other forms of energy, mankind will reap untold benefits . This is, of course, providing he learns to live in peace with his fellow man. Nuclear energy is used in industry in the production of electricity. Submarines, cargo ships, and space vehicles are powered by nu­ clear energy as may be the trains, airplanes, and even motor vehicles of the future. Radio­ active elements or tagged atoms are used in tracer research ; they can be detected and fol­ lowed to investigate chemical reactions, and to detect flaws in metals. In medicine, radioactive iodine and cobalt

1 22

are used to treat cancer, radioactive phos­ phorus is used to locate tumors, and radioac­ tive iron is used to investigate circulation and the red blood cells. In agriculture, carbon- 1 4 is used to investi­ gate photosynthesis. Nuclear power is used to desalt sea water and increase the water supply. In genetics, X-rays and radioisotopes help in the study of the effects of radiation on the genes which control the traits we inherit. In geology, the rate of decay of uranium to lead is used to estimate the age of rocks, and the rate of decay of carbon- 1 4 can determine the age of certain fossils.

SELF-DISCOVERY ACTIVITY Observing Nuclear Fission.

Materials: A watch with a luminous dial and h ands that have been coated with paint that contains a tiny amount of radium or other radioactive material ; a strong magnifying glass or 1 5X stereo microscope. Procedure: In a darkened room, focus the m agriifying glass or the microscope on a glowing part of the watch dial. Observe carefully. What do you see happening? . . . . . . . . . . . . . . . . . . . . . . .

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Explain this in terms of nuclear fission :

R EVIEW TESTS Completion Questions For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement. 1. Although X-rays are similar to light rays in that they both possess electrical and magnetic properties, they differ from each other in that X-rays can penetrate the skin and . . . . . . . . . . . .

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is one of the ores from which uranium is obtained.

3. According to Albert Einstein, a small amount of matter can be changed into a vast quantity of •

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4. What is the meaning of the term "critical mass?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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5. The first man to bring about the transmutation of an element was . . . . . . . . . . . . . . . . . . . . . . . .

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6. What happens when the nucleus of a uranium-23 5 atom is split? . . . . . . . . . . . . . . . . . . . . . .

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in the deserts of . . . . . . . . . . . . . . . . . . . .

9. A turbine is used to turn a generator in the production of electricity by nuclear power. What is the driving force of this turbine and how does it originate? . . . . . . . . . . . . . . . . . . . . . . . . .

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10. A nuclear reactor is sometimes called an atomic furnace or an . . . . . . . . . . . . . . . . . . . . . . . . .

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12. Mankind first witnessed the practical application of nuclear energy in the year . . . . . . , with the launching of the nuclear-powered submarine named the . . . . . . . . . . . . . . . . . . . . . . . . . . . . . NAME

______

CLASS

D �ATE

__ __ __

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1 23

13. Complete the following chart which compares a fission and a fusion reaction, by filling in the blanks with the correct answers. Fu sion

Fi ssion Atomic weight of nuclear fuel (light, heavy )

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Effect on nuclei Atomic weight of resulting elements (lighter, heavier )

14. Complete the following by filling in the blanks with the terms : fission, fusion, neither fission nor fusion, both fission and fusion.

( a ) Uses uranium-2 35 or plutonium as a nuclear fuel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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( b ) Uses hydrogen or lithium as nuclear fuel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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( e) Releases vast amounts of energy. .

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( f ) Type of nuclear reaction responsible for the energy released by the stars . . . . . . . . . . . . . .

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( g) Reaction taking place in a nuclear reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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( h ) Possible future source of energy, once the problem of harnessing the reaction has been .

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( j ) Results in the formation of helium. . 15.

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Complete the following chart by placing the correct answers in the blanks provided. THE N UCLEAR R EACTOR

Major Part

Func tion

Description

Nuclear fuel Graphite Concrete Control rods

16. Why was the discovery of the nuclear particle called the neutron important in relation to atomic energy?

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D �ATE

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17.

Elements may be made into . . . . . . . . . . . . . . . . . by placing them in the atomic pile to be bombarded by neutrons.

18. Explain how the control rods regulate the energy production of the nuclear reactor. .

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19. If the control rods were drawn farther out of the reactor, what would happen to the rate chain reaction?

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20. What is meant by a "breeder reactor?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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21. What is a particle accelerator? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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22. Particle accelerators are primarily used for investigating atomic structure and creating . . . . . . .

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23. X-rays and radioisotopes may be used to study the effect of radiation on the . . . . . . . . . . . . which control the characteristics we inherit. 24. How may radioisotopes containing tagged atoms be used by industry?

25. What is meant by a "tracer?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Mu ltiple-Choice Questions In each of the following questions, circle the letter preceding the word or phrase that best

completes the statement or answers the question.

1. Radioactivity in an atom is the result of activity taking place in ( b ) the nucleus, (c) the entire atom, (d) a stable atom. 2.

( a ) the outer electron rings,

The scientist generally credited with first witnessing nuclear radiation was (a) Rutherford, ( b ) Marie Curie, (c) Roentgen, (d) Becquerel.

3. In 1 895, X-rays were discovered by Becquerel.

(a) Rutherford,

( b ) the Curies,

(c) Roentgen,

(d)

4. Some of the radiation emitted by uranium ore is due to the radioactive elements polonium and radium discovered by ( a ) Rutherford, ( b ) the Curies, ( c ) Roentgen, (d) Becquerel. NAME

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CLASS

D �ATE

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1 25

5. The scientist who discovered that matter could be transformed into energy as the result of atomic disintegration was ( a ) Ernest Rutherford, ( b ) James Chadwick, (c) Otto Hahn, (d) Fritz Strassmann. 6. In 1 932, the neutron was discovered by (a) James Chadwick, ( b ) Fritz Strassmann, (c) Otto Hahn, (d) Albert Einstein. 7. The sub-atomic particle that is used to bring about a chain reaction in a nuclear reactor is the (a) proton, ( b ) neutron, ( c ) electron, (d) none of these. S. Nuclear fuel is inserted into a reactor in tubes ( slugs ) made of ( a ) cadmium, (c ) aluminum, (d) carbon.

( b ) graphite,

9. Which of the following are particle accelerators? ( a ) cyclotron, ( b ) bevatron, (c) betatron, (d) all of these. 10. Scientists accurately measure the age of rocks by determining the rate of decay of uranium to ( a ) iodine, ( b ) carbon, ( c ) lead, (d) cadmium.

Matching Questions In the space at the left of each item in Column A, place the letter of the term or expression in Column B that is most closely related to that item.

Column

Column A 1. Matter and energy are different forms of the same thing 2. Number of waves or vibrations in a given time 3. Investigating chemical reactions in the body with tagged atoms 4. Treating cancer 5. Study of heredity 6. Investigating photosynthesis 7. Alpha and beta particles and gamma rays

B

a.

Radioactive iodine and cobalt b. Radiations resulting from nuclear reactions c. Jonas Salk d. Albert Einstein e. Wave length f. Enrico Fermi g. Geology h. Tracer research i. Carbon- 1 4 j . Genetics k. Desalting sea water I. Frequency m. Cyclotron

S. Helped to create the first chain reaction 9. New source of fresh water

10. Machine used to accelerate particles used in atom smashing

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�A1vlE

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CLASS

]) �ATE

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Chapter

14

C I V I L DEFEN S E Despite the horror of nuclear weapons, many persons would survive a nuclear attack. This number would be increased if we were prepared to deal with the emergencies that arise from atomic explosions. Nuclear weapons may be classified as those which are dependent upon either the fission reaction, such as the atomic bomb, or the fusion reaction, such as the hydrogen or ther­ monuclear bomb. When a nuclear bomb is exploded about 2000 feet above the earth's surface, it causes the most damage and injury, resulting primarily from falling buildings and fire. Severe burns and radiation damage are also extensive. Surface bursts cause less damage than air bursts and fewer casualties from blast and fire, but the radiation danger is increased. Subsurface (underground) bursts result in the least damage, but radioactive fallout is increased. Underwater bursts also cause less damage, but radioactive water particles are carried long distances, as are other forms of atomic fallout, by prevailing winds. Atomic fallout is mainly dust and dirt, contaminated with radioactivity. It is odorless, tasteless and often invisible, thus increasing its potential danger. During a nuclear explosion, the energy re­ sulting from the destruction of matter is re­ leased in the following forms of energy :

1. Light. The light resulting from a nuclear blast may be hundreds of times brighter than that emitted by the sun and seen by us at the earth's surface. If you were to look directly into the blast (ball of fire ) , the intense light could destroy your eyes. 2. Blast. The blast or destructive force of nuclear explosions is usually measured in units called kilotons or megatons. A kiloton is equal to 1 ,000 tons of TNT. A megaton is

equal to 1 ,000,000 tons of TNT. Tremendous shock waves and violent winds traveling at great speeds add to the destructive force of the fir� bb�. 0 C

1 0 MI.

Zones of destruction. (5 megaton bomb

=

5 m illion tons of TNT)

Ring

Damage

A

Com plete destruction

B

Severe damage

C

D

Moderate damage Partial damage

3. Heat. The initial heat effect is of short duration, but at its center the temperature equals the temperature of the sun. The heat is so intense that it can ignite materials and in­ flict second-degree burns more than 25 miles away. This heat vaporizes large quantities of matter, forming radioactive fallout which is carried into the atmosphere and is spread by the wind. 4. Radiation (Radioactivity). Radioactivity is the emission of energy from an unstable atom ( radioisotope ) in the form of alpha and beta particles and gamma rays. The greatest danger resulting from this radiation is from gamma rays and free neutrons. These have great penetrating power and cause severe burns, radiation sickness, harmful mutations and death. Mutations are sudden changes in an organism due to a change in its gene structure 127

during the early development of an embryo. These mutations are usually harmful and are inherited by future generations. The first nuclear bomb was dropped on the city of Hiroshima, in Japan, during World War II. The bomb killed more than 70,000 persons and injured about 3 00,000. The total of 3 70,000 killed and injured with this single bomb would nearly equal the total population of Portland, Oregon. This explosion caused almost complete destruction of all buildings within a radius of three miles.

Substantial radiation, if spread over a longer period of time, can be tolerated. However, any large accumulation over even an extended period of time will be harmful.

Dose

Period of Exposure

600 r. 600 r.

Few days Long period

Effec t Death No permanent ill effects

3. Particle Size. Heavier particles settle more quickly and produce local fallout. Lighter particles are carried to great heights and spread great distances. Thus, many of the radioactive materials have sufficient time to disintegrate completely before they settle back to earth.

Approximate radiation dosages, received over a few days, and their effects, are listed below: 25- 1 00 roentgens - no effects to mild ill­ ness (nausea, some blood changes) 1 00-200 roentgens - mild to moderate ef­ fects as above 200-400 roentgens - serious illness, death in about 25 % of cases 400-600 roentgens - death in about 50 % of cases Above 600 roentgens - Most cases do not survive.

4. Absorption. A large dose of radiation over a short period of time will cause death.

Protective Measures Against Radioactive Fall­ out. The three basic principles underlying fall-

Factors Influencing Radioactive Fallout 1. Type of Bomb. Fission or atomic bombs produce more radioactive fallout than fusion or hydrogen bombs. 2. Type of Blast. A surface blast results in more fallout than an atmospheric burst.

I

�� ;:t.--;-e--i -. /FIS ION AND\ RADIOACTIVITY PAPER . //

Penetrating power of n uclear particles and rays.

- - - - alpha particles (+) l ittle penetration beta parti cles ( ) slight penetration � gam ma rays (0) g reat penetration -

• • •

128

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out protection are : ( 1 ) shielding, (2) distance from source of radioactivity, and (3) time fol­ lowing nuclear explosion.

1. Radiation Is Reduced by Shielding. The greater the amount and weight of the material between you and the radioactive source, the safer you will be. Well-built fallout shelters are essential. The protection factor, a measure of the amount of radiation that can pass through a specific shielding, is important. The minimum protective factor is 1 00. This will reduce the radiation behind the shielding to 1 � 0 th or 1 % of the radiation in the sur­ rounding area. Eighteen inches of concrete and 25 inches of earth will provide this minimum protection.

2. Distance. The greater the distance from the radioactive material, the less intense will be its effects. Radiation is measured in units called roentgens (r) and the intensity of radia­ tion is measured in roentgens per hour. Study the chart below. How is the relationship of intensity of radiation to distance similar to the Law of Illumination, studied in Chapter 1 1 ? Distance from Radiation Source

Radiation Intensity

1 00 ft. 200 ft. 300 ft.

1 600 r. 400 r. 1 78 r .

3. Time. The time it takes for half of the atoms of a radioactive material to disintegrate is called its half-life. Half-lives are constant for each radioisotope and range from mil­ lionths of a second to billions of years. The amount of radioactivity following a nuclear explosion decreases with time. In the first few days after the explosion, the short­ lived radioactive isotopes, such as iodine- 1 3 1 , are most dangerous. Strontium-90, another radioactive isotope, is a long-term radioiso­ tope; its long half-life is 25 years. Many radio­ active substances, such as strontium-90, may cause cancer and other harmful effects in humans. Radioactive Isotope Iodine-131 Strontium-90 Carbon-14

Half-Life 8 days 25 years 5 , 600 years

Possible Danger Cancer of the thyroid Leukemia Other Cancers

Plans and advice for constructing such shel­ ters can be obtained free of charge from your local Office of Civil Defense. Here are some of the minimum requirements recommended by the Office of Civil Defense for a shelter.

Basement Fallout Shelter 1. Food and Water. A fallout shelter should

Basement fallout shelter. 1 29

have sufficient water and food to maintain each person for a period of two weeks. This includes 7 gallons of water per person. Food should be in cans or unopened dustproof containers which need no refrigeration. Foods should be in quantities that can be eaten in one meal, and they should provide a well-balanced diet. Thirst-producing foods rich in salt should be avoided. 2. Battery-operated radio and flashlight should be at hand - with extra batteries.

3. Containers for human waste should be placed outside, but close to the shelter. 4. Instruments to measure radiation: a. Dosimeter: Indicates the amount of accumulated radioactivity. b. Dose rate meter: Indicates levels of existing radiation. 5. First aid supplies and first aid manual. 6. Blankets and clothing.

Decontamination (Removal of Radioactive Fallout). Contaminated clothing should be re­ moved. The person should wash thoroughly with soap and water to remove any radioactive material. Warning of Attack. Sirens, radio and television will be used to warn the public of possible attack. SELF-DI SCOVERY ACTIVITY

Constructing an Inexpensive Device to De­ tect and Measure Atomic Radiation. Materials: One I O-oz. drinking glass, a lid from a tin can, regular-weight aluminum foil, transparent tape, white nylon ( not cotton ) thread, black pocket comb, hammer, nail, 2 5-cent coin, scis­ sors, tableknife with a smooth handle and a I 5-inch ruler or a yardstick.

7. Reading and other recreational material. S. Soap, disinfectants and insecticides. 9. Basic tools, such as shovel, hammer, screwdriver, pliers, can openers, etc.

WARNING SIGNALS

Alert Signal (steady)

Take Cover (warbling)

AU Clear &

Warning in School

130

A steady sounding of the siren or other device for three minutes.

Procedure: 1 . Line the glass with aluminum foil. Cut a sheet of aluminum foil to measure about one square foot. Roll this sheet around the outside of the glass completely covering the sides and the bottom of the glass with foil. Slip the glass from its foil covering. Carefully ease the shaped foil inside the glass, molding it to the inside of the glass with the handle of the knife. The foil should hug the inside walls and bot­ tom of the glass.

A series of short blasts for three minutes. This indicates imminent attack and there is only time enough to reach the shelter. All-clear signals will not be sounded on public warning de­ vices. Radio and public address systems will be used. Students must obey the direc­ tions given by school authorities to assure greatest safety.

2. Cut windows. Remove the molded foil. Measure down from its top and make marks on the side at two and three inches. Cut a one-

inch square from 'the foil between the two marks. On the opposite side of the molded foil, repeat the measurements and cut out another one-inch square. Return the foil to the inside of the glass. When the glass is held at eye level, you should be able to see through the two windows.

3. Fasten the scale to the glass. Use an un­ lined sheet of paper to make an exact duplicate of the following scale. Be accurate in your

1l!1! I nIH

measurements. Secure your duplicate with transparent tape to the outside of the glass, placing it horizontally just below one of the windows so the top of the scale is at the bottom of the window. 4. Prepare lid. With the hammer and nail, punch two holes close together one inch from the center of the lid of the can. Two inches directly across the lid from these holes, punch two more holes. 5. Make the radiation indicators. Using the 2 5-cent coin as a pattern, cut out two circles of aluminum foil. Cut two lengths of nylon thread each about 1 5 inches long. Be careful to touch only the ends of the threads. Stretch out the two threads parallel and almost touching on the yardstick

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so they can be measured at the same time. Do not cross or tangle them. Measure off 5 -inch lengths near the center of the two threads. Anchor them to the yardstick with two short strips of transparent tape. Place the strips of tape just inside the 5-inch lengths of thread so that 5 inches are held taut against the ruler, leaving 5 inches of thread extending from each side. Insert a knife beneath the center of one of the 5-inch lengths. Raise the thread slightly, but do not touch it with your fingers. Slide one of the quarter-sized cir�les of aluminum foil beneath the knife. Remove the knife, allowing the thread to drop onto the foil. Fold a small edge of the foil circle back over the thread to attach it. This foil should be only one-half inch long, just enough to hook the foil to the threads. Don't touch the thread except at the ends. Moisture changes the reading. Attach the other quarter-sized circle of foil to the other thread in the same way. Tie the two parallel threads to each other at each end and pull each knot down tightly so that it falls exactly at the transparent tape at each end of the 5-inch lengths. Then make double knots to secure the first knots. 6. Install the indicators. Insert one set of the loose ends of thread through the two holes on one side of the lid. Pull the threads up as far as they will go and tie them on top of the lid. Remove the tape on that end. Then do the same thing with the other set of loose ends.

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131

Next, remove the anchor tapes holding the threads to the yardstick. You should now have two loops of thread hanging below the lid, with a foil disk dangling from each loop. Slide the foils on their threads so they hang at the bottom of the loop, oppo­ site each other. 7. Take a reading. Create static electricity by rubbing the pocket comb through your hair or against wool. Then brush the comb against each aluminum indicator. Repeat until static electricity separates the indicators by about one-half inch. Place the lid on top of the alumi­ num-lined glass, allowing the separated indi­ cators to hang freely inside without touching. Look through the window above the scale. Turn the lid until you see the thin edges, not the sides, of the round indicators. Place the device on a table about two feet from your eyes . Move the lid until each indicator points to the same number on either side of the scale. Take a reading by timing the number of

132

seconds needed for the bottom edges of the two indicators to move together over one full num­ ber on both sides of the scale. Multiply this number by 1 0 to find out how many hours you can be exposed to radioactivity at that level before receiving a lethal dose. A reading of 600 seconds would indicate no radiation danger. Your test reading today probably will be 1 0 to 3 0 minutes, indicating that the instrument is not being influenced by large amounts of radiation. After a nuclear ex­ plosion it might take only 1 3 seconds for the indicators to cover the distance between 4 and 3 on both sides of the scale. This would mean that the radiation you would receive in that location in 1 30 hours would be deadly if the radiation level remained constant. A series of readings would gauge diminishing danger from the radiation. Radioactive substances decay and the danger from their radiations decreases, so that despite a high initial reading, you might receive only a small percentage of a lethal dose over a period of several weeks.

R EVIEW TESTS Completion Questions For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement. 1. The "atomic bomb" is dependent upon a

reaction. The hydrogen bomb is dependent

upon a . . . . . . . . . . reaction. 2. What is meant by the term "atomic fallout?"

3. Why is atomic fallout difficult to detect? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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4. Atomic fallout is often carried long distances by . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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5. Why is the light resulting from a nuclear explosion dangerous? . . . . . . . . . . . . . . . . . . . . . . . . .

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6. What tremendous forces add to the destructive force of the initial blast of a nuclear explosion?

7. What is the meaning of the term "radioactivity?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8. What is a mutation?

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9. What type of nuclear bomb produces the largest amount of radioactive fallout? . . . . . . . . . . . .

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. nuclear particles have a greater chance of undergoing radioactive decay because they

will remain in the atmosphere for longer periods of time before they settle back to earth. 11. What is the meaning of the term "half-life?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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12. Half-lives range from . . . . . . . . . . . . of a second to . . . . . . . . . . . . of years. 13. During the first few days following a nuclear explosion, the . . . . . . . . . . . . . . . . radioactive isotopes such as NAME

are most dangerous.

_______

CLASS,

---'-' OATE

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133

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14. Why is radioactive strontium-90 dangerous? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

15. Give the half-life of the following radioactive isotopes : (a) iodine- 1 3 1 . . . . . . . . . , ( b ) stron.

tium-90

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16. A large dose of radiation, within limits, may be tolerated providing it is

17. The greater the . . . . . . . . and . . . . . . . . of the shielding between you and the radioactive source, the safer you will be.

18. What is the meaning of the term "protection factor?"

19. If you were building a fallout shelter for your family, how many inches of concrete would provide the minimum recommended protection factor of 1 00? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

20. List five characteristics of the food that should be placed in a well-supplied shelter. ( a ) ·

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23. If you became contaminated with radioactive fallout, what steps would you take to remove this dangerous material? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

24. Describe each of the following warning signals to be used in case of enemy attack. (a) Alert signal : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ·

1 34

.

. . .. . .. . . . . .. . .. . .

NAME

( b ) Take cover : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

_______

CLASS

DATE.

_ _ _

....

.

.

_ _ _ _ _ _ _ _

·

. . . . . . . . . . . . . . . . . (c) All clear : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . '

25. Why is it important that you obey directions given by school authorities in case of warning of enemy attack? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . : . . . . . . . . . . . . . . .

Multiple-Choice Questions In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question. ' 1. The hydrogen bomb is sometimes referred to as the ( a ) fission bomb, ( b ) thermonuclear bomb, (c) incendiary bomb, (d) clean bomb. 2. What type of hazard is increased when an atomic blast takes place at or below the surface rather than high in the air? (a) falling buildings, ( b ) fire, ( c ) fallout, (d) blinding by the blast.

3. A l a-megaton bomb is equivalent to ( a ) 1 0,000,000, ( b ) 1 0,000, ( c ) 1 ,000,000, (d) 1 00,000 tons of TNT. 4. If a 5-megaton bomb were dropped, severe damage would take place within a radius of (a) three, ( b ) ten, ( c ) six, ( d) thirteen miles.

5. Which type of nuclear radiation has great penetrating power and may produce future mutations? (a) alpha, ( b ) beta, ( c ) gamma, ( d) delta. 6. Which nuclear particle would penetrate paper but would not penetrate completely through the body? (a) alpha, ( b ) beta, (c) gamma, (d) delta. 7. The nuclear particles which would have a greater chance of undergoing radioactive decay before returning to earth are the (a) heavy particles, ( b ) light particles, ( c ) size makes no difference, (d) none of these. S. Radiation effects reduce with of these.

( a ) time,

( b ) shielding, ( c ) distance from explosion, (d) all

9. The unit used to measure nuclear radiation is called a ( a ) kilogram, ( b ) pound, (c ) roentgen, (d) centimeter. 10. If the distance from the source of radiation were increased from 1 00 feet to 200 feet, the intensity of radiation would be ( a ) four times less, ( b ) two times less, ( c ) four times greater, (d) two times greater. 11. The minimum protective factor suggested by the U.S. government in building a fallout shelter is (a) 10, (b) 15,000, (c) 100, (d) 400. 12. A fallout shelter should contain at least two weeks' supply of food and (a) 10, ( b ) 4, ( c) 7, (d) 2 gallons of water per person. 13. An inexpensive instrument which can measure existing levels of atomic radiation is a (a) dosimeter, ( b ) battery, (c) dose rate meter, (d) cloud chamber. 14. The removal of radioactive fallout is called, (a) cleansing, ( b ) decontamination, (c) disinfect­ ing, (d) extermination. 15. After an enemy attack, we would probably hear the all-clear signal from (a) our radio, ( b ) word of mouth, (c) our public warning devices, (d) block wardens. NAME

_______

CLASS

D.. ATE ....

_ _ _

_ _ _ _ _ _ _ _

135

Matching Q uestions In the space at the left of each item in Column A, place the letter of the term or expression in Column B that is most closely related to that item.

Column B

Column A a.

Dosimeter b. Alpha particles c. Portland, Oregon d. Civil defense e . Mutation f. Hiroshima g. Fallout h. Beta particles i . Strontium-90 j. Iodine-1 3 1 k. Protection factor of 100 I. Radioactivity

1. Particles which have little penetration power 2. Radioactive material resulting from a nuclear explosion 3. 3 70,000 killed and injured from nuclear bomb 4. A sudden change in an organism due to damage to genes 5. Negative nuclear particles resulting from radioactivity 6. Cancer of the thyroid 7. Will reduce radiation to 1 % of the surrounding area

8. Half-life of 25 years 9. Energy emitted from unstable atoms undergoing fission 10. Measures accumulated radioactivity

136

NAME

______

CLASS,

D u ATE

______

_ __ __ __ __ __ __ __

Chapter

15

T H E C H E M I STRY O F M ATTER The world w e live i n i s full of the wonders of chemistry. The results of chemical research are found in nearly every manufactured prod­ uct we use. Chemistry plays a role in the production and processing of food, in home construction and furnishing, transportation, communication, health and defense. Our very lives depend upon a chain of chemical reac­ tions in our bodies and in our environment. Chemistry is the study of the composition of matter and the chemical changes that take place in matter. Matter is anything that occupies space and has mass. . Mass is the amount of material in a sub­ stance. Weight is the measure of the gravitational attraction on the mass of an object. Weight is a characteristic of matter only when gravitational attraction is present and significant.

Branches of Chemistry. The over-all study of chemistry is divided into a number of special branches of study. Some of these are : 1 . Inorganic chemistry the study of non­ carbon substances . 2 . Orgq.nic chemistry the study of sub­ stances containing carbon. 3 . Qualitative chemistry the study of substances to determine what they con­ tain. 4. Quantitative chemistry the study of substances to determine how much of a particular material is present. -

-

-

-

5 . Physical chemistry the study of the physical laws that apply to chemical changes. the study of the chemi­ 6. Biochemistry cal processes of living organisms. -

-

Kinds of Matter. All the various forms of matter we come in contact with are classified into three types according to their composi­ tion: ( a ) elements, ( b ) compounds, and ( c ) mixtures. Elements and compounds are pure materials since they are composed of the same type of material throughout and their composition never varies. Such pure materials are called substances. Mixtures are composed of different kinds of materials and their composition may vary. ELEM ENTS

Elements are substances which contain only one kind of atom and cannot be broken down into simpler substances by ordinary chemical means. Chemists classify elements into two groups based upon their occurrence and their properties : ( 1 ) natural and synthetic, and ( 2 ) metals and non-metals. 1. Natural Elements. These are the elements found in nature. Surprisingly, the millions of kinds of materials that we see around us are composed of only 92 naturally-occurring elements . Of these 92, only 8 make up ap137

MOST COMMON ELEM ENTS IN THE EARTH'S CRUST

Element

Percentage

Oxygen

46.43

Silicon

27.77

Aluminum Iron

8.14 5.12 3.62 2.85

Calcium Sodium Potassium Magnesium

2.60 2 .09

proximately 99 % of the earth's crust. Oxygen, the most abundant of these elements, makes up nearly one-half of the earth's crust and about one-fifth of the atmosphere. Hydrogen and helium, rather rare gases on earth, make up most of the composition of the outer layers of the stars, including the sun, and most of the gas found in outer space between the stars. Few of these natural elements are found in the pure or free state ; they are usually found chemically combined with other elements. Chemists have developed a shorthand method for writing the names of elements. The ab­ breviations for the elements, which consist of one or two letters, are called symbols. If only

one letter is used, it is always written as a capital letter. If two letters are used, the first is written as a capital letter and the second as a small letter (see table below) . Such a system not only saves time, but also has the added advantage of being understood by scien­ tists all over the world. 2. Synthetic Elements. These are m an-made elements. Uranium, last on the list of natural elements, has an atomic number of 9 2. The atomic number of an element is the number of positively charg�st paxti.�les, called protons, fourur in-�iiie" nucleus or core o(an atom of that element. Synthetic elements that are heavier than uranium and have a higher atomic number ( more protons ) are called transuranium ele­ ments. Man has created more than twelve trans­ uranium elements so far. The American scien­ tist, Glenn T. Seaborg, and his associates, working at the University of California, have discovered many of the transuranium elements. Plutonium, one of these elements, has been used as an atomic fuel and a component in nuclear weapons. Research into the nature of synthetic ele­ ments may give man a greater insight into the mysteries of atomic structure.

SYMBOLS OF SOME I M PORTANT NATURAL ELEMENTS

138

Element

Symbol

Aluminum

Al

Gold

Au

Oxygen

0

Antimony

Sb

Helium

He

Phosphorus

P

Argon

Ar

Hydrogen

H

Potassium

K

Arsenic

As

Iron

Fe

Radium

Ra

Bismuth

Bi

Lead

Pb

Silicon

Si

Bromine

Br

Lithium

Li

Silver

Ag

Calcium

Ca

Magnesium

Mg

Sodium

Na

Carbon

C

Manganese

Mn

Strontium

Sr

Chlorine

CI

Mercury

Hg

Sulfur

S

Cobalt

Co

Nickel

Ni

Uranium

U

Fluorine

F

Nitrogen

N

Zinc

Zn

Element

Symbol

E1�ment

Symbol

Elements may also be classified in two divi­ sions based on their properties : ( 1 ) metals, and ( 2 ) non-metals. Most metals are ( 1 ) solid at ordinary tem­ peratures, and ( 2 ) have a metallic luster. They are ( 3 ) good conductors of heat and electricity, ( 4 ) have a high density ( weight per unit volume) , and ( 5 ) can easily be ham­ mered or drawn into different shapes. Some common metals are iron, aluminum, copper, silver and mercury. Mercury is the only metal that is a liquid at room temperature. TRANSURANIUM ELEMENTS

Atomic Number

Element

SOME COMMON COMPOUNDS

Compound

Formula

Water Sodium chloride (table salt) Carbon dioxide

H2O NaCI CO2

Carbon monoxide Sugar (glucose) Hydrochloric acid Sulfuric acid Nitric acid Sodium hydroxide (lye) Iron sulfide

CO C 6H120 6 HC 1 H2SO4 HN03 NaOH FeS

Symbol

93 94

Neptunium Plutonium

Np

95

Americium

Am

96 97 98 99

Cm

1 00 101 1 02 1 03

Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium

1 04

Rutherfordium

105

Hahnium

Pu

Bk Cf Es Fm

Md No Lw Rf

Ha

Non-metals are ( 1 ) generally poor con­ ductors of heat and electricity, ( 2 ) have a low density, and ( 3 ) may have a characteristic color. Some common examples of non-metals are sulfur (yellow) , carbon ( black ) , oxygen ( colorless ) , chlorine (yellow ) and bromine ( reddish-brown) . Bromine is the only non­ metal that is liquid at room temperature. C O M P O U N DS

Compounds are pure substances formed by the chemical union of two or more different kinds of elements, in definite proportions by weight. As a result of this union, the com­ pound has entirely different properties from the original elements of which it is formed.

The chemist's shorthand for a compound is called a formula. It consists of two or more symbols which represent one molecule of an . element or a compound. A molecule is the smallest part of a substance having the proper­ ties of the substance.

Mixtures are materials formed when sub­ stances of any kind are physically mixed with no chemical activity taking place. No new substance is formed and each substance re­ tains its original properties. These substances may be mixed in any proportion. Some ex­ amples of mixtures include air ( a mixture of gases) , a solution of sugar and water, and cream mixed in coffee. MAJOR DIFFERENCES BETWEEN COMPOUNDS AND MIXTURES

Compound

1. Chemical union

Mixture

1. Physical union

2. Elements unite in definite proportion by weight

2. No definite pro­ portions

3. New substance with new properties is formed

3. N o n e w s u b ­ stance formed

4. Can be separated by chemical means

4. Can be separated by physical means

139

4. Holding the tube in the test tube holder, heat the mixture until it glows with a red col­ or for a few minutes. Cool the test tube and carefully break it after wrapping it in a strong cloth.

SELF-DISCOVERY ACTIVITY

Problem: Investigating Some Differences Mixtures and Compounds.

Between

GRAMSFUR OFOF SULIGRAMS RON FILINGS

4

Materials: Powdered sulfur, iron filings, balance, tea­ spoon, test tube, bar magnet and test tube holder.

Procedure:

+

7

5. Observe the color of the reSUlting sub­ stance and the effects of bringing the magnet close to the material.

1. Use a teaspoon to obtain some fine iron filings and sulfur and record their colors.

Was any new substance formed? . . . . . . . .

IRON FILINGS

SULFUR

Color : . . . . . . . .

Color:

How do you know? . . . . . . . . . . . . . . . . . . . . . . .

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Conclusions: 1. What did you produce from the iron and +

SULFUR IRON FILINGS

2. Thoroughly mix these together on a dean sheet of paper and bring the bar magnet close to the mixture. Observe.

sulfur in step 2 of the procedure? . . . . . . . . . .

2. What did you produce from the iron and

sulfur in step 4 of the procedure? . . . . . . . . . .

Was any new substance formed? . . . . . . . . . How do you know? . . . . . . . . . . . . . . . . . .

3. Why do you suppose you were asked to weigh carefully specific amounts of iron and sulfur in the second part of your investigation?

3. Carefully weigh out 5 grams of sulfur and 1 0 grams of iron filings and mix them thoroughly together in a test tube.

140

NAME,

______

CLASS,

� DATE

_ _

_ _ _ _ _ _ _

R EVIEW TESTS Completion Questions For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement. .

1. What is chemistry?

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2. If a chemist had to find out what substances were present in an unknown sample he would work in a branch of chemistry called . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

3. If a chemist were asked to find out how much iron was present in a sample of a substance he would work in a branch of chemistry called 4. What is the difference between "weight" and

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"mass?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

s. Why is weight not always a characteristic of matter, although mass is? . . . . . . . . . . . . . . . . . .

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6. What is matter? . . . . . . . . . . . . . . . . . . . . . . . .

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7. What are three categories into which all matter found on earth may be classified according to its composition? ( 1 )

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(2)

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8. Synthetic elements higher than uranium in atomic number are called . . . . . . . . . . . . . . . . . elements.

9. What does a chemist mean by the "atomic number" of an element? . . . . . . . . . . . . . . . . . . . . . . .

NAME

______

CLASS,

D �ATE

__ __ __

__ __ __ __ __ __ __ _

141

10. Give the correct symbol for the following elements :

(a) copper

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(d) uranium

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( b ) hydrogen

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( e ) magnesium

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(c) mercury

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(f) strontium

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( h ) phosphorus

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( i ) gold

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•

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(g) aluminum

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11. Name the compound represented by each of the following formulas:

(a). CO2

•

•

( b ) H2S04

•

•

•

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•

•

•

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•

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(c) HN03

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(d) NaOH . . . . . . . . . . . . . . . . . . . . . . . . . . . .

12. Tell whether the following are examples of elements, compounds or mixtures ( use the letter E to represent an element, C a compound, and M a mixture ) .

(a) silicon

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( b ) muddy water

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( c ) HCI

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(d ) air

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(g) sugar

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(e) table salt

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( f ) copper

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( h ) pure water . .

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( i)

salt water

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....

13. Complete the following chart by filling in the blanks : Non-Metals

Metals

Characteristics Conductors of heat Conductors of electricity Density Ability to be hammered or shaped

14. Tell whether the following are examples of metals or non-metals :

(a) iron

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( b ) carbon

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( c ) sodium

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(d) chlorine

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( e ) mercury

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(i) bromine

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oxygen

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(n

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...

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( I)

magnesium

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( f ) aluminum

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(g ) sulfur

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( h ) lead

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( k ) carbon dioxide .

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15. Explain the difference between a compound and a mixture in terms of the following characteristics :

(a) Type of union.

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( b ) Type of proportions. . .

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(c) Type of formation. . .

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1 42

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NAME ______ CLASS,

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D �ATE

__ __ __

.

______________ _

Multiple-Choice Questions In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question. 1. Carbon compounds are characteristic of living material or material that was living at some time. The branch of science that specifically studies these compounds is called (a) qualitative chemistry, ( b ) organic chemistry, ( c ) quantitative chemistry, (d) physical chemistry. 2. A study of the chemical reactions taking place in living organisms is called (a) organic chemistry, ( b ) inorganic chemistry, (c) biochemistry, (d) physical chemistry. 3. Matter in a liquid state is characterized by which of the following? (a) spreads and fills all avail­ able space, ( b ) is rigid. ( c ) vibrates in a fixed position, (d) takes the shape of its container. 4. Pure matter, containing only one kind of atom, is called a ( an ) (a) element, ( b ) mixture, (c) compound, (d) substance. 5. How many natural-occurring elements are found on earth? (a) 28, ( b ) 63� (c) 92, (d) 1 04. 6. Nearly one-half of the earth's crust and about one-fifth of our atmosphere is composed of (a) nitrogen, (b) silicon, ( c ) carbon dioxide, ( d ) oxygen.

7. The smallest part of an element and the smallest particle which can take part in a chemical reaction is called a ( an ) ( a ) molecule, ( b ) atom, (c) neutron, (d) electron. 8. Matter which cannot be broken down into simpler substances by ordinary chemical means is a ( an ) ( a ) element, ( b ) compound, ( c ) mixture, (d) substance. 9. The most abundant metal on earth is (a) iron, ( b ) sodium, ( c ) aluminum, (d) potassium. 10. Which of the following is a man-made element? ( a ) neptunium, ( b ) rubber, (c) sulfur, (d) plastic. 11. The common name for sodium hydroxide is ( a ) table salt, ( b ) water, (c) lye, (d) bicarbonate of soda. 12. The transuranium element with atomic number 104 is called (a) americium, ( b ) einsteinium, ( c ) curium, (d) rutherfordium. 13. The only two elements, the first a metal and the second a non-metal, that are liquid at room temperature are ( a ) sodium and chlorine, ( b ) sodium and bromine, (c) mercury and chlorine, (d) mercury and bromine. 14. A chemical reaction must take place and form a ( an ) ( a ) compound, ( b ) element, (c ) mixture, (d) all of these. 15. The branch of chemistry that studies non-carb on substances is (a) qualitative, ( b ) inorganic, (c) organic, (d) quantitative. NAME._______CLASS

---DATE -LO

_ _

_ _ _ _ _ _ _ _

143

Matching Questions In the space at the left of each item in Column A, place the letter of the term or expression in Column B that is most closely related to that item.

Column B

Column A

a. Qualitative chemistry b. NaCI

1. The study of the physical laws underlying chemical reactions

2. Oxygen combines with iron to form rust

c.

Silicon d. C6H1206 e. Physical chemistry f. Quantitative chemistry g. Albert Einstein h. Glenn T. Seaborg 1. Heat j. Chemical reaction k. Oxygen 1. 92 m. 1 05 n. Lawrencium o. Uranium

3. Copper was present in an unknown substance 4. Discovered many transuranium elements 5. Exactly 5.6 per cent of sulfur was present in a substance 6. Inorganic compound

7. Most common element in the earth's crust 8. Needed to start a chemical reaction between iron and sulfur 9. Synthetic element

10. The total number of natural elements

1 44

NAME

CLASS,

_____ ._ _ _ _ _ _ _ _ _ _

DATE

___

_ _ _ _ _ _ _ _

Chapter

16

M AT T E R A N D E N ERGY

I

THE M O LECULAR TH EORY OF MATTER

different molecules, as when two objects are glued together, is called adhesion.

On a dark night as you peer into the sky you may wonder at the vastness of space occupied by the stars and other heavenly bodies. It may surprise you, however, to learn that matter itself is also largely space, and that it is composed of particles most of which are so small they cannot be seen even with our most powerful optical microscopes. These particles are called molecules. I Molecules are the smallest particles of a substance that retain all the properties of that substancef They are usually composed of two or more atoms chemically united. An atom is the smallest part of an element that enters into a chemical change. Water, for example, is composed of many water molecules, each molecule consisting of one atom of oxygen combined with two atoms of hydrogen. The water molecule has a slight negative + charge near the oxy­ gen atom, and a slight positive charge A water molecule near the hydrogen (dipolar). atoms . Molecules that have such a negative and positive charge are called polar or dipolar molecules. If a direct current of electricity is passed through water to which a little sulfuric acid is added to help conduct electricity, the mole­ cules of water will break apart or decompose into the elements hydrogen and oxygen in the ratio of two atoms of hydrogen to one atom of oxygen by volume. Molecules are always in a state of motion and are attracted to each other by powerful forces, primarily gravitational and electrical in nature. The force of attraction between similar molecules, such as water molecules , is called cohesion. The force of attraction between

1. States of Matter. Matter may exist in any of three states : (a) solid, ( b ) liquid, or ( c ) gas. The state of matter depends upon the energy available to overcome the cohesive forces that exist. A change in the state of matter is dependent upon a change in energy, usually in the form of heat or pressure. As more energy is added, often in the form of heat, molecular motion increases. A decrease in energy will lead to a reduction of molecular motion. 2. Properties of Matter. All matter pos­ sesses both physical and chemical properties. Most physical properties can be readily identi­ fied by direct observations using the senses only. Color, hardness, solubility, taste, state of matter, odor and density are some examples of physical properties. Chemical properties describe the behavior of a substance when it reacts chemically with another substance. Some examples of chemical properties are : ( a ) the ability to unite chemi­ cally with other elements or compounds, and ( b ) the changes in the chemical behavior of the substance when affected by heat, light, electricity and other forms of energy. The decomposition of water by electricity, the chemical union of oxygen and iron to form rust, burning, and the digestion of food are some examples of chemical reactions.

3. Physical and Chemical Changes. A physical change is a change in matter which does not produce a new substance; that is, no change in the chemical composition of the sub­ stance takes place. Examples of physical changes are : breaking glass, sawing wood, and dissolving sugar in water. A chemical change results in the formation of a new substance having new properties. A chemical change, therefore, results in, a 1 45

change in the chemical composition of the substance. Since different substances result, chemical changes are always accompanied by physical changes. The rusting of metals, burn­ ing and decay are some examples of chemical changes . 4. The Law of Conservation of Matter and Energy. As far back as the 1 8 th century, one of the basic laws dealing with matter and the changes occurring in matter was formulated by the French chemist, Antoine Lavoisier. This law, known as the Law of Conservation of Matter, stated that matter can neither be created nor destroyed in ordinary chemical reactions but may only be changed in form. In the 1 9th century, the Law of Conser­ vation of Energy was developed. This law, based upon many investigations, stated that energy can neither be created nor destroyed but may only be changed in form. Since then, the two laws have been combined Energy which states that in ordinary chemical reactions matter and energy can neither be created nor destroyed. Matter and energy are related and are ap­ parently different forms of the same thing. Al­ bert Einstein's equation, E = mc2 , tells us that matter contains tremendous amounts of energy and that under special conditions, such as nuclear reactions, matter can be converted into vast quantities of energy. This energy is referred to as "nuclear" or "atomic" energy. In Einstein's equation, E stands for energy, rn stands for the mass of the matter, c2 for the speed of light squared. Since the speed of light is approximately 1 8 6,000 miles per sec­ ond, it is obvious that the amount of energy in a tiny bit of matter is incredibly high. For example, there are 454 grams in one pound of matter and the amount of nuclear energy released by the conversion of just one gram of matter is equivalent to the energy released by the burning of 3000 tons of coal or 25 mil­ lion kilowatt-hours of electricity. Although under ordinary circumstances, matter and energy can neither be created nor

146

destroyed, they may be changed from one form to another. For example, the chemical energy of a battery can be changed into elec­ trical energy. Electrical energy can be changed into light energy in a light bulb, mechanical energy in a motor or heat energy in a toaster. A generator converts mechanical energy into electrical energy. Light is changed into chemi­ cal energy in the process of photosynthesis ( the food-making process of green plants ) or the taking of a photograph.

State of Matter

Characteristics 1 . Solids are rigid and have a definite shape and volume.

2. M o l e c u l e s v i ­ brate slowly i n a fixed position. 3 . M olecules are very close together. Solid. 1 . Liquids flow, take the shape o f their container and have a definite volume.

2. Molecules vi­ brate more rapidly and move farther ap art than in a solid. Liquid. o

0

o

0 , 0 0

0

1 . A gas will dis­ tribute itself uniform­ ly to fin all available space. This distribu­ tion is caned diffusion. 2. A gas has no definite shape or vol­ ume.

Gas.

5. Matter and Energy. Since matter is com­

posed of molecules which are in a constant state of motion, it is apparent that energy must be present. Energy is the ability to do work. Without energy molecular motion would cease. Energy is either added or given off in any physical or chemical change. The change of ice to water and water to gaseous water vapor, for example, involves the addition of energy to speed up molecular motion. The changing of a gas to a liquid results in the release of energy. Chemical changes which result in the re­ lease of energy are called exothermic reac­ tions. Most chemical reactions are exothermic. Chemical changes in which energy is absorbed and which require the continuous addition of energy in order to proceed, are called endo­ thermic reactions.

3. Dissolve and slowly heat 5 g. of pulverized salt in a beaker containing 20 milliliters of water. Stir the solution and, after it has cooled, taste a drop of the liquid and record the results.

Taste : 4. Heat some of this

solution in an evapo­ rating dish and boil until all the liquid is evapo­ rated. When cool, taste the residue in the dish and record the results.

20ML5 GRAMS. WATSAELRT SOLBMLU.TISALONT

+

{c( \. ,

Taste : Color:

SELF-DISCOVERY ACTIVITI ES

Conclusion: I. Exploring Physical and Chemical Changes.

1. What kinds of changes in matter did you

Problem: What are the characteristics of physical and chemical change and how do they differ from each other?

observe? . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

2. Support your conclusion . . . . . . . . . . . . .

Materials: Table salt, clean mortar and pestle, clean evaporating dish, clean beaker, balance, tripod, copper sulfate, strip of aluminum or an iron nail.

Procedure A: 1. Examine some table salt and record its color and taste.

�

Color: . . . . . . . . . . . . Taste : . . . . . . . . . . 1

PESTLE

� ::,7"

Color :

•

•

2. Pulverize some of the salt in a mortar and again record its color and taste. Taste:

Procedure B: 1. Prepare a solution of copper sulfate by adding 1 0 grams of copper sulfate to 1 00 ml. of water and then heat on low flame and stir.

ALUMISTRINUMP COPPER SOLUTIONSULFATE

2. After the solution has cooled, place a strip of aluminum in it. ( A strip of aluminum foil or a new shiny nail may also be used, although the aluminum metal strip is preferred. )

"

�

I

1 47

What kind of energy has been released in this reaction? . . . . . . . . . . . . .. . . . . . . . . . . . .

3. Record the following observations :

Color of Solution

Time

Appearance of Aluminum or Nail

2. Fill a 1 50 ml. beaker with 1 00 m!. of tap water, take the temperature and record it.

At the start

Temperature : . . . . . . . . . . . . . . After 1 5 minutes

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After 24 hours

Conclusions:

1. Do the reactions in Procedure B rep­ resent those of a physical or chemical change?

3. Slowly add 50 gms. of ammonium nitrate and stir until the salt IS dis­ solved.

THERMOMETERc::l STIRRI�lNG L

f1 MLG.. OFOFH20

4. After 2-3 minutes, record the following ob­ servations : ( a ) Touch the beaker. How does it feel?

1 00 + 50

AMMONIUM NITRATE

( b ) What is the temperature of the solu-

2. Support your conclusion. . . . . . . . . . . . .

tion? . . . . . . . . . . . . . . . . . . . . . . . . . .

Conclusions:

3. What is the coating on the aluminum or the nail and where do you believe it came from? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

1. Which investigation represented an exo­ thermic reaction and which an endothermic reaction? . . . . . . . . . . . . . . . . . . . . . . . . . . .

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I I . Exploring the Release of Energy in Exo­ thermic Reactions and the Absorption of Energy in Endothermic Reactions.

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2. Support your conclusions. . . . . . . . . . . Materials:

Matches, ammonium nitrate, balance, 1 50 ml. beaker, thermometer and stirring rod. Procedure:

1. Light a match. Observe the reaction and place your finger just high enough above the flame so as not to be burned. 148

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REVIEW TESTS Completion Questions For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement. 1. The three states of matter are ( a ) . . . . . . . . . . , ( b ) . . . . . . .

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. . , (c) . . . . . . . . . . . . . . . . . . . . . .

2. How would you investigate to see if sugar undergoes a physical or a chemical change when it dissolves in water? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3. The smallest particle of iron that possesses all the properties of iron is a ( an ) . . . . . . . . . . . . . . . . . . . 4. What are molecules? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5. Molecules are formed by the chemical union of smaller particles called . . . . . . . . . . . . . . . . . . . . . . 6. If a compound or a molecule is broken apart, it is said to be chemically

7. Tell whether the following are caused by cohesion or adhesion :

(a) a drop of water: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ( b ) sealing the flap of an envelope : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(c) gluing two pieces of wood together: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (d) water rising in a thin glass tube : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

( e) copper is a solid at room temperature : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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8. Why is an acid added to pure water before the water is to be decomposed with electricity? . . . . . . . . .

9. What does a chemist mean when he speaks of the diffusion of a gas? . . . . . . . . . . . . . . . . . . . . . . . . .

10. How does a chemical change differ from a physical change? . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

NAME

CLASS

______

�D �ATE

____

__ __ __ __ __ __ ___

149

11. Two chemicals were placed in a sealed flask. The weight recorded before they reacted was exactly .

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12. What is the difference between an exothermic and an endothermic reaction? . . . . . . . . . . . . . . .

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equal to the weight after the reaction. Explain these observations. .

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13. What must be added or taken away in order to bring about a change in the state of matter? . . . . .

14. Why are solids rigid? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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15. What are chemical properties? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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16. The basic law dealing with changes in matter was called the . . . . . . . . . . . . . . . . . . . . . . . . . . . .

17. What changes in the forms of energy are represented by the following? .

(a) generator : . . . . . . . . . . . . . . . . . . . . . . . . . . .

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( b ) photosynthesis : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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( c ) toaster :

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(d) photograph : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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( e) electric motor : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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( f ) gasoline engine : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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18. The nuclear energy of . . . . . . . . . . . . . . . . . of matter is equal to the energy released by the burning of 3000 tons of coal.

19. Complete the following chart by filling in the blank spaces : Substance

State of Matter

Molecular Speed

Distance Between Molecules

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iron rod

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water

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air

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20. How does the state of matter depend upon energy changes? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 50

NAME

_______

CLASS,

DATE

___

_ _ _ _ _ _ _ _

(a) E = (b) (e)

m =

c2 =

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= me! .

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21. Give the meanings of the symbols in Einstein's equation .

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23. The two agents most frequently used to bring about a change in the state of matter are . . . . . . . . . .

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22. Why will a strong odor soon spread to all parts of a room?

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24. Molecules of a solid do not move freely about but instead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

25. What happens when hot wax becomes solid? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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M ultiple-Choice Questions In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question.

1. The attractive force between similar molecules is called (a) adhesion, ( b ) cohesion, (e) magnetism, (d) none of these. 2. The attractive force between molecules of a particular state of matter is not strong enough to bind them together in a fixed position. For this reason they are capable of limited motion and will take .the shape of their container. This state of matter is ( a ) liquid, ( b ) solid, ( c ) gas, (d ) none of these.

3. All matter possesses ( a) physical properties only, ( b ) chemical properties only, (c) sometimes physical and at other times chemical propertie s, (d) chemical and physical properties at all times.

4. The water molecule is a dipolar molecule because it has (a) no electrical charge, ( b ) a positive electrical charge at both ends, (e) a negative electrical charge at both ends, (d) a positive charge at one end and a negative charge at the other.

5. If a molecule of water were broken apart, it would yield (a) two atoms of hydrogen for every atom of oxygen, ( b ) two atoms of oxygen for every atom of hydrogen, ( e ) one atom of hydrogen and . one atom of oxygen, (d) two atoms of hydrogen and two atoms of oxygen.

6. One type of energy that is used to decompose water is ( a ) mechanical, ( b ) electrical, (e) heat, (d) light. 7. As energy is added to matter, ( a ) molecular m otion and heat both decrease, ( b ) molecular motion and heat both increase, (e) molecular motion increases and heat decreases, (d) molecular motion de­ creases and heat increases.

8. What two forms of energy are observed in the burning of a match? ( a) heat and light, ( b ) heat and mechanical, (e) mechanical and light, (d) mechanical and electrical. NAME·

_______

CLASS,

DATE

___

_ _ _ _ _ _ _ _

151

9. All of the following are chemical properties except (a) reaction to bases, ( b ) reaction to acids, (c) reaction to pressure, (d) reaction to light.

10. All of the following are physical properties except ( a ) reaction in acid, ( b ) white color, ( c ) crys­ tal form, ( d ) sweet taste.

11. Which of the following is not just a physical change? (a) tearing paper, ( b ) digestion, (c) solu­ bility, (d) liquefying air.

12. Of the following, which is not a chemical change? ( a ) burning, ( b ) tarnishing of silver, (c) evapo­ ration, ( d ) souring of milk.

13. According to the formula E

= mc2, matter can be converted into ( a ) light energy, ( b ) heat energy, ( c ) chemical energy, ( d ) nuclear energy.

14. There are approximately how many grams in one pound? ( a ) 3 50, ( b ) 400, (c) 450, ( d) 500.

15. The solid state of matter is characterized by which of the following? ( a ) definite shape, indefinite volume, ( b ) definite shape, definite volume, ( c ) indefinite shape, indefinite volume, (d) indefinite shape, definite volume.

16. "The ability to do work" refers to ( a ) matter, ( b ) mass, (c) energy, (d) reaction. 17. Without energy molecular motion would ( a ) inc rease, ( b ) decrease, ( c ) cease, (d) remain steady.

18. Water vapor is water in the ( a ) liquid state, ( b ) gaseous state, (c) solid state, ( d ) none of these.

19. Light travels at the speed of approximately ( a ) 1 86 miles per second, ( b ) 1 8 , 600 miles per second, ( c ) 1 86,000 miles per second, (d) 1 8 6,000 feet per second.

20. Under ordinary conditions, m atter or energy can be ( a ) created, ( b ) destroyed, ( c ) created but not destroyed, (d) neither created nor destroyed.

Matching Questions In the space at the left of each item in Column A, place the letter of the term or expression in Column B that is most closely related to that item.

Column

Column A 1. Results in a release of energy 2. A form of energy 3. Carbon unites with oxygen to form carbon dioxide 4. Bending a metal rod

5. Decrease in molecular motion 6. Unite to form molecules 7. A stamp sticks to an envelope 8. Poor conductor of electricity 9. Mostly space

B

a. Physical change b. Atoms

c. Chemical change d. Adhesion e. Decrease in energy f. Cohesion g. Exothermic reaction h. Matter i . Pure water j. Sodium hydroxide k. Heat I. Two atoms of hydrogen and one of oxygen

10. A molecule of water

1 52

NAME _______ CLASS,___DATE

_ _ _ _ _ _ _ _

Chapter

17

C H E M I STRY A N D T H E ATOM Before man can accurately predict the prop­ erties and chemical behavior of elements he must first explore the structure of the atom. An atom is the smallest part of an element that possesses all the properties of that element. It is also the smallest part of an element that can enter into a chemical reaction. 1. Structure of the Atom. Until the end of the 1 9th century, scientists believed that the atom was the smallest possible structure of which matter was composed. In 1 8 97, the British physicist, Sir Joseph Thomson, dis­ covered that atoms contain smaller particles called electrons. Electrons are negatively charged particles that are found around the core or nucleus of the atom. The paths of these electrons are referred to as rings, shells, orbits, or energy levels. Energy level may be the most proper term because electrons change position depending upon the amount of energy present. Also, the "movement" of electrons is likely to be more of a vibration in a general area than a moving in a regular orbit, ring, or shell. The number and arrangement of these electrons determine the chemical properties of elements and compounds. Chemical reactions occur because of the lending, borrowing or sharing of electrons between atoms. In 1 9 1 9, the British scientist Sir Ernest Rutherford, discovered the proton, a positively charged particle in the nucleus of the atom. The proton is much more massive than the electron. It would take 1 , 840 electrons to equal the mass of a single proton. The number of protons in an element doesn't vary under usual conditions. An atom is normally electrically neutral or uncharged since the number of nega­ tive electrons in its orbits is exactly equal to the number of positive protons in the nucleus. In 1 932, the British scientist James C. Chadwick, discovered the neutron, another . particle in the nucleus of the atom. Since the neutron possesses no electrical charge, it is

neutral. This neutral particle has about the same mass as the proton. Thus, the nucleus of an atom is always positively charged, since the only electrically charged particles it con­ tains are the positive protons.

p e

n

ORBIENlNEG,RTGYSHEORLELVE,L ENEPROTON LEUCTRONTRON =

=

=

Hydrogen a tom.

Helium atom.

SUMMARY OF MAJOR ATOMIC PARTICLES

Particle Electron ( ) -

Proton

Characteristics a.

Negative charge ( - ) . h . Found in an area around the nucleus. c. Always equal in number to the protons in an uncharged atom. d. The number and arrangement of the electrons determine the chemical properties and behavior of elements. a.

Positive charge ( + ) .

b . Located in the nucleus.

c. The number of protons doesn't vary within the same kind of atom. d. They are always equal in num­ ber to the electrons in an un­ charged atom.

Neutron (0)

a.

Neutral or no charge.

b. Located in the nucleus.

2. Sub·Nuclear Particles. Atoms are so extremely small that it would take a row of 1 53

250,000,000 of them to measure one inch in length. In spite of this, scientists now realize that the nucleus alone contains other particles, many of which are smaller than either protons or neutrons. Some of these sub-nuclear particles are described below :

( a ) Positron. Has the same mass as an (+)

electron except that it pos­ sesses a positive charge.

( b ) Meson.

Intermediate in size between

( +, -

the electron and proton. This

or 0 )

particle

may

be

charged

having an atomic weight of 2 3 8 . The atomic weight of an element is equal to the sum of the protons and neutrons in its nucleus. Atom ic

Element Hydrogen

Weight (Mass) 1

1 proton, no neutrons (lightest atom)

Carbon

12

6 protons, 6 neutrons (standard of measurement)

Oxygen

16

8 protons, 8 neutrons (most common atom

positively, negatively or may be neutral.

( c ) Neutrino. A neutral particle with prac(0)

tic ally no mass.

( d ) Hyperon. More massive than either ( +, proton or neutron. This paror 0 )

ticle may have a positive charge, a negative charge, or may remain neutral.

In addition, there is recent evidence to establish the existence of matter made up of atoms containing structures which have op­ posite charges to all atomic particles. This matter is known as anti-matter. As an ex­ ample, there would be an anti-proton with a negative charge or an anti-electron with a positive charge. If such anti-matter and matter

Number of Protons and Neutrons

in earth's crust)

Uranium

238

92 protons, 1 46 neutrons ( heaviest natural atom )

Since atoms of elements unite in definite proportions by weight to form compounds, a knowledge of atomic weights helps the chemist determine the amount of the different substances entering into a chemical reaction.

collide, each would probably be destroyed, re­ leasing energy in the process.

4. Formula or Molecular Weight. Knowing the weight of a molecule of a particular com­ pound enables a scientist to determine ( a ) the percentage of elements present in the com­ pound, ( b ) the amounts needed to produce a solution having a certain desired strength, and ( c ) the weights of the materials that united to form the compound. The molecular weight (mass) is the sum of the atomic weights of all atoms comprising a specific molecule.

3. Atomic Weight. Since the greatest mass of an atom is found in the nucleus, atomic weight is based on the number of protons and neutrons in the nucleus. The atomic weight (mass ) of an atom is a relative weight in which the weight of a particular atom is compared to the weight of a chosen standard. The carbon atom, atomic weight 1 2, is used as the standard of comparison. Hydrogen is the lightest atom, having an atomic weight of 1 . Uranium is the heaviest natural atom,

Molecular (formula) weight can be deter­ mined by the following method : ( a ) List the elements present in the for­ mula of the compound. ( b ) Obtain the atomic weight of each ele­ ment by using the table of elements on pages 1 74- 1 75 . ( c ) Multiply the atomic weight of each element by the number of atoms of that element present ( subscript num­ ber) in a molecule of the substance.

154

( d) Add the total atomic weights. The sum is the molecular ( formula weight ) of one molecule of that compound. S. Atomic Number. The atomic number of

an element ur atom is the number of protons in the nucleus of the atom. Since an atom is electrically neutral, the atomic number is also the number of electrons outside the nucleus in the atom. No two elements ever have the same atomic number. The atomic number of hydrogen is 1 since it has only one proton and one electron. Uranium has the highest atomic number of the natural elements ­ atomic number 92. The trans uranium elements have atomic numbers higher than 92, present­ ly ranging to 1 0 5 . It i s the atomic number that enables scien­ tists to prepare an orderly arrangement of the elements that allows us to predict the proper­ ties of elements. Such an arrangement is called the Periodic Table of the Elements. The num­ ber of neutrons in the nucleus of an atom is found by subtracting the atomic number from the atomic weight. The atomic number is al­ ways the smaller of the two numbers. For example, lithium has an atomic weight of 7 and an atomic number of 3 . How many neutrons are present in the nucleus? Li atom

atomic weight = . atomIC number = . .

Neutrons present

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=

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Numher Element

Total

Atomic

of

Atomic

Weight

Atoms

Weight

H

1

x

o

16

X Molecular

Weight 6. Electronic Structure. It was previously stated that the chemical properties of an element depend upon the number and the arrangement of the electrons. To be more specific, one of the factors upon which the chemical behavior of an element depends is the number of electrons in the last or outer­ most ring farthest from the nucleus. The first ring ( shell, energy level ) closest to the nucleus is represented by the letter K, the second by the letter L, the third by the letter M, and so forth.

.

.

neutrons

SHELL 1 - K SHElL 2 - L SHELL 3 - M Sodium atom.

Examples:

Each ring can hold only a certain maximum number of electrons.

(a) NaCl

Element

Na Cl

Number of Atoms

Atomic Weight

23

35.5

X

X Molecular Weight

Total

Ring

Maximum Electrons

Atomic Weight

K

2

L

8

M

8

As seen above, the M ring can hold a maxi­ mum of 8 electrons. 155

Each atom tends to fill its outer ring so that it contains the maximum number of electrons. The electrons in the last ring are often referred to as valence electrons. Inert and active elements are terms that describe the degree to which elements combine chemically with other elements. Inert elements are elements which do not normally react with other elements since their outer rings contain the maximum number of electrons they can hold. All known inert elements are gases and include helium, argon, neon and the rare gases krypton, xenon and radon.

S03

- sulfite radical

SO.

- sulfate radical

PO.

- phosphate radical

NOs

- nitrate radical

N0 2

- nitrite radical

Remember the names of these radicals; they will help in reading the names of chemi­ cal formulas. Knowing the valences of the elements and radicals will help you under­ stand chemical behavior and is essential in learning how to write formulas and equations correctly. SELF-DI SCOVERY ACTIVITY Making a Model of Atomic Structure.

Materials:

Helium a tom.

Neon atom.

Active elements are elements whose outer rings are incomplete and which, therefore, tend to complete this outer orbit. These ele­ ments readily unite with other elements by lending, borrowing or sharing electrons in com­ pleting their outer orbit. The number of electrons which an atom will lend, borrow or share during a chemical change is called the valence of that element. Sometimes two or more atoms may pair up and behave as a single unit during chemical reactions. These groups of elements or atoms are called radicals and have their own valence just as any single element or atom would. Some examples of elements that join to form radicals are : - ammonium radical - hydroxide ( hydroxyl ) radical - carbonate radical HCOg - bicarbonate radical CI03

156

- chlorate radical

Pieces of bare copper or steel wire, wire cutters, pliers, tape, b alls of various soft mate­ rials, such as cotton wadding, styrofoam, clay or sponge rubber, and glue.

Procedure: Construct models of some of the atoms dis­ cussed in this chapter. If you wish, use the Periodic Table of the Elements on pages 1 74 and 1 7 5 , and construct models of some of the larger elements, such as lead. Discuss in class the parts of each model in terms of chemical properties. Make a display of the models for other classes to see.

Observations: 1. Which model in this chapter needs only 2 particles? . . . . . . . . . . . . . . . . . . . . . . . . . .

.

2. Which model will require 3 shells? . . . . .

3. Which model has only one shell, but has 6 particles? . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Which models are of inert elements? . .

.

R EVIEW TESTS Completion Questions For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement. 1. Why is matter usually electrically neutral? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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2. What is an atom? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3. Give the contribution of the following scientists :

(a) Sir Joseph Thomson. .

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( b ) Sir Ernest Rutherford. . . . . .

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( c ) James C. Chadwick. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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4. Complete the following chart by filling in the blanks. THE THREE BASIC ATOMIC PARTICLES

Particle

Electrical Charge

Location rings nucleus nucleus

5. What three other names are applied to the rings of an atom? . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6. What is the relation of atoms to molecules? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7. Today we realize that the atom is a highly complex structure whose nucleus alone may contain a great many sub-nuclear particles.

(a) Give- the characteristics of the following sub-nuclear particles :

NAME

( 1 ) positron: . . . . . . . . . . . . . . . . . . . . . . . . . .

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( 2 ) meson:

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CLASS,

D � ATE

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157

( b ) Name the sub-nuclear particle having the following characteristics : ( 1 ) A particle having no electrical charge and practically no mass. ( 2 ) A particle more massive than either t he size of the electron? (a) They are the same. ( b ) any electrical charge o r b e neutral.

8. What is anti-matter? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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9. What are valence electrons? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

,

10. Why is a knowledge of the number of valence electrons so important to scientists? . . . . . . . . . . .

11. Each energy level can usually hold only a certain maxi­

Energy Level

Maximum El�trons

1 st (K)

. . .

2nd (L)

. . .

3rd ( M )

. .

mum number of electrons. List the maximum number of electrons usually found in the following energy levels :

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12. If the outermost ring of an element has its maximum number of electrons, the element would be

chemically

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13. What is an active element? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

14. What does a chemist mean by the term "valence?"

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15. What are radicals? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

16. Give the name of the following radicals :

(a) OH

( c) NH4

( b ) S04

(d) CI03

(e)

P04

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•

17. How might a knowledge of the identification and names of the radicals help you?

158

NAME

______

CLASS

� DATE

__ __

__ __ __ __ __ __ __ _

18. How is the approximate atomic weight of an element determined mathematically? . . . . . . . . . .

19. In the space at the

right, make a diagram of the lightest of all elements.

Label

all

structures in the dia­ gram

and

give

the

name of the atom.

20. In what way is the structure of the atom of the lightest of all elements peculiar when compa.t:ed to .

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21. Why is a knowledge of the atomic weight of an element important to a chemist? . . . . . . . . . . .

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22. Atoms or elements unite chemically in definite proportions by . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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23. The weight or mass of a single molecule of a substance is called the molecular weight or the

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24. Why is a knowledge of the molecular weight or mass important to a scientist? . . . . . . . . . . . . . . . . .

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25. What is meant by the term "molecular weight or mass?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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26. What is meant by atomic number? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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27. Given the following information, draw

a diagram of the atom in the space provided: Given : atomic weight atomic number NAME

=

28

=

14

______

CLASS

D. ATE, ....

_ _ _

_ _ _ _ _ _ �

1 59

28. Give the electrical charge of the following atomic structures :

( a ) proton . . . . . . . . . . . . . . .

( b ) neutron . . . . . . . . . . . . . . .

( c) electron

29. The . . . . . . . . . . . . . . . . elements have an atomic number higher than 92. 30. No two elements ever have the same . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Multiple-Choice Questions In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question.

1. The central core of an atom is called the (a) nucleus, ( b ) neutron, (c) orbit, (d) electron. 2. Until the end of the 1 9th century, scientists believed that the smallest structure of which matter was composed was the ( a ) neutron, ( b ) electron, (c) molecule, (d) atom. 3. If an atom possessed 1 2 protons, how many electrons would be present? ( a ) 12, ( b ) depends upon the atomic weight, ( c ) depends upon the number of neutrons, (d) 1 3 .

4 . How does the mass of the proton compare to the size of the electron? ( a ) They are the same. ( b ) The electron is much more massive. ( c ) The p roton i s much more massive. ( d ) They are both too small to determine. 5. The second shell from the nucleus is the (a) L shell, ( b ) M shell, ( c ) N sheil, (d) K shell. 6. The M shell is usually capable of holding a maximum of (a) 2, ( b ) 8, (c) 10, ( d) 1 6 electrons. 7. Atoms tend to complete their outer orbit by all of the following except (a) borrowing, ( b ) lending, (c) sharing, (d) splitting.

8. Of the following which is not an inert gas? (a) krypton, ( b ) xenon, ( c ) nitrogen, (d) radon. 9. Which two particles are approximately equal i n mass? (a) proton and electron, ( b ) neutron and electron, ( c ) proton and neutron, ( d ) none of these.

10. The greater part of the mass and weight of the atom is found in the ( a ) nucleus, ( b ) outermost orbit, ( c ) orbit closest to the nucleus, (d) electrons .

11. In establishing the atomic weights of the elements, the atom that has been chosen as standard of comparison is (a) hydrogen, ( b ) carbon, ( c ) nitrogen, (d) helium.

the

12. Oxygen was at one time the standard of comparison for atomic weight. What is its atomic weight? ( a ) 1 6, ( b ) 8 , ( c ) 4, ( d ) 2. 13. If an atom had 1 7 protons, 17 electrons and 18 neutrons, its atomic weight was (a) 17, ( b ) 34, (c) 35, (d) 52. 14. Given the following information, determine the molecular weight of CUS04' Element

A tomic Weight

Cu S o

64

32 16

(a) 1 1 2, (b) 640, ( c ) 1 60, (d) 128. 15. Using your knowledge of symbols and radicals, determine the name of the above compound. (a) copper sulfate, ( b ) copper sulfite, ( c ) copper oxide, (d) sulfuric acid.

1 60

NAME

_______

CLASS

.. D..., ATE

_ _ _

_ _ _ _ _ _ _ _

Chapter

18

C H E M ICAL ACT I VITY One factor upon which the chemical prop­ erties and behavior of an element depend is the number of valence electrons present. As we have learned, an atom tends to complete its outer ring by obtaining the maximum number of electrons that the orbit can hold. To do this, atoms lend, borrow, or share electrons. It is this interchange or sharing of electrons that relates to the chemical activity of the elements.

1. Metals and Non-metals. Elements can be classified on the basis of their chemical activity as metals or non-metals . Metals con­ tain few electrons in their outer shell ­ usually less than four. Metals, and the non­ metal hydrogen, tend to lose electrons during a chemical reaction in completing . an outer shell. When this outer shell is complete it is said to be saturated. The atoms tend to saturate their outermost rings. The farther these elec­ trons are from the positive nucleus which at­ tracts them, the more easily they are lost. Since they lose negative particles, these elements ( metals and hydrogen) are said to be electro­ positive ( + ) The fewer electrons present in the outer shell of an atom of a metal, the more active the metal generally is. Sodium, for example, has only one electron in its last ring and is thus a very active metal. It will readily lend or share its valence electron in filling its outer ring of eight electrons and become saturated. Since the valence of an element represents the number of electrons lent, borrowed or shared by an atom of the element, it can be seen that sodium has a

Sodium atom (valence + 1 ).

metal is at the top of the table and the least active metal is at the bottom. This arrange­ ment is referred to as the Activity Series of Metals, the Electromotive Series of Metals, or the Electrochemical Series of Metals. It shows the similarities and differences in the behavior of metals. The chart below contains a partial list of metals to represent a sample of the activity series. ACTIVITY SERIES OF METALS Most Active

.

valence of + 1 , since it will lend or share one electron during a chemical reaction in saturating its outermost shell. The metals are often arranged in a table of decreasing chemical activity. The most active

0 m () :c m » (f) Z G) » () -i <

=i

1 -<

Potassium Sodium Calcium Magnesium Aluminum Zinc Iron Nickel Tin Lead

Always found in the form of compounds in nature.

}

Rarely found free or chemically uncombined.

HYDROGEN

Copper Mercury Silver Platinum Gold

Least Active

}

}

Often found in the free or chemically uncombined state. Almost always found in the free state.

1 61

Since a more active metal will replace a less active one below it in the activity series, this chart enables us to predict which metals will replace other metals during a chemical reaction. The more active metals lose their electrons more easily than the less active ones. Even though hydrogen is a non-metal, it appears in the electromotive series because it has only one electron . This electron may easily be lost during chemical reactions. Thus, hydrogen often acts as a metal during chemi­ cal reactions. Active metals above hydrogen will replace hydrogen from most acids ; those below hydrogen will not. Non-metals are elements which have many electrons in their outer ring or valence ring, generally more than four. Since non-metals need only a few electrons to complete their outer shell, they will borrow or share electrons from other atoms during a chemical reaction . Since they gain electrons, non-metals are said to be electronegative ( - ) . Generally, the larger the atom of a non-metal the less it will attract electrons, and the less active the non­ metal will be. The fewer electrons that a non-metal must borrow to complete its outer ring, the more active it will be. For example, chlorine has 7 electrons in its valence shell, thus it is a very active non-metal . Since chlorine gains 1 electron from another atom during a chemical reaction, it has a valence of - 1 .

Because all halogens have the same number of electrons in their outer valence shell, they all possess similar properties. All halogens have 7 valence electrons and thus will readily enter into chemical reactions by borrowing one electron in order to complete their outer ring. This gives them a valence of - 1 . The primary halogens include the elements fluorine, chlorine, bromine and iodine. These elements are also listed in a table or series of decreasing chemical activity. Fluorine is the most active and iodine is the least active. THE HALOGEN ACTIVITY SERIES (NON-METALS)

Fluorine (F) Chlorine (el) Bromine (Brl

Chlorine is a member of the halogen family, a group (family ) of very active non-metals. 1 62

gases liquid solid

Iodine (I)

Inert elements, as you have learned, do not normally enter into chemical reactions, since they already have a maximum number of electrons in their outer ring. These elements include the gases helium, argon, neon, kryp­ ton, xenon and radon. Valence Electrons Valence 8 saturated

7

Chlorine atom (valence - 1 ).

}

0

6 5

-1 -2 -3

4

±4

3 2 1

+3 +2 +1

Characteristics Inert Non-metals (borrow electrons) Metallic or nonmetallic Metals (lend electrons)

2 . Formation of Compounds and Ions. Compounds are formed by the lending, shar­ ing, or borrowing of valence electrons by atoms in completing their valence ring. Elements or radicals with metallic prop­ erties will lend electrons ; elements with non-

metallic properties will borrow electrons. If electrons are shared between two or more atoms, the resulting compound is referred to as a covalent compound.

HYDROGEN

x o

= =

HYDROGEN ENLEECLTRONECTRON HYDROGEN OXYGE

Water-a covalent compound.

If there is an actual transfer of electrons between the atoms of radicals in a chemical change, the atom or group of atoms becomes either negatively or positively charged. These atoms or radicals that have gained or lost electrons and have become charged are called ions. Unlike an atom which has the same number of protons and electrons and is, therefore, neutral, an ion does not possess equal numbers of protons and electrons. There are other facts that are true of ions : ( a ) Ions have a charge equal to the num­ ber of electrons they lend or borrow. This number is equal to the valence of the element. For example, when a neutral sodium atom ( 1 1 protons and 1 1 electrons ) loses one negative elec­ tron, it forms an ion with 1 1 protons and 1 0 electrons. The charge of the sodium ion is then + 1 . When a neutral chlorine atom ( 1 7 protons and 1 7 electrons ) borrows one negative elec­ tron, it forms an ion made up of 1 7 protons and 1 8 electrons. A chlorine ion, therefore, has a charge of - 1 . ( b ) Atoms and ions of the same element have different properties.

Element

Atom

Ion

Sodium

Reacts with H2O

No reaction with H2O

Copper

Red color

Blue color

( c ) Certain substances break up into ions when dissolved in water. This process is known as ionization or dissociation. The ability of a substance to carry an electric current is dependent upon its ability to form ions in solution. A substance which carries an electric current is called an electrolyte. The more ions formed, the greater the electric current carried by an electro­ lyte. Since covalent compounds are not composed of ions, they are non­ electrolytes. The chemical union of oppositely charged ions forms an ionic or electrovalent substance or compound. Thus, such compounds are formed by the transfer of electrons from one atom to another. This type of chemical union is called electrovalence.

Sodium ion + 1 .

Chloride ion

-1.

Sodium is an active metal with a valence of + 1 . Chlorine is an active non-metal with a valence of - 1 . A sodium atom will transfer its single valence electron to the chlorine atom , and, in this manner, the outer ring of both of these atoms becomes complete. This results in the formation of a positive sodium ion and a negative chlorine ion which attract each other, forming a stable crystalline compound, ordinary tSl-ble salt ( sodium chloride) . Crystals 1 63

are formed by groups of ions, arranged in a definite pattern called a crystal lattice. Internal view.

-

-l

External view. Salt crystal (NaCI)

3. Equations. An equation is a chemist's shorthand consisting of symbols and formulas which tell us what substances are reacting and what products are formed during a chemical reactiOn. If you remember, a symbol is the chemist's shorthand for an element. A formula represents one molecule of an element or compound. The two sides of the equation are separated by an arrow which is read as "yields, " "produces" or "forms ." Example of a chemical equation : Zn + zinc

Note:

t

2 HCI - ZnCb +

hydrochloric acid (Reagents ) =

zinc hydrogen chloride gas ( Products formed )

gas.

The large number written in front of a formula or symbol is called a coefficient. This number represents the number of molecules ( or parts ) of that substance present. If the coefficient is absent, it means one molecule. Thus, in the above reaction, 1 molecule of zinc and 2 molecules of hydrochloric acid united chemically to form 1 molecule of zinc chloride and 1 molecule of hydrogen gas. The small number is called a subscript and represents the number of atoms of a particular 1 64

element present in that formula. If no subscript is present, it means that 1 atom of that element is present. For example, in the formula H2 S04 , there are 2 atoms of hydrogen, 1 atom of sulfur and 4 atoms of oxygen in one molecule of sulfuric acid. A chemical equation, as you have just learned, represents a chemical reaction. Since all reactions follow the Law of Conservation of Matter and Energy, the same number of atoms of a particular element must be present on both sides of the equation. 4. Types of Chemical Reactions. It is im­ portant for a chemist to know the types of chemical reactions so that he will be able to predict the products that will be formed. Most chemical reactions may be classified in four main types : ( a ) combination or synthesis reactions, ( b ) analysis or decomposition re­ actions, ( c ) single replacement reactions, and ( d ) double replacement reactions.

( a ) Combination or Synthesis Reactions. In this type of reaction, two or more elements generally unite to form a single compound. Elements may com­ bine with elements or they may com­ bine with compounds. Compounds may also unite with other compounds. ( 1 ) Two elements combining : Fe + S iron + sulfur 6, Note: D = heat.

FeS iron sulfide

( 2 ) Two compounds combining : carbon dioxide

water

carbonic acid

( b ) A nalysis or Decomposition Reactions. In this type of reaction, a compound is broken down into simpler com­ pounds or into its elements. 2HgO mercuric oxide

t

2Hg + 02 mercury oxygen

(c) Single Replacement. In the single re­ placement reaction, a chemically more active element reacts with a compound to replace a less active element in the compound. As a result of the reaction, a new element and a new compound are obtained. Zn + CUS04 zinc copper sulfate

-

ZnS04 + Cu copper zinc sulfate

The zinc is more active than the copper in copper sulfate ( CUS04 ) and replaces it, setting copper free. Since this reaction illustrates the replace­ ment of a single element of a com­ pound by a more active element, it is referred to as a single replacement reaction. Do you remember an activity you did in Chapter 1 6 that illustrated single replacement? (d) Double Replacement. Sometimes two compounds react chemically to form two new compounds. This occurs when the elements in these compounds exchange places with each other. HCI + NaOH - NaCI + H2 0 hydrochloric sodium sodium water hydroxide chloride acid Picture this reaction between HCI and NaOH as two couples dancing, and then each partner exchanges places with the other. Since there is a double exchange of partners ( elements ) , this type of replacement is referred to as a double replacement reaction. SELF-DISCOVERY ACTIVITY

Investigating Electrolytes and Non-electro­ lytes. Materials: 6-volt battery, miniature socket and 4.5-volt bulb, bell wire, distilled water, tap water, dry sodium chloride (N aCI ) , water solutions of

sodium chloride, acetic acid ( CH3COOH) , sodium bIcarbonate (NaHCOs ) , sugar ( su­ crose ) ( C1 2H22011 ) , alcohol ( C2H50H) and beakers.

ITHESE TION OFREMWIOVERE.D FROMENLSULECTRODEAENDSBECOME S. SOLUTI TESTEDON TO BE Conductivity apparatus. (Connect as shown to test solutions.)

Procedure: Electrolytes conduct an electric current be­ cause they dissociate and form ions in solution. The movement of these ions conducts the current. Positive ions travel to the negative electrode ( cathode) and gain electrons. Nega­ tive ions travel to the positive electrode ( anode ) and lose electrons. Test the electrical conductivity of the dry salt and the solutions with the apparatus shown. Wash and dry the wire ends after each test and keep your hands dry. Connect the apparatus only after the electrodes are in the solution to be tested. If the bulb glows, a current is flowing and the material is an electrolyte. The brighter the glow the better the electrolyte. If there is no glow, the material is ei.ther a very poor electrolyte or a non­ electrolyte. In water solutions that are electro­ lytes, you may notice bubbles appearing at the electrodes. This is because the electrical energy begins to decompose the water into hydrogen and oxygen gas.

1 65

Observations: Complete the following chart:

Material Tested

Electrolyte Poor Good

Non-electrolyte

Dry NaCI Solutions of: Distilleq water Tap water Sodium chloride Sodium bicarbonate Acetic acid Sugar Alcohol

Conclusions:

3. The electric current is conducted by

1 . A substance which conducts an electric

charged particles called . . . . . . . . . . . . . . . . .

current when it is melted or in solution is

4. Organic substances contain the substance

called a( an ) . . . . . . . . . . . . . . . . . . . . . . . . .

carbon. Such substances are normally ( elec-

2. In order for a material to conduct an

trolytes, non-electrolytes ) . . . . . . . . . . . . . . .

electric current, it must dissociate in solution. Explain the meaning of this statement. . . . .

5. As the number of ions in solution in-

creases, the electric current . . . . . . . . . . . . . . 6. . .

.

.

. . . . compounds have no ions and

are non-electrolytes.

1 66

R EVIEW TESTS Completion Questions For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement.

1. The chemical properties of an element are dependent upon the . . . . . . . . . . . placement in its atoms. .

2. What is an electrolyte? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3. In one of the previous activities in this book, a piece of aluminum was placed in a copper sulfate

solution. What were the results? Give a scientific explanation for the reaction. .

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4. In the reaction between aluminum and the copper sulfate solution, the copper sulfate was originally a

blue-colored solution, and after the reaction was completed, the copper set free was a red color. What caused the difference in color between copper and copper sulfate? . . . . . . . . . . . . . . . . . . . . . . . . .

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5. What are the valence electrons? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. It is the number of valence electrons that determines the chemical activity of an element. Why is

this statement true? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7. Non-metallic elements are electronegative because they . . . . . . . . . . . . . . . . . . . . . . . . . . . electrons.

8. What are ions?

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9. What is meant by the valence of an element? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

NAME

_______

CLASS

___

�ATE

_ _ _ _ _ _

167

10. Below is a chemical reaction between chlorine and a compound called potassium bromide.

Clz + 2KBr chlorine potassium bromide

2KCI + Br2 potassium chloride bromine

(a) What type of chemical reaction does this equation represent? . . . . . . . . . . . . . . . . . . . . . . . . ( b ) Why does this reaction take place? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11. Silver tarnishes because it chemically unites with sulfur to form silver sulfide ( Ag2S ) . If tarnished

silverware were placed in a plastic pan containing some water and a piece of magnesium, what do you think might happen? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

12. At the right is a diagram of an atom. Answer the following questions relating to this atom.

(a) Is this a diagram of a metal or a non-metal? . . . . . . . . . . . . .

.

( b ) How many valence electrons are present in this atom? . . . . .

.

(c) What would be the valence of this element? . . . . . . . . . . . . .

.

(d) What is the atomic number of this element? ( e ) What is the atomic weight of this element? . . . . . . . . . . . . . .

.

( f ) What is the name of this element? . . . . . . . . . . . . . . . . . . . . .

.

13. Generally, the larger the atom of a non-metal, the (less, more ) will be its activity. 14. The (fewer, more ) electrons a non-metal must borrow to complete its outer shell, the more active

the element will be. 15. List the members of the halogen family in the order of their decreasing chemical activity.

(a) . . . . . . . . . . . . ,

(d) . . . . . . . . . . . . . . . . . . . . .

.

16. The halogen family is made up of a group of very active . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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17.

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(b )

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(c )

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Explain why chlorine gas could be bubbled through a solution of sodium bromide in order to obtain free bromine.

18.

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have a saturated valence ring and thus will not ordinarily enter into chemical reactions.

1 68

NAME

_______

CLASS

D �ATE

__ __ __

__ __ __ __ __ __ ___

19. Compounds are formed by the . . . . . . . . . . . , . . . . . . . . . . . or . . . . . . . . . of electrons between atoms during a chemical reaction. 20. Atoms that have gained or lost electrons during a chemical reaction are called 21. The chemical union of oppositely charged ions forms a ( an ) . . . . . . compound. 22. Explain why the addition of some salt or acetic acid to pure water will enable the water to .

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conduct an electric current. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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23. Define the term "electrolyte." . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

24. A metallic electrolyte will form . . . . . . . . . . . ions in solution, whereas a non-metallic electrolyte

wilI form . . . . . . . . . . . ions in solution. 25. Most common gases occur as diatomic molecules. Such

diatomic molecules are composed of 2 atoms which share their electrons and are thus united by a covalent bond. H2, O2, Cb, and N2 are common examples of such covalent molecules. Given the fact that hydrogen has 1 proton and no neutrons, draw a diagram of such a diatomic molecule of hydrogen gas in the box at the right.

Diatomic molecule of hydrogen gas.

Multiple-Choice Questions In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question. 1. During a chemical reaction, metallic elements will (a) lend electrons, ( b ) borrow electrons, (c) neither borrow nor lend electrons, (d) at times borrow and at other times lend electrons.

2. The extremely active metals and non-metals are usually found (a) combined with other elements, ( b ) free in nature, (c) sometimes free and sometimes combined, (d) it depends upon the specific

element.

3. Inert elements do not usually react to form compounds because (a) they have only one electron in

their outer ring, (b) they lack only one electron in their outer ring, (c) their outer ring is saturated, (d) none of these reasons is correct. 4. A non-metal that lends electrons is (a) oxygen, ( b ) carbon, (c) hydrogen, (d) helium. 5. In the activity series of metals, the most active metals are (c) near the middle, (d) closest to hydrogen. NAME

_______

CLASS,

___

(a) at the top, ( b ) at the bottom,

DATE.

_ _ _ _ _ _ _ _

1 69

6. During a chemical reaction, the more active the metal the more easily it will give up (a) proton�, ( b ) electrons, ( c ) ions, ( d ) all of these. 7. As the size of an atom of a metal increases, electrons are (a) lost more easily, greater difficulty, (c) attracted more easily, ( d ) attracted with greater difficulty.

( b ) lost with

8. The halogens will enter into chemical reactions by borrowing electrons because they have (a) 7 electrons in their outer ring, ( b ) 1 electron in their outer ring, (c) a complete outer ring, ( d ) various combinations of electrons in their outer rings. 9. At room temperature bromine is (a) liquid, ( b ) solid, ( c ) gas, ( d ) none of these. 10. When atoms share electrons, the resulting compound is (a) covalent, ( b ) ionic, ( c) electrolytic, (d) non-electrolytic. 11. If the element chlorine gained one electron during a chemical reaction, it would become a (a ) posi­ tive ion, ( b ) negative ion, ( c) neutral atom, ( d ) none of these.

12. Water is an example of a ( an ) ( a ) ionic compound, ( b ) covalent compound, ( c ) electrolytic compound, ( d ) electrovalent compound. 13. Electrovalent compounds are formed by the transfer of ( a ) neutrons, ( b ) protons, (c ) electrons, (d) all of these.

14. Which of the following form ions and unite to become common table salt? ( a ) sodium and nitro­ gen, ( b ) nitrogen and chlorine, ( c ) nitrogen and helium, ( d ) sodium and chlorine. 15. The chemical breakdown of water, caused by sending an electric current through it, is an example of a ( a ) single replacement reaction, ( b ) double replacement reaction, ( c ) decomposition reac­ tion, (d) combination reaction.

Matching Questions In the space at the left of each item in Column A, place the letter of the term or expression in Column B that is most closely related to that item. Column A

... . .. .

.

·

.

.

. . ..

.

1. 2KCI03 2. Zn + H2SO4

D. ----

Column

ZnS04 + H2

3. S + O2

·

.. . . . . .

4. D.

·

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5. Formation of iOns in solution

·

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6. Anode

D.

. . . .. . .

7. Contains carbon

·

8. C 1 2H22011

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.

. . . . . . . . ·

a . Heat b. Synthesis c. Dissociation d. Decomposition e. Sucrose f. Acetic acid g. Organic compound h . Single replacement i. Hydrogen j. Covalent compound k. Positive electrode I. Negative electrode m . Inorganic

2KCI + 302

. . . . . . . .

B

S02

9. Has only one electron

.

. . . . . . 10. Sharing of electrons

1 70

NAME

______

CLASS

�D �ATE

__ __

__ __ __ __ __ __ __ _

Chapter 1 9

TH E PERIODIC TABLE Scientists have long tried to establish an orderly classification of the elements that would explain and predict their chemical properties. In 1 8 69, a Russian chemist, Dmitri Mendeleyev, arranged the elements in order of their increasing atomic weights. An English scientist, Henry Moseley, used atomic numbers to develop the modern sys­ tem of classifying the elements. This arrange­ ment was the result of Moseley's discovery of the Periodic Law which states that "the prop­ erties of elements are the periodic functions ( regular repetitions ) of their atomic num­ bers ." The atomic number identifies the ele­ ment, since no two elements ever have the same number. The atomic number represents the number of protons in the nucleus or the number of electrons in the rings, since in neutral atoms they are equal. 1. Reading the Periodic Table. The peri­ odic table is used to predict the chemical properties of elements and their activity during chemical reactions. It also aids in the predic­ tion and proper placement of new elements. In the table, the symbol for each element

is placed within a square along with other important information, as indicated below.

Symbol

Na 11

Ato m i c N u m be r Electronic Structure

2-8-1

Key

Example

The elements in the periodic table are arranged horizontally into periods and verti­ cally into groups (families). 2. The Arrangement of Elements Into Peri­ ods. On the periodic table, the periods are numbered from 1 to 7 and extend as horizontal rows across the table. The elements are as­ signed to specific periods according to their atomic numbers, which increase from left to right ( See Table below. ) Elements with atomic numbers 5 8 to 7 1 ( lanthanide series ) and 90 to 1 0 5 ( actinide

Period

First Element

1

Hydrogen

Helium

1

-

2

Lithium

Neon

3

-

10

3

Sodium

Argon

1 1 - 18

4

Potassium

Krypton

1 9 - 36

5

Rubidium

Xenon

37

-

54

6

Cesium

Radon

55

-

86

7

Francium

Actinium

87

-

89

2

23

Atomic We ight

Last Element

Range of Atomic Numbers

1 71

ARRANG EMENT OF ELEMENTS INTO PERIODS

2

7 3 2-1

Li

4 2-2

Be

9 5 2-3

B

11 6 2-4

C

7 2-5

N

14 8 2-6

0

16 9 2-7

F

19 10 2-8

Ne

20

��---�'---�v�---� � ---�v�--�J Metallic or Metallic Non-metallic Inert (gains electrons) (loses electrons) Non-metallic

series ) , are listed separately at the bottom of the table because elements in each of these series have similar properties, and would make the table difficult to read if they were left in the series. Also included on the table, with the ac­ tinide series, are the two latest synthetically produced elements known by publication time. Not all information about these elements is available, but most scientists have identified them as a part of the actinide series. By glancing at the periods, we can predict whether elements will have metallic or non­ metallic properties, or both, and whether a particular element might be inert. By looking at the electron structure we can determine whether the element will have a tendency to lose or gain electrons. Metals tend to lose electrons and non-metals tend to gain elec­ trons. Inert elements are chemically inactive because their outer valence shell is complete or saturated. Careful study of the periods will show that there is a gradual change from strongly metal­ lic elements at the extreme left of a period, to strongly non-metallic elements at the ex­ treme right. The only exception is the last element of each period which is an inert ele­ ment. Elements in the middle of the period may exhibit either metallic or non-metallic properties. These are known as transition ele­ ments. On the chart on page 1 75 , a heavy zigzag line indicates the separation of the metals from the non-metals. 3. Arrangement of Elements Into Groups (Families). The light vertical columns in the periodic table represent the groups or families. Careful study of these groups will show that all members of the same family have the same 1 72

12

number of electrons in their last ring and thus have similar chemical properties. If you learn the general properties of one member of the group, you can predict the properties of the other members. In a family of metals, the most active members are at the bottom of the column. They have the largest atomic numbers and more electron rings. The farther the electrons are from the positive nucleus, the more easily they are lost. In a family of non-metals, the most active members are at the top of the column and have lower atomic numbers. Since these ele­ ments have fewer rings of electrons, the elec­ trons are closer to the positive nucleus. We have learned that opposite charges attract each other, so we can see that the negative electrons are held more strongly by the positive nucleus and will not be easily lost. Families are sometimes given special names as, for example, the Halogen Family or the Family of Inert Gases. They may also be given the name of the first element in the family, as in the Nitrogen Family. (See Table on opposite page. ) 4. Isotopes and Radioisotopes. Isotopes are different forms of the same element. They have the same atomic number but different atomic weights because of a difference in the number of neutrons present in the nucleus of the atom . Since there is no change in the number of electrons, the chemical properties of isotopes are identical to those of the original element. The element hydrogen, for example, has three isotopes known as protium ( ordinary hydro­ gen ) , deuterium, and tritium. Ordinary water is composed of two atoms of protium and one atom of oxygen. Water

, H'

If an isotope is radioactive, it is called a radioisotope. The rate at which a radioactive substance decays is constant and cannot be changed by any physical or chemical method. The rate of decay is different for every element and is called its half-life. The half-life of a radioactive element is the length of time re­ quired for half of the atoms of the original element to disintegrate into simpler atoms. The half-life of U-2 3 8 is about 4 .5 billion years. Thus, in 4. 5 billion years half of the U-2 3 8 will have disintegrated. The final prod­ uct of this radioactive decay is an isotope of lead. By determining the ratio of U-2 3 8 to lead, scientists are able to determine accurately the age of rocks. The half-life of carbon- 1 4, an isotope of carbon, is about 5,760 years. Carbon- 1 4 is used to determine the age of certain fossils.

, H'

Three hydrogen isotopes

composed of two atoms of deuterium and one atom of oxygen is known as heavy water. Heavy water is often used in nuclear reactors to slow down the speed of the neutrons. Natu­ ral uranium is a mixture of two isotopes of uranium, 9 2U23 8 and 92U2 3 5• Both of these isotopes are radioactive ; that is, their nuclei are constantly breaking apart ( disintegrating or decaying ) and releasing energy and, in the process, new simpler elements are formed.

FAMILIES OF ELEMENTS

Period 1 2 3

Alkali Metal Family (IA)

Nitrogen Family Halogen Family (VA) (VIlA)

1 N

1

9

7

23

6 7

80

As

36

53

131

210

209

85 Bi

83

Kr

I

51 Rb

84

1 27

Sb

37

18

35 1 22

K

40 Ar

Br

33

19

10

75

Na

20 Ne

17

39

5

35 CI

15

11

2

31 P

3

4 He

F

7 Li

4

19

14

H

Inert Gases (0)

Xe

At

85

54

133

222

Cs

Rn

55

86 223 Fr

87

1 73

Periodic Table

r--

-

"U 0 ;:

rf

1

IA

1H

3Li

1 1Na

4

19 K

4Be

Mg

39

9

Atomic Number --

�6

�2-4

Carbon

Electron Configuration .-""

2-2 Beryllium

3

2-8- 1 Sodium

Symbol

I IA

7

2- 1 Lithium

3

-c

Atomic Mas s ( Weight) -

1 Hydrogen

2

--1 2

1

i

I

Transition E lements

24

A.

(

GRO U PS

1 2

2

IVB

III B

2-8-2 Magnesium

VB

40 45 8 f 0ea 8C T 21

V

VIB

5

1

�

C r 5Mri 6Fe Vfl B

2

24

23

22

VIII

5

2

6

Cd

2

27

88 HIl 5 388r 39y 89 Zr 1 41N b93 Mer 3Tcr 44Ru 184 6, 590 39 178 a81 a eS33 5 68 3 Lcl ff T W He 60 5 55 J} 6 a 87Fr 88H 89Ac 2-8-8- 1 Potassium

2-8-8-2 Calcium

2-8-9-2 Scandium

2-8- 1 1 -2 Vanadium

2-8-1 0-2 Titanium

2-8- 1 3 - 1 Chromium

2-8-13-2 Manganese

2-8- 1 4-2 Iron

o1

5

37

40

2-8- 1 8-8- 1 Rubidium

2 - 8 - 1 8-8-2 Strontium

2-8- 1 8-9-2 Yttrium

4

42

18

- 1 8 - 1 8 -8 Barium

223

7

73

57

- 1 8 - 1 8-8- 1 Cesium

-32- 1 8-8 -1 Francium

- 1 8 - 1 8-9-2 Lanthanum

2

f3 l H 45 2-8- 1 5 -2 Cobalt

2-8- 1 8 - 1 0-2 2-8- 1 8 - 1 2- 1 2-8- 1 8- 1 3 - 1 2-8- 1 8- 1 4- 1 2-8- 1 8- 1 5- 1 2-8- 1 8- 1 6- 1 Molybdenum Technetium Zirconium Ruthenium Niobium Rhodium

7

6

74

7

7

771r

'

-32-1 8-9-2 Actinium

Lanthanide Series

1 50 40 141 144 e Pr 60Nd 61Pm 6 8m 5 8C 59 1 47

2

Ceriul'l)

Actinide Series 232

�

1 74

23 1

Th 1Pa 90 9 Tbariu m

9

2

- 1 8-32-1 0-2 - 1 8-32- 1 1 -2 - 1 8-32- 1 2-2 - 1 8-32-13-2 - 1 8-32- 14-2 - 1 8-3,- 1 5 -2 Tungsten Osmium Iridium Hafnium Tantalum �henium

227

-32- 1 8-8-2 Radium

9

Protacti nium

U

232

92

Uranium

Praseodymium Neodymium

Prometh i um

Samarium

3 U P ARi C6 m N 95 93 P 9 9 42

237

247

4

Neptunium

P luto"Hlm

Americium

Curium

of the Elements

0

Vi l A

H 2 He 1

GROUPS 1

lilA

5B

IVA

ll

6C

1

2

8 ( f A 14s 2- 4 Carbon

2-3 Boron

\

7

14

N

15

p

3

80

1

6

1

F

9

20

2 Helium

Hydrogen 19

Ne

10

32 3 5 40 S CI 8Ar 16 17 2-6 Oxygen

2-5 Nitrogen

7

13

VI A

VA

4

2-8 Neon

2-7 Fluorine

1

75 80 84 28Ni 2 Cu 30Zn 31Ga 32Ge 3 As 3 Se 35 Br K r 108 1 2 122 128 2 Pd A g 48C d 49In 50Sn 51 Sb 52Te 53 I 5 Xe � 201 204 20 21� 2 0 222. 78 Pt Au 80H g 8 TI 82Pb 83 Bi Po At 86Rn 18

'\

59

11 8

Aluminum 2-8-3

65

64

2-8-4 5111col\

70

Copper

Nickel

2-8-18-3

1

1 06

2-8-1 8-4

Germanium

Gallium

1 15

Sulfur

Argon

Chlorine

9

36

4

3

2-8- 1 8-2 Zinc

2-8-8

2-8-7

2-8-6

3

9

2-S- 1 S- 1

2-8- 1 6-2

Phosphorus 2-8-5

2-8-18-6 Selenium

2- 8 - 1 S-5 Arsenic

2-8- 1 8-7 Brom ine

1 19

2-8-1S-8 Krypton

1

7

4

47

46

2-8- 1 S - 1 8 Palladium

2-8- 1 8- 1 8- 1 2-8- 1 8 - 1 8-2 2-8- 1 S - 1 8-3 2-8- 1 8 - 1 8-4 Indium Silver Cadmium Tin

1 95

31

1 97

7

2 - S - 1 8 - 1 8-5 Antimonv

209

1

79

-8- 1 8 - 1 8-6 2-8- 1 8- 1 8-7 2-8- 1 8- 1 8-8 Tellurium Iodine Xenon 1

I

I

85

84

- 1 8-32- 1 7- 1 - 1 8-32- 1 8- 1 - 1 8-32- 1 8-2 - 1 8-32- 1 8-3 - 1 8-32- 1 8-4 - 1 8-32- 1 8-5 - 1 8-32- 1 8-1 - 1 8-32- 1 8-7 - 1 8-32- 1 8-8 Mercury Lead Platinum Bismuth Polonium Radon Gold Astatine Thallium

52

167 63Eu Gd 65Tb 660 y 67Ho 68Er 69Tm Yb 71 Lu 1

Europium

97

24

Bk

Berke l i u m

1 57

1 59

1 63

1 65

64

Terbium

Dysprosium

Holmium

�huli�'m

Erbium

24 254 25 2 6 25 257 Cf Es 100Fm 101Md 102No 103Lw 9

98

1 75

70

Gadolinium

7

1 73

1 69

3

5

4

99

Einsteinium

Fermium

Mendelevium

Nobelium

YHerbi.um

Rt

?

104

Lawrencium Rutherfordium

Lutetium

Ha

?

1 05

Hahnium

1 75

Elements are often made radioactive arti­ ficially in nuclear reactors by bombarding their nuclei to change their number of neu­ trons. Some of the particles used to bombard the nuclei of elements include electrons, pro­ tons and neutrons. The radiation emitted by radioactive substances consists of three pri­ mary types : alpha particles, beta particles, and gamma rays. ( a ) A lpha Particles ( ex ). These are high­ speed helium nuclei each of which is composed of 2 protons and 2 neutrons. Alpha particles, represented by the symbol 2He 4 , have a positive charge and very little penetrating power. ( b ) Beta Particles ((3). Beta particles are negatively charged electrons with the symbol - 1 eO. They have greater pene­ trating power than alpha particles be­ cause their speed is about equal to the speed of light 1 8 6,000 miles per second. ( c ) Gamma Rays (y). These are very high energy X-rays, having no electrical charge and possessing great penetrat­ ing power. They are extremely danger­ ous, causing burns and mutations. A mutation is a new trait, often harmful to the individual, brought about by damage to the hereditary material of the reproductive cells. Death may result from severe radiation sickness caused by atomic fallout. -

BENEFI CIAL USES OF RADI OISOTOPES

Radioisotope

Use

U-238 to lead

To determine the age of rocks

Carbon-14

To determine the age of fossils; investigation of photosynthesis and respiration

Radioactive iodine

Treating cancer of the thyroid gland

Radioactive cobalt and radium

Treating cancers

1 76

deep-seated

Today, man can change elements into other elements and can produce new elements by changing the number of protons in atomic nuclei. The process of changing elements is called transmutation, and the new elements have atomic numbers that differ from the original element. Elements with atomic num­ bers above 92 (most of the actinide series) were produced in this way. S ELF-DI SCOVERY ACTIVITY Finding Out About Newly Discovered Ele­ ments.

Scientists are making new discoveries about the structure of matter right now while you are studying this Work-a-Text in Physical Science. See what you can find out about discoveries they have made including the synthesis of new elements.

Procedure: Read in newspapers, science magazines and periodicals, and other publications about re­ search into the structure of matter. To find out more information about recently discovered elements, write to : HILAC Lawrence Radiation Laboratory University of California Berkeley, California Use the space below for important notes related to your research.

R EVIEW TESTS Completion Questions For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement. 1. What is the modern periodic table and what is its purpose?

2; Why does the atomic number identify a particular element? . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

3. What is meant by the "Periodic Law?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

4. List four characteristics that can be determined about the element indicated below by examining

the diagram and studying its location in the periodic table : 39

(a) (b)

K

19

(c)

2-8-8-1

(d)

5. How could you determine whether an element had metallic properties by looking only at its .

electronic structure?

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6. Why is the element hydrogen found on both the left and right side of the periodic table? . . . . .

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D � ATE

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1 77

7. Why are the gaseous elements in Group 0 labelled "inert gases?" . . . . . . . . . . . . . . . . . . . . . . . .

8. Metals tend to . . . . . . electrons while non-metals tend to . . . . . . electrons. 9. Why might an element such as carbon form a large number of compounds under the right

conditions? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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10. Why are the elements in the middle of the periodic table referred to as "transition elements?"

11. Why is it advantageous to know to which group or family an element belongs? . . . . . . . . . . . .

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12. The halogen family consists of elements having . . . . electrons in their valence ring. 13. In a family of non-metals, the most active elements are located at . . . . . . . . . . . . . . . . . . . . . . .

14. Why are metals with a larger atomic number more active? . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

15. Uranium is the heaviest natural atom. It has an atomic weight of . . . . . . . . . . . . . . . . and an atomic number of

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16. What is the significance of the zigzag line on the periodic table? . . . . . . . . . . . . . . . . . . . . . . . .

17. What is the meaning of the term "isotope?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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18. Why would ordinary carbon, atomic weight 1 2, have the same chemical properties as carbon- 14?

1 78

NAME����

__ � � � � � � � � � _

CLASS

___

DATE

� � __ � � � � _

19. In the space at the right make a diagram of the deuterium atom. 20. What is the difference between normal and heavy water? . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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21. How is heavy water used? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

22. What is the meaning of the term "radioactive element?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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23. What is meant by the half-life of a radioactive element? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . .. . .. . .. . . . . . . . . .. ..... . ...

24. How are some elements made artificially radioactive?

25. What is the name given to the process that changes one element into another or that creates a new element?

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Multiple-Choice Questions In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question.

1. The atomic number of a natural element can be determined by all of the following except (a) number of electrons only, ( b ) number of neutrons only, ( c ) number of protons only, ( d) number of protons or number of electrons.

2. The atomic weight of an element is the sum of the (a) protons and electrons, and electrons, (c) protons and neutrons, ( d ) protons, neutrons and electrons.

( b ) neutrons

3. In the periodic table, ' elements are arranged according to (a) increasing atomic number, ( b ) decreasing atomic number, (c) increasing atomic activity, (d) decreasing atomic activity. 4. As one goes from left to right in the periodic table, the atomic number, atomic weight and number of valence electrons (a) increase in the first two characteristics only, ( b ) decrease in all three characteristics, (c) decrease in the first two characteristics only, (d) increase in all three characteristics. NAME

_______

CLASS

� DATE

__

_ _ _ _ _ _ _ _

1 79

5. Which of the following elements is on the border line between the metallic and non-metallic elements? ( a ) magnesium, ( b ) chlorine, (c) antimony, (d) iron. 6. In Group IA which would be the more active metal? (a) lithium, ( b ) cesium, (c ) sodium, (d) potassium. 7. All members of the same group or family have the same number of (a) valence electrons, ( b ) total electrons, ( c ) valence as well as total electrons, (d) protons. 8. Members of the Group IA are known as the (a) nitrogen family, ( b ) halogen family, (c) alkali metal family, (d) inert gas family. 9. Which member of the halogen family is the most active element? ( a ) chlorine, ( b ) bromine, ( c ) iodine, (d) fluorine. 10. The nuclei of both an element and its isotope always have the same number of ( a ) electrons, ( b ) neutrons, ( c ) protons, (d) all of these. 11. How many neutrons are found in the nucleus of ordinary hydrogen? (c ) two, (d) three.

( a ) none,

( b ) one,

12. What are the atomic number and the atomic weight of deuterium? (a) 1 and 1 , ( b ) 1 and 2, (c) 1 and 3 , (d) 2 and 2. 13. What is the name of the isotope of hydrogen that has an atomic weight of 3? (a) protium, ( b ) deuterium, ( c ) tritium, (d) all of these. 14. Iodine- 1 3 1 is a radioactive isotope of iodine and has a half-life of 8 days. If 6 grams of this isotope were present at the start, how many grams would be left 1 6 days later? ( a ) 1 2 grams, ( b ) 6 grams, (c ) 3 grams, (d) 1 . 5 grams. 15. What is the most dangerous type of radiation? ( a ) alpha particles, (c ) gamma rays, ( d ) they are all equally dangerous.

( b ) beta particles,

16. A very accurate way of determining the age of rocks is to note the rate at which lead is formed as the result of the radioactive disintegration of ( a ) uranium-238, ( b ) iodine- 1 3 1 , ( c ) carbon1 4, (d) deuterium. 17. Which of the following radioactive isotopes is used to treat cancer of the thyroid gland? ( a ) iodine, ( b ) uranium, ( c ) carbon, (d) hydrogen. 18. An isotope used for investigating photosynthesis and dating fossils is ( a ) carbon-1 4, ( b ) iodine1 3 1 , ( c) uranium-23 8 , (d) deuterium. 19. In order to produce a new element or to change an element into a simpler element, we must change the number of (a ) electrons, ( b ) neutrons, (c) protons, ( d) all of these. 20. Beta particles consist of beams of negatively charged nuclei, (d) none of these.

1 80

NAME

_____ _____

( a ) protons,

CLASS,

( b ) neutrons,

DATE

___

( c ) helium

_ _ _ _ _ _ _ _

Chapter

20

WAT ER Water i s the most abundant compound on earth ; it covers approximately three-quarters of the earth's surface. The earth is saturated by ground water; gaseous water vapor, invisible to the eye, is found in varying amounts in the atmosphere. Water is temporarily locked up in gigantic polar ice caps, rocks and minerals within the earth, and in the tissues of living organisms. Life as we know it would be impossible without water. Water makes up the greatest percentage by weight of protoplasm, the living material of a cell. Water is essential for many of the activities performed by living things such as ( a ) growth, ( b ) digestion, ( c ) absorption, ( d ) circulation and ( e ) excretion. About 60 % of an adult's weight is due to water and about 90% of the liquid part of the blood, called plasma, is com­ posed of water. Water cuts deep into the earth, leaving its imprint as a sculptor leaves his impressions. This life-giving fluid helps to make barren land blossom with vegetation. Our daily weather is affected by large masses of water. Uncontrolled water, such as floods, may destroy life, crops, property, and may wash away valuable topsoil. Most industries are dependent on water. The vast energy of moving water is harnessed to turn the genera­ tors used in the production of electricity. PROP ERTI ES OF WATER 1 . Physical Properties. Pure water is a color­ less, odorless and tasteless liquid. Tap water is impure; its taste comes from dissolved air and minerals. Water possesses some special proper­ ties ; for example, water expands when it freezes, while most other liquids contract. This is because of the shape and arrangement of the water molecules in the ice crystal. Ice, being less dense than water, floats in water. If ice

were denser than water it would sink, causing the water to freeze from the bottom up, killing most of the aquatic life in the process. Water freezes at 0 0 Centigrade ( 0 0 C ) or 3r Fahren­ heit ( 3 2 0 F ) , and boils at 1 00 0 C or 2 1 2 0 F. Water has a very high specific heat; this means that it can absorb or radiate large amounts of heat without greatly changing its own temperature. It is for this reason that large bodies of water require a long time to heat or cool. Thus, as the weather gets colder, a lake, for example, will remain comparatively warm, helping to moderate local weather. Water is often called the universal solvent since it dissolves more substances than nearly any other substance. Digested foods are made soluble in water and are absorbed or taken into the blood and the cells. Many waste products are soluble in water and are removed or ex­ creted from the body in a watery solution. Flowing water erodes our soil and washes away its minerals. However, plants absorb soil minerals which are dissolved in ground water. 2. Chemical Properties. A single water molecule is composed of 2 atoms of hydrogen and 1 atom of oxygen chemically united. Water is a very stable compound. An extremely high temperature, approximately 3000 0 C, is required to decompose it completely. Water often acts as a catalyst. A catalyst is a sub­ stance that speeds up or slows down chemical reactions without itself undergoing any perma­ nent change or being used up during the process. Some substances unite with water in definite proportion by weight to form crystalline com­ pounds called hydrates. Copper sulfate ( CUS04 . 5H20 ) is an example of a hydrate. The dot in the formula indicates that the 5 molecules of water are only loosely attached to the copper sulfate ( CUS04 ) . Hydrated cop­ per sulfate has a blue color. If the water is 1 81

driven off it is called anhydrous copper sulfate and has a white, powdery consistency.

Solutions. A solution is a uniform mixture of a solvent and a solute. The solvent is the sub­ stance doing the dissolving ; the solute is the material being dissolved. Since solutions are mixtures, the solvent and solute do not unite chemically. In addition, a solution has no definite proportion by weight. Water is frequently used as the solvent to make solutions. For example, sugar dissolved in water is a solution in which water is the solvent and sugar is the solute. The sugar is invisible because the sugar molecules are no longer found as crystals but uniformly dis­ tributed in the water. The sugar can be de­ tected by taste and by allowing the water to evaporate. Solutes in a solution will not settle out, nor can they be removed by filtration. The amount of solute and the rate at which it will dissolve in a solvent depends upon : ( a ) the nature of the substance being dissolved ; ( b ) temperature, and ( c ) pressure. Liquids and solids are generally more solu­ ble at higher temperatures ; gases are more soluble at lower temperatures. A gas becomes more soluble as the pressure increases. Car­ bonated drinks are made by dissolving carbon dioxide under increased pressure and decreased temperatures. Removing the bottle cap reduces the pressure, causing the gas to become less soluble and escape, producing bubbles. S ELF- D I SCOVERY ACTIVITY Investigating the Effect of Temperature on the Solubility of Carbon Dioxide.

Materials: Two bottles of carbonated beverage, such as 7-Up, Coca Cola, or Pepsi Cola, a bottle opener, refrigerator, warm tap water.

Procedure: Place one bottle unopened in the refrigerator until it is cold. Place the other bottle in warm 1 82

tap water not exceeding 1 20 ° F. Wait five minutes for the bottle in warm water to heat up. Then, carefully remove the caps from both bottles. What do you observe?

Observations:

Conclusions:

EFFECT OF TEMPERATUR E O N SOLUBILITY ... .... ...:: � .... co:

0

E

0 CI

... .... co:

1 00 90 80

en �

50

!:

40

...:: co: c::o

.... ::::; ;; => -' >-

0 en

;1/

60

30 20 10 0

�

� � �� V

/ o

/

II

/

'j

� §

70

'� �f � I/

f

SOOIUM CHLORIO - NaCI

�

t'o

so. �� � � ...--"

tA SU\:H;t� -

1 0 20 30 40 50

60

V.

70 80 90 1 00

TEMPERATURE _0 C

Careful examination of the graph shows that most solids become more soluble in water as the temperature increases. At 0° C, the freezing point of water, 1 00 m!. of water will dissolve only about 1 3 grams of potassium nitrate ( KNO:l ) , whereas the same quantity of water can dissolve 1 00 grams of this compound at about 5 5 ° C. We can increase the rate at which a solid ( solute ) dissolves in a liquid (solvent ) by ( 1 ) pulverizing or grinding the solid, ( 2 ) stirring or mixing the solution, and ( 3 ) increasing the temperature of the solvent. An increase in tem­ perature thus increases both the solubility of

most solutes and the rate at which the solute will dissolve. Solutes affect the freezing and boiling point of the solvent. They raise the boiling point and lower the freezing point. In winter, antifreeze is added to water in an automobile radiator to prevent freezing by lowering the freezing point. In summer, antifreeze may be added to raise the boiling point. SELF-DISCOVERY ACTIVITY Exploring the Effect of Particle Size, Stirring and Heating on the Rate at Which a Given Solute Will Dissolve.

Materials: Five test tubes, copper sulfate ( euSO 4 ) crystals, mortar and pestle, bunsen burner.

Procedure: Fill each of the 5 test tubes one-half full of water. Select 5 crystals of euso 4 of about the same size. ( a ) Drop one crystal into a test tube and allow the tube to stand. ( b ) Drop one crystal into a test tube and heat the tube over the flame of a bun­ sen burner.

Observation: How did heat affect the rate of solubility?

( c ) Drop one crystal of euso 4 into a test tube and shake the tube vigorously while holding your thumb over the mouth of the tube.

Observation: How did pulverizing affect the rate of solubility?

. . .. . . . .. . . . . . . . . . . . .. . . . . . . .

.

( e ) Pulverize one crystal of euso 4 and drop the material into a test tube. Shake the tube vigorously.

Observation: How did shaking the pulverized euso 4 affect the rate of solubility? . . . . . . . . . . . . .

.

Conclusions: Did your investigation support the statement of the authors about the effects of particle size, stirring, or heating on a solid solute?

Types of Solutions. Solutions may be classified by comparing the amount of solute with re­ spect to a given amount of solvent present. 1. Dilute Solution. A dilute solution con­ tains a large amount of solvent compared to a relatively small amount of solute.

How did shaking affect the rate of solubility?

2. Concentrated Solution. A concentrated solution contains a comparatively large amount of solute dissolved in a small amount of sol­ vent. A concentrated hydrochloric acid solu­ tion ( Hel ) contains a relatively large amount of hydrochloric acid in a comparatively small amount of water.

( d) Drop one crystal of pulverized euso 4 into a test tube and allow the tube to stand.

3. Saturated Solution. A saturated solution is one in which the solvent has dissolved all the solute it can dissolve at a given temperature and pressure. 4. Supersaturated Solution. A supersatu­ rated solution contains more dissolved solute

Observation:

183

than it could normally hold at a given tempera­ ture and pressure. Since more solute can be dissolved at higher temperatures, lowering the temperature of the solution will cause some of the dissolved ma­ terial to settle out. Some substances, such as photographic hypo ( sodium thiosulfate ) , how­ ever, will not settle out if the solution is cooled slowly, thus making a supersaturated solution. Supersaturated solutions are not very stable. Adding a single crystal of solute or shaking the container will cause the excess dissolved solute to settle out, leaving a saturated solution behind. This intended agitation or disturbance is called seeding.

Suspensions. A suspension is a non-uniform mixture of tiny, insoluble solid particles dis­ tributed in a liquid or a gas. The particles eventually settle out on standing. The sus­ pended particles are visible and can be re­ moved by ordinary filtration. Muddy water, oil base paints, and dust in the air are some com­ mon examples of suspensions . Colloids. Colloids ( colloidal dispersions ) are special kinds of suspensions. They are com­ posed of particles intermediate in size between those of a solution and a suspension. Colloidal particles are thus larger than the molecules found in a solution but smaller than the tiny visible particles found in a true suspension. The particles in a colloidal suspension are so small they never settle out. This results from the constant bombardment of the particles by the vibrating molecules of the suspending medium. The erratic, zigzag motion of the particles is called Brownian movement. The haphazard movement of dust particles visible in a strong beam of light also illustrates Brownian move­ ment. Some examples of colloids include : milk, smoke, jello, and protoplasm - the liv­ ing material of a cell . S ELF-DI SCOVERY ACTIVITY I nvestigating the Differences Between a Solu­ tion and a Suspension. 1 84

Materials: Three 1 00 ml. beakers, graduated cylinder, stirring rod, tablespoon, water, sugar, soil, alcohol, paper toweling or filter paper, funnel.

Procedures and Observations: ( a ) Place 7 5 ml. of water in beakers A, B, and C. Place a tablespoonful of sugar in A, a tablespoonful of soil in B, and a tablespoonful of alcohol in C and thor­ oughly stir each. A

B

c

( b ) Describe the appearance of the ma­ terial in each of the beakers, including presence or absence of visible particles. H 2 0 + sugar: . . . . . . . . . . . . . . . . .

.

H 2 0 + soil : . . . . . . . . . . . . . . . . . . . H 2 0 + alcohol : . . . . . . . . . . . . . . . . ( c ) Allow the samples to stand for about 20 minutes. In which sample or samples did the solute settle out? . . . . . . .

( d ) After thoroughly remixing the samples, try to separate the solutes by filtration. Which solutes were removed by this process? . . . . . . . . . . . . . . . . . . . . . .

.

Conclusions: ( a ) Tell whether the following samples were solutions or suspensions :

H 2 0 + sugar: . . . . . . . . . . . . . . . . . . H 2 0 + soil : . . . . . . . . . . . . . . . . . . . H 2 ° + alcohol : . . . . . . . . . . . . . . .

.

( b ) What properties were illustrated in this experiment that enabled you to differ­ entiate between solutions and suspen­ . Slons ?. . . . . . . . . . . . . . . . . . . . . . . . .

5. Filtration. Water is allowed to pass through a filter composed of sand and gravel to remove suspended solids. Charcoal is also used to remove bad odors and colors. -

-

--

-.----��

--

--

--

�--

.

Purifica tion of water by filtra tion.

Water Purification. Water found in nature usually contains impurities. Some impurities, when present in large quantities, may give water a disagreeable taste or odor, or make it unsafe for drinking. Water may be made fit to drink (potable) by the following methods : 1. Boiling. If water is boiled for a sufficient length of time, most harmful germs will be destroyed.

2. Distillation. This method consists of boil­ ing and evaporating a fluid, in this case, water, and condensing the water vapor to remove im­ purities. Distilled water is often used to prepare water solutions of medicines. The preceding two methods are only suit­ able in purifying small quantities of water. Water purification on a large scale uses the following processes to bring s afe drinking water to communities : 3. Sedimentation. In this process the water is collected in reservoirs or settling basins and the large solid particles settle to the bottom. 4. Coagulation. The addition of chemicals, such as alum or lime, will cause fine particles to j oin together and clump or coagulate in a jellylike mass which settles to the bottom.

6. Aeration. Filtered water is usually sprayed into the air (aeration) to help remove odors, kill bacteria and eliminate gases that give water a bad taste. 7. Chlorination. Chlorine compounds are added to water to kill harmful bacteria. Chlo­ rine is added to the water in swimming pools as well as to drinking water.

Hard and Soft Water. Water for home use may be classified as hard water or soft water, de­ pending on the type and amount of minerals it contains. 1. Hard Water. Hard water contains the ions of calcium, magnesium or iron. These ions interfere with the ability of soap to form suds. As a result scum forms, often visible as a ring in the bathtub. Boilers and water pipes are often clogged by deposits of calcium carbonate. Temporary hard water contains calcium or magnesium salts in solution which can be re­ moved by boiling. Permanent hard water contains calcium or magnesium salts ( calcium or magnesium sul­ fates or chlorides ) which cannot be removed by boiling. 2. Soft Water. Soft water contains very little dissolved minerals. Water softeners are often added to water used for washing clothes. Some commercial water softeners contain a sub1 85

stance called "zeolite," which removes many dissolved minerals. Certain resins, called "ion­ exchange resins" are also used to remove the minerals which cause hard water.

A New Kind of Water? In the mid- 1 9 60's, Russian scientists announced that they had dis­ covered a new and different form of water. Found in tiny capillary tubes, the new "water" had the consistency of grease, and did not boil until a temperature of 3 00 0 C. was reached. Its freezing point was below - 1 0 0 C. After preparing some of the mysterious m aterial, U.S. scientists proposed that the greasy substance is a form of water in which the molecules form a chain or polymer. Thus, the name "polywater" was given the unusual substance. Even today, scientists are still studying polywater to find out more about its unique properties. Water Pollution. Approximately three-quarters of the earth's surface is covered with water, and about 97 % of this water is salt water, un­ suitable for human consumption. Much of the remaining 3 % of the water is unavailable since it is deep in the ground or locked up in polar ice caps. An increasing population and tremen­ dous industrial growth are steadily demanding more of the limited fresh water supply. Indus­ trial and community wastes are dumped into streams, lakes and rivers, and are greatly re­ ducing the available supply of fresh water and destroying much of the aquatic life. Because of these factors and the general scarcity of water in many areas of the world, the lack of water is a major concern. The prob­ lem is so widespread that in 1 965 the United Nations sponsored an international organiza­ tion to help solve this problem. A huge step forward is the erection of desalinization plants to make fresh water from sea water on a large economical, commercial basis. S ELF- D I SCOVERY ACTIVITY Discovering Some Materials Which Can Be Used to Soften Hard Water.

1 86

Materials: Hard water ( containing calcium sulfate ) , soap solution, 3 test tubes, 3 corks, graduated cylinder, washing soda, borax.

Procedure: To 3 test tubes add 1 0 m!. or about one-third of a test tube of hard water. To each test tube add the following : ( a ) Test tube 1 . Three drops of soap solu­ tion. Shake the tube. ( b ) Test tube 2. A small piece of washing soda, 3 drops of soap solution. Shake the tube. ( c ) Test tube 3 . A pinch of borax, 3 drops of soap solution. Shake the tube.

Observations: Describe the amount of suds formed in each tube after shaking. Test tube 1 : Test tube 2 : Test tube 3 :

Conclusions: What conclusions would you draw from the evidence resulting from this experiment? . . . .

R EVIEW TESTS Completion Questions For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement. .

1. About

.

.

% of an adult's weight is due to water and about 90% of his . . . . . . . . . is com-

posed of water. 2. Name five life functions common to all living things which are in part dependent upon water.

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4. Why does water play an important role in the processes of digestion and absorption? . . . . . . . .

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3. Explain why large bodies of water affect local weather. .

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6. Water is a chemical

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7. Water often acts as a catalyst in a chemical reaction. What is the meaning of the term "catalyst?" .

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8. C US04 ' 5H20 is an example of a hydrate.

(a) What is the meaning of the term "hydrate?"

( b ) What does the dot in the formula C US04 ' 5H20 mean? . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

�A�E

__ __ __ __ __ __ __ __ __ __ __ __ __ __ __

CLASS,

� DATE,

_ _

__ __ __ __ __ __ __ _

187

9. Complete the following chart:

Suspension

Solution

Colloid

Particle size (visible ­ invisible? ) Effect of filtration Effect of standing 10. Ten grams of salt were added to a small volume of water. The mixture was then heated. .

(a) Name the solute.

( b ) Name the solvent.

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1 88

NAME

______

CLASS

DATE

_____

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Multiple-Choice Questions In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question.

( b ) 90% , (e) 1 5 % ,

(a) 75 % ,

1. The earth's surface is covered by approximately water.

(d) 60%

2. Water takes a long time to heat and to cool because of its (a) molecular shape, ( b ) impurities, ( c ) density, (d) high specific heat. 3. Water, upon freezing, (a) contracts, ( b ) expands, (e) chemically changes, (d) remains the same.

4. The freezing point of water is (a ) 1 00 0 C, ( b ) 00 P,

( c ) 00 C,

(d) 320 C.

( a) excretion,

5. Water acts as a solvent to eliminate wastes in the process of (c) reproduction, (d) secretion.

( b ) digestion,

6. When water is driven off from copper sulfate ( CUS04 . 5H20) , the remaining product is called

(a) hydrated, ( b ) dry, (c) carbonated, (d) anhydrous 7.-11. The following questions relate to the graph : 7. Which letter represents the compound with the highest solubility at 30° C? ( a ) B, ( b ) C, (c) A, (d) E. 8. As the temperature increased, the solubility of compound C ( a ) decreased, ( b ) in­ creased, ( e ) remained the same, (d) im­ possible to determine from the graph. 9. How many grams of compound C will be needed to saturate 1 00 ml. of water at 500 C? ( a ) 20, ( b ) 80, ( c ) 40, ( d) 10 . 10. Which letter represents the compound least soluble at 7 3 0 C? ( a ) B, ( b ) D, (c) E, (d) C. 11. Which letter represents the compound whose solubility increases most slightly as the temperature increases? ( a ) B, ( b ) E, (e) A, (d) C. NAME

____

copper sulfate. EFFECT OF TEMPERATURE ON SOLUBILITY

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1 89

12. A dilute solution of HCI would contain a great deal of (a) HCI, ( b ) water, (c) CI, (d) none of these. 13. Which term would you not associate with solutions? (a) solute, ( b ) solvent, ( c ) sedimentation, (d) uniform mixture. 14. Protoplasm is an example of a ( a ) solution,

( b ) suspension,

(c) colloid, (d) none of these.

15. The constant movement of colloidal particles due to molecular bombardment is called (a) Brown­ ian movement, ( b ) coagulation, (c) vibration, (d) displacement.

Matching Questions In the space at the left of each item in Column A, place the letter of the term or expression in Column B that is most closely related to that item. Column

Column A

a. b. c. d.

1. Addition of alum or lime to water

2. Often found in hard water 3. Spraying water into the air to remove bacteria and odors

e.

4. Zeolite and ion exchange resins

f.

5. Forms many suds with little soap g.

6. Colorless, odorless, tasteless

h.

7. Chemical added to water to kill bacteria i.

8. Makes water unfit for human consumption and destroys aquatic life

j.

k. [.

9. Chalk particles in water

m.

10. Milk

1 90

NAME

______

CLASS,

Soft water Tap water Fluorine Coagulation Pure water Calcium or magnesium sulfates or chlorides Aeration Commercial water softeners Chlorine Filtration Pollution Colloid SuspensIOn

D � ATE

__ __ __

B

_ __ __ __ __ __ __ __

Chapter

21

AC I DS, BAS ES A N D SA LTS If you had studied chemistry 20 years ago, your teacher would h ave begun with a discus­ sion of acids, bases, and salts. This emphasis would have continued during much of the year because the reactions between acids and bases to form a salt were considered to be the pri­ mary chemical actions in m atter. Today, the emphasis has changed to studying the chemical properties of individual elements. However, an understanding of these chemical compounds still has an important place in the chemistry laboratory. In order to know what an acid, a base, or a salt is, it is important to review the meaning of ionization, which we studied earlier. Ionization is the process by which the molecules of certain electrovalent compounds come apart ( dissoci­ ate) in solution. The resulting free, charged particles, which may be atoms or radicals, are called ions. Acids are hydrogen-containing compounds whose water solutions contain positive hydro­ gen ions (H + ) . Bases or alkalis are compounds whose water solutions form negative hydroxyl ions ( OH-) . Salts are crystalline substances composed of positive and negative ions. In order to detect the presence of an acid or a base, chemical indicators are used. These chemicals change color when added to acid and basic ( alkali) solutions . Common indi­ cators used in the laboratory are blue and pink. litmus paper ( derived from a plant extract ) and phenolphthalein. Acids turn blue litmus paper pink, and bases turn pink litmus paper blue. Phenolphthalein is colorless in an acid solution and reddish pink when a base is present. The pH scale is a numerical scale used to measure the strength of acids and bases. The p stands for potential energy of electric charges and the H stands for the hydrogen ion. If a solution has a pH of 7 , it is neutral, meaning that it is neither an acid nor a base.

If the pH is below 7, the solution is an acid.

The lower the number below 7 , the stronger the acid. If the pH is above 7, the solution is a base (alkali). The higher the number above 7, the stronger the alkali. increasing acidity

increasing alkalinity

pH 1 ··""'---

pH 7 ----., pH 1 4 neutral ACIDS

Acids, as we have stated, are hydrogen­ containing compounds whose water solution contains positive hydrogen ions ( H + ) . The greater the concentration of hydrogen ions, the stronger the acid. HCI

H+

hydrochloric acid

+ CI­

hydrogen chloride ion ion

The hydrogen ion is usually written in the form of H + for the sake of simplicity. It is more accurate scientifically, however, to write it in the form of the hydronium ion ( H .)., O + ) , since these are the ions actually formed in a water solution, as seen below:

hydro­ chloric acid

water

hydro­ nium ion

chloride ion

1. The Properties of Acids. The properties of acids result from the formation of hydro­ nium ions in solution. Sulfuric, hydrochloric and nitric acids are strong acids since they form many hydronium ions in solution. Acids have the following general properties : ( a ) Form hydronium ions ( H il 0 -t- ) in . solution. ( b ) Taste sour like a lemon. ( c ) Turn blue litmus paper pink and pink phenolphthalein solution colorless.

1 91

( d ) Have a pH below 7 . ( e ) Are caustic ; that is, strong acids des­ troy organic tissue and many metals. (f) Neutralize bases forming a salt and water : HCl hydro­ chloric acid

+ NaOH

--_I

NaCl + H20

sodium chloride ( a salt)

sodium hydroxide ( a base )

water

( g ) Some acids react with metals, forming a salt and releasing hydrogen :

hydrochloric acid

+

Zn

zinc ( a metal )

ZnClz +

•

H2

t

zinc hydrogen chloride gas ( a salt )

(Single Replacement) 2. Common Industrial and Laboratory Acids. The following acids are important III both industry and research : ( a ) Sulfuric acid (H2SO,,). This acid is used in a large number of industrial processes. Some of these include the manufacture of drugs, dyes, rubber, storage batteries, fertilizers, and of other acids. It is a strong dehydrating agent (removes water ) . ( b ) Hydrochloric acid (Hel). An impure form of this acid, muriatic acid, is used to clean metals in a process called pickling and is used in the manufac­ ture of soldering acid. Hydrochloric acid is also used in the manufacture of glue, sugar, gelatin, and other acids. ( c ) Nitric acid (HNOa). Nitric acid is

Common Household Acids Citric acid Acetic acid Acetyl salicylic acid Boric acid Carbonic acid

1 92

BAS ES

Bases or alkalis are compounds which, when in water solution, form negative hydroxyl ions ( OH- ) . NaOH

(Double Replacement)

2HCl

used to manufacture explosives, photo­ graphic film, drugs, plastics and ferti­ lizers.

-

sodium hydroxide ( a base )

Na +

sodium ion

OH­

+

hydroxyl ion or hydroxide

In all bases, except ammonium hydroxide, the hydroxyl ion is chemically united with a metal or metallic radical. The properties of bases ( alkalis ) result from the formation of hydroxyl ions in solu­ tion. Sodium hydroxide and potassium hydrox­ ide are strong bases since they form many hydroxyl ions in solution.

The Properties of Bases. ( a ) Form hydroxyl ions ( OR-) in solu­ tion. ( b ) All ( except ammonium hydrpxide ) contain metallic ions or metallic radi­ cal ions. ( c ) Their water solutions have a bitter taste. ( d ) Their water solutions are slippery to the touch. e) Turn pink litmus paper blue and color­ e less phenolphthalein red or pink. (f) Strong bases are caustic to the skin and to many natural fibers such as wool. ( g ) Neutralize acids, forming a salt and water :

Source or Use citrus fruits vinegar aspirin

eye washes

soda pop

sodium hydroxide ( a base )

sulfuric acid

sodium sulfate ( a salt)

water

(Double Replacement)

Note: Water may be written as H20 or HOH.

Some Important Bases

HN03 + NaOH ( acid) (base )

Uses

Sodium hydroxide

Manufacture of hard

(NaOH) (lye or caustic soda)

(KOH)

(Ca(OHh)

troleum, lye, and many

2. Reaction Between an Active Metal and an Acid. In order for this reaction to take place, the metal must be above hydrogen in the activity (electromotive ) series of metals. When the metal is above hydrogen, it is more active than hydrogen and thus will replace all ( or part ) of the hydrogen in the acid.

Manufacture

of soft

soap, greases, and potas­ Manufacture of mor­ tar, plaster, and lime­ water

Ammonium

Manufacture of house­

hydroxide

hold ammonia water, fertilizers, and explosives

(NH40H)

sodium nitrate

(Double Replacement)

sium salts Calcium hydroxide

=

NaN03 + ( a salt )

soap, paper, rayon, pe­ sodium salts

Potassium hydroxide

NaNOa

-

H2S04 + Zn - ZnS04 + H2 t ( acid) ( active ( a salt ) ( hydrogen ) metal ) ZnS04

=

zinc sulfate

(Single Replacement) SALTS

Salts, as you have learned, are crystalline substances composed of positive and negative ions. These ions are usually positive metal ions from a base and negative non-metallic ions from an acid. Salts may also be defined as the crystalline products formed as the result of a neutralization reaction of an acid and a base. Ordinary table salt is chiefly the salt sodium chloride ( NaCl ) . Sodium chloride is only one example of the many salts that exist. Salts may be prepared as a result of a number of chemical reactions, some of which are : 1 . Neutralization. As you have learned, a solution is neutral when it possesses neither acid nor basic properties and has a pH of 7 . Neutralization is the reaction between an acid and a base to produce water and a salt. The resulting solution is said to be neutral when the number of hydrogen ions equals the number of hydroxyl ions. Here are two examples of neutralization reactions :

NaCl + HCI + NaOH ( a salt ) ( acid) ( base ) (Double Replacement) -

3. Direct Combination of a Metal and a Non-metal. An example of this method of salt production is the following : CuCb ( a salt)

Cb Cu + ( non-metal ) ( metal) CuCb

=

copper chloride

(Chemical Combination (Synthesis))

Some Important Salts

Uses

Sodium chloride (NaCI)

Table salt, manufacture of other sodium salts, and hydrochloric acid, essential for life.

Sodium carbonate (Na2C03)

Manufacture of glass and washing powders.

Sodium bicarbonate (NaHCOa)

Manufacture of baking soda, used in carbon dioxide fire extinguishers.

Sodium nitrate (NaNOa)

Manufacture of fertilizers and explosives.

Magnesium sulfate (MgS04)

A laxative salts ) .

Copper sulfate (CUS04)

Used in copper plating, and manufacture of fungicides.

( Epsom

1 93

4. Chemical Reaction Between a Base and a Salt. This reaction results in the formation of a different base and a salt.

Boiled, distilled water

2NaOH + CUS04 - C U ( OH ) 2 + Na2 S04 ( base ) ( a salt) (base ) ( a salt ) CUS04 Na2S04

= =

Contents

Test Tube

copper sulfate sodium sulfate

2

Unsweetened lemon juice

3

H20 plus 5 drops of vinegar

4

H20 plus 5 drops of Ca(OHh solution

5

H20 plus 5 drops of NH40H solution

(Double Replacement)

( b ) Place a single drop of each of the above solutions on the tip of your tongue and record the re� suIts in the chart that fol­ lows.

S ELF-DISCOVERY ACTIVITY

Investigating Some Properties of Acids and Bases.

Materials:

CAUTION: Never taste or swallow any solution unless directed to do so by your in­ structor.

Distilled water, unsweetened lemon juice, vinegar, calcium hydroxide solution Ca ( OH h, ammonium hydroxide solution ( NH40H), five test tubes, test tube rack and stirring rod.

( c ) Test each of these solutions with blue and pink litmus paper and a colorless phenolphthalein solution and record the resulting colors in the following chart.

Procedure: ( a ) Number the 5 test tubes ; fill them half full of the following materials and place them in a test tube rack :

Observations: SOME PROPERTIES OF ACIDS AN D BASES

Contents

Taste

Pink litmus

Phenolphthalein Solution

Blue litmus

Distilled water Lemon juice Vinegar solution Ca ( OHh solution NH40H solution

1 94

NAME'

_____ _______

CLASS,

�DATE,

_ _

_ _______

R EVIEW T ESTS Completion Questions For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement. �_

.

.

1. What is an acid? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2. What is the meaning of the term "ionization?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

3. What determines the strength of an acid? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4. Strong acids and bases are caustic when handled improperly. What is the meaning of the scientific term "caustic?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . .

5. A solution would be neutral if the pH was . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. What is the meaning of the term "neutralization?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7. Write the equation which represents the neutralization reaction between sodium hydroxide and hydrochloric acid and give the chemical names of the two resulting products.

( a ) Equation : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ( b ) Name of products : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8. The following solutions were tested with blue and red litmus paper and colorless phenolphthalein.

Fill in the blanks in the following chart with the resulting colors. Indicator

Lye

Vinegar

Potassium hydroxide

Lemon juice

Pink litmus Blue litmus Phenolphthalein

NAME

_______

CLASS

___

DATE

_ _ _ _ _ _ _ _

1 95

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9. What is muriatic acid? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10. Write the equation showing the reaction between hydrochloric acid and zinc and name the resulting products.

(a) Equation :

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( b ) Name of products : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11. A base, sometimes referred to as an alkali, is a solution containing . . . . . . . . . . . . . . . . . . . ions. .

12. When will a solution be neutral? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13. Write the formula for each of the following :

(a) hydrogen ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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( b ) hydronium ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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(c) hydroxyl ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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14. Below is a list of common household items. Name the major chemical component and tell whether that chemical is an acid or a base. Household Item

Acid or Base

Major Chemical

Hard soap Vinegar Citrus fruit Lye Ammonia water 15. Hydroxyl ions have a . . . . . . . . . . . electrical charge, whereas hydrogen ions have a . . . . . . . . . .

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16. What is a salt? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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17. A salt is formed by the chemical combination of a metal and a(an) . . . . . . . . . . . . . . . . . . . . . . . 18. Name the salt in the following equation : Cu + Cb

1 96

NAME

--_.

_______ ___

CLASS,

CuCl2

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19. Give one important use for each of the following salts :

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( b ) Na2C03 : . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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20. If a student spilled some hydrochloric acid on his hand, and rushed to the sink to wash off the acid,

(a) Which of the following substances would be best to neutralize the effects of the hydrochloric acid - sodium hydroxide or sodium bicarbonate? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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( b ) Why did you select this choice? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Mu ltiple-Choice Questions In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question. 1. Which of the following are charged atoms or radicals? (a) hydronium ions, ( b ) hydrogen ions, (c) hydroxyl ions, ( d ) all of these. 2. The actual ions formed by acids in a water solution are called (a) hydronium ions, ( b ) hydrogen ions, ( c ) hydroxyl ions, ( d ) chloride ions. 3. The pH number of a substance is the measurement of (a) acidity only, ( c ) acidity and basicity, (d) neither acidity nor basicity.

( b ) basicity only,

4. How many of these pH numbers signify basic properties for a substance - 1 , 2, 7, 1 3 ? (a) one, ( b ) two, (c ) three, (d) four.

5. Pink litmus paper will, in the presence of a base, (a) turn black, ( b ) turn colorless, (c) turn blue, (d) remain pink.

6. The chemical formula for hydrochloric acid is ( a ) H2S04, ( b ) HCl, ( c ) HN03, (d) H2C03• 7. Which of the following industrial acids is used in storage batteries and the manufacture of other acids, drugs and dyes? ( a ) sulfuric acid, ( b ) carbonic acid, ( c ) hydrochloric acid, (d) nitric acid. S. Which industrial acid is used to manufacture explosives, photographic film, plastics and fertilizers?

(a) sulfuric acid, ( b ) carbonic acid, ( c ) hydrochloric acid, (d) nitric acid.

9. Metals are quickly attacked by (a) strong bases, ( b ) strong acids, ( c) weak bases, (d) weak acids . 10. In all bases, except ammonium hydroxide, the hydroxyl ion is united to a ( an ) ( b ) i nert gas, (c ) halogen, (d) metal .

(a) non-metal,

11. Bromothymol blue is a chemical which turns yellow in an acid. This chemical could be used as a ( an ) ( a ) alkali, ( b ) acid, ( c ) indicator, (d) laxative. 1 97

12. Potassium nitrate ( KN03) is a salt which would be formed when potassium hydroxide (KOH) is used to neutralize the effects of (a) hydrochloric acid, ( b ) nitric oxide, (c) sulfuric acid, (d) nitric acid. 13. In order for a metal to replace the hydrogen in an acid, its location in the activity series of metals must be (a) above hydrogen, ( b ) below hydrogen, (c) very close to hydrogen, (d) it makes no difference. 14. The chemical formula for sodium bicarbonate is (d) NaCl.

(a) Na2COS,

( b ) NaHC03,

(c) N�SOt,

15. The salt that is used in the manufacture of fungicides is (a) magnesium sulfate, ( b ) sodium chloride, ( c ) sodium carbonate, (d) copper sulfate.

Matching Questions In the space at the left of each item in Column A, place the letter of the term or expression in Column B that is most closely related to that item. Column

Column A

1. Turns pink or red in a base

a. Blue litmus b. Strong acid c. Aspirin d. Acids e. NaOH f. Phenolphthalein g. Pickling metals h . Red litmus i. Neutralization j . Hydroxyl ion k. Eye wash t. Calcium hydroxide m. Bases

2. Muriatic acid 3 . 0H4. Used to make mortar 5. Acetyl salicylic acid 6. Turns pink in an acid 7. Sour taste 8. Lye 9. Large concentration of hydronium ions 10. HCl + NaOH

1 98

NAME

-

B

NaCI + HOH

______

CLASS,

___

DATE

_ _ _ _ _ _ _

Chapter

22

I RON A N D STEEL Prehistoric man originally used sharpened stones as tools and weapons. Then, about 7000 years ago, he discovered copper and used this metal as a substitute for stone. Man entered the Bronze Age after he discovered how to make bronze by melting together copper and tin. Although stronger than copper, bronze was still a soft metal. The Age of Iron began after man learned how to extract the metal from iron-rich min­ erals by heating them to a sufficiently high temperature in the presence of charcoal. The oldest known iron objects are iron beads dis­ covered in an Egyptian cemetery and dating back to about 4000 B.C. IRON

Iron was the first truly strong metal avail­ able for making tools, weapons and utensils. Today, iron, and the steel manufactured from it, are the very backbone of the economy of many nations. Buildings, machinery, auto­ mobiles, ships , trucks, household appliances, weapons, and thousands of other objects de­ pend on the production of iron and steel. 1. The Occurrence of Iron. Iron is fourth in abundance among all the known elements in the earth's crust. It is the second most common metal, being surpassed only by alu­ minum. Since iron is a fairly active metal, it is rarely found in the free or chemically un­ combined state, except in meteorites. Metals found in the free state are native metals. Compounds of iron are abundant; they are found in most plants and animals. Hemo­ globin, for example, is an iron-rich compound found in our red blood cells. It gives blood its color and enables blood cells to carry vital oxygen to all parts of the body. Many of the foods we eat, such as liver and green leafy vegetables, are rich in iron compounds. An ore is a mineral compound from which

a metal or non-metal can be extracted prof­ itably in commercial quantities. Some of the major iron ores are hematite (Fe203), limonite (2Fe203 ' 3H20), and magnetite (Fe304)' Hematite is the best and most impor­ tant of the iron ores. It was once found in great quantities in the Mesabi Range, a huge open­ pit iron ore mine located in Minnesota, near Lake Superior. The low-grade mixture of magnetite and hematite ores remaining in the Mesabi Range is known as taconite. It contains only 2 5 % iron and was once considered unusable because of the high cost of extracting the iron. This are is now concentrated and pressed into pellet form for use in the production of iron.

2. The Metallurgy of Iron and the Use of the Blast Furnace. Metallurgy is the science of separating a metal from its ore (extraction) and removing unwanted impurities ( refining ) . Since iron ores are primarily found as oxides of iron, the major problem is to remove the oxygen, thus freeing the iron. Removing the oxygen from the iron ore at high temperatures is called reduction. The process takes place in blast furnaces. The blast furnace is a huge, round furnace, from 1 00 to 200 feet high and 20 to 30 feet in diameter. Its steel walls are lined with firebrick which withstands high temperatures. The raw materials which make up the charge of the furnace are brought to the top of the furnace by rail cars called skip cars. The charge is dumped into the top through trapdoors where it falls onto structures called bells which prevent loss of furnace heat. Standing next to the blast furnace is a row of three or four cylindrical stoves which pre­ heat the air that enters the furnace. This pre­ heated air passes into a huge pipe called the bustle pipe which circles the base of the furnace. Smaller pipes, called tuyeres, permit 1 99

blasts of hot air to enter the blast furnace. This hot air is necessary to maintain the proper temperature required to operate the furnace. Waste gases are removed through large pipes at the top of the furnace. This waste gas is carried to the stoves and is used as fuel to preheat the air. Molten iron and wastes collect in a huge basin-like structure called a hearth, at the base of the furnace. 3. The Charge of the Blast Furnace. The raw material or the charge of the furnace consists of a mixture of ( a ) iron ore, ( b ) coke, ( c ) limestone, added in alternate layers .

( a ) Iron ore. Hematite, magnetite and taconite are the primary ores from which the iron is to be extracted. Two tons of iron ore are needed to produce one ton of iron. ( b ) Coke. Coke, a material rich in carbon, is produced by heating soft ( bitumin­ ous ) coal in the absence of air. Coke serves two important functions in the blast furnace : (1) HEAT. As coke is burned in the blast furnace, it supplies sufficient heat to start the chemical reactions and to melt the iron at a temperature of about 3 000° F. (2) RE­ DUCING AGENT. A reducing agent is a substance that removes oxygen from a compound. The carbon in coke unites with the oxygen in the iron ore, re­ placing the iron in the process. The result is iron metal and carbon monox­ ide, as shown in the following equation : Fe203 + 3 C hematite carbon

-

D.

2Fe + iron

The molten liquid iron drips down and col­ lects in the hearth. ( c ) Limestone. Limestone ( CaC03 ) is used to remove impurities, chiefly sil­ ica ( sand ) , from iron. It forms a waste product called slag. A material which removes impurities is called a flux. Molten slag, being lighter than iron, collects and floats on the surface of the iron in the hearth. Large amounts of slag are used in making roadbeds, insulation, cement, and fertilizers. 4 . Tapping the Blast Furnace. The iron formed in the blast furnace is called pig iron and is tapped ( drawn off ) every five or six hours. The molten slag is tapped more fre­ quently. A single blast furnace will produce more than 1 000 tons of pig iron in one day. The pig iron, which may be poured into molds to solidify, is the most impure form of iron that is produced commercially. The chief impurity, consisting of 2 % to 5 % of carbon, makes pig iron hard and brittle. The iron cannot be hammered (forged) or welded.

COKELIRIMONESTONEORE }

3 CO t carbon monoxide

STOVE

The carbon monoxide produced by this reaction also acts as a reducing agent, com­ bining with more FeZ03 to free more iron and form carbon dioxide according to the following equation : Fe20 3 + hematite

2 00

3 CO carbon monoxide

----.

Co

2Fe + 3 C02 t Iron carbon dioxide

HEART

The blast furnace.

Molded pig iron is usually melted again and mixed with a better grade of scrap iron to form cast iron, which is somewhat softer and less likely to break. Bathtubs and steam radiators are made from cast iron. A very pure form of iron, called wrought iron, is made from pig iron by removing many of the impurities. Wrought iron is soft and can be worked into many shapes. It is used in the making of ornamental ironwork such as railings, tools and furniture. Most pig iron is used, however, in the manufacture of steel. STEEL

Steel is refined pig iron ; that is , pig iron from which much of the carbon impurity has been removed leaving just enough to provide needed hardness and strength. In addition to the controlled quantity of carbon, other metals are added to give the steel certain desired qualities.

1. The Open-Hearth Furnace. The open­ hearth furnace is basically a long, shallow basin or hearth, surrounded by firebrick. The hearth is built of steel plates covered with a coating of silica or dolomite. The type of coating used depends upon whether the charge contains acid or basic impurities. The furnace is about 1 00 feet long and 2 5 feet wide. The hearth itself is about 40 feet long and from 2 to 3 feet deep. Burning fuel (fuel oil, natural or manu­ factured gas ) mixed with preheated air passes over the charge placed in the hearth. It melts the material to convert the pig iron to steel. The air is preheated in chambers below the hearth called checker chambers. 2. The Charge of the Open-Hearth Furnace. The charge of the open-hearth furnace consists of ( a ) pig iron, ( b ) scrap steel, ( c ) limestone, and ( d ) iron are (hematite-iron oxide ) . The furnace has been preheated by a mixture of fuel and air. Limestone, iron are and scrap steel are placed in the open-hearth furnace first. In a short period of time, the tremendous heat from the flames of the burning fuel mix-

ture shooting across the hearth begins to melt the scrap steel. Some open-hearth furnaces are now equipped with tubes called oxygen lances, through which pure oxygen is added to speed up the steel-making process. When the scrap steel is partly melted, molten pig iron is poured into the charging side of the furnace. The limestone combines with impurities to form slag. As the reaction con­ tinues, the oxygen in the hematite-iron ore combines with the carhon in the pig iron, forming carbon monoxide and carbon dioxide. As this chemical reaction continues, the carbon content of the steel gradually decreases. Samples are taken periodically to assure the quality of the product. When the proper amount of carbon has been removed so that steel with a desired carbon-content has been produced, the furnace is tapped. The open­ hearth process takes about 8 to 10 hours. After tapping, the molten steel is poured into huge molds called iugot molds. When the metal has solidified, the molds are removed and the ingots are stored in pits, called soaking pits. In these pits they are heated to a tem­ perature at which they can be rolled into useful items such as beams, bars, rods and plates. Charge

Function

Pig iron

Conversion to steel

Scrap steel

Remelted to form new steel

Iron ore

Reduces the carbon content of the iron

Limestone

Removes impurities

3. The Basic Oxygen Furnace (BOF). An older method of making steel used a huge egg-shaped furnace called the Bessemer Con­ verter. Blasts of air were blown through holes at the bottom of the furnace to oxidize out impurities. Large batches of steel can be pro­ duced quickly but its quality is poor. A newly developed furnace, called the basic oxygen furnace (BOF), is a modification of the Bessemer furnace. The bottom of the basic 201

oxygen furnace is closed and pure oxygen is blown at high speed about one foot above and across the molten metal. This oxidizes out the impurities. Rapid analysis of the fur­ nace content is possible and huge quantities of high quality steel are produced in less than one hour. In the future, most steel will be made in the basic oxygen furnace. 4. Steel Alloys. Alloys are mixtures and, in some cases, complex chemical compounds, formed when different metals are melted to­ gether. Alloys can be produced in all types of steel­ making furnaces but very high quality alloys are made in the electric furnace. The electric furnace uses three giant carbon electrodes whose high-voltage current provides the heat needed to melt the charge.

tongs, powdered charcoal, and iron oxide pow­ der. ( Iron oxide powder, Fe20a, is actually hematite in powder form . )

Procedure: Mix approximately equal amounts of char­ coal and iron oxide ( 5 to 10 grams of each) i n the crucible. Test the mixture for metallic iron by inserting a pole of the magnet into the mix­ ture. What do you observe?

Light the gas burner. Adjust the air openings on the burner to get the hottest flame ( a blue flame) . Hold the crucible carefully in the tongs so that the bottom is in the hottest part of the flame. Heat for 1 0 minutes. Allow the mixture to cool, and test it with the magnet again. What do you observe?

SELF-DI SCOV ERY ACTI VITY Producing Iron from Hematite.

Conclusion:

Materials: Small porcelain crucible or evaporating dish ( a pyrex test tube will do) , gas burner, magnet,

What kind of chemical reaction has taken place?

SOME I M PORTANT STEEL ALLOYS

Composition

Properties

Uses

Stainless steel

Fe, Cr, Ni ( iron, chromium, nickel )

Resistant to corrosion

Cooking utensils, surgical instruments

Tungsten steel

Fe, W, Cr, ( iron, tungsten, chromium)

Hard, heatresistant

Cutting tools, jet engines

Alnico

Fe, Ni, AI, Co ( iron, nickel, aluminum, cobalt )

Magnetic

Powerful permanent magnets

Nickel steel

Fe, Ni ( iron, nickel )

Strong

Structural steel, armor plate, gears

Manganese steel

Fe, Mn ( iron, manganese )

Hard, strong

Safes, teeth of power shovels

Vanadium steel

Fe, V ( iron, vanadium )

Strong, elastic

Springs, gears

Alloy

202

I

R EVIEW TESTS Completion Questions For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement.

1. What is bronze and why did iron replace bronze?

2. Why is iron seldom found in the free or native state? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3. What is the meaning of the term "ore?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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4. Why has taconite become so important to the iron and steel industry? . . . . . . . . . . . . . . . . . . . . .

5. What is the meaning of the term "metallurgy?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6. When a metallurgist speaks of reducing iron ore, what does he mean by the term "reducing?"

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7. The raw materials dumped into the top of the blast furnace make up the ; . . . . .

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8. In the blast furnace, carbon and the gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . act as reducing

agents. 9. Give the function of the following structures found on a blast furnace.

(a) Bells :

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( b ) Bustle pipe : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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(c) Hearth :

NAME

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CLASS

� DATE

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__ __ __ __ __ __ __ _

203

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10. How is coke made? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11. What is "slag?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

12. How long does it take to make a batch of iron in the blast furnace? . . . . . . . . . . . . . . . . . . . . . . . . 13. What is cast iron? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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14. A very soft, pure form of iron used in making ornamental ironwork is . . . . . . . . . . . . . . . . . . . . . 15. What is steel? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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16. How is the charge of the open-hearth furnace melted? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

17. Complete the following chart by filling in the blanks with the correct answer. Function

Charge of Open Hearth

Molten material high in carbon, which will be changed into steel Limestone Removes carbon from pig iron by oxidation Scrap steel

18. Why are samples taken periodically of the molten steel? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

19. Molten steel is often poured into large molds called . . . . . . . . molds. 20. What is the purpose of the soaking pit? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

21. How does the basic oxygen furnace operate? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

What is its great advantage? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 04

NAME

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CLASS

D �ATE

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22. What is an alloy? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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23. Name the elements present in the following steel alloys :

Elements

Alloy Stainless steel Alnico Tungsten steel Manganese steel Nickel steel Vanadium steel

24. How does the electric furnace produce high quality steel alloys? . . . . . . . . . . . . . . . . . . . . . . . .

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25. What are the outstanding properties of the following alloys?

(a) stainless steel : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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(c) tungsten steel : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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( b ) alnico :

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Mu ltiple-Choice Questions In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question. 1. A compound rich in iron found in our blood is (d) fibrinogen.

( a ) hematite, ( b ) taconite, (c) hemoglobin,

2. Which of the following pairs represents the two important iron ores in the United States? (a) hematite and taconite, ( b ) magnetite and hemoglobin, ( c ) taconite and silica, (d) limestone and taconite. 3. Most iron ores occur as (a) oxides of iron, ( b ) sulfides of iron, (c) chlorides of iron, (d) all

of these. 4. Air entering the blast furnace is pre-heated in structures called (a) tuyeres, ( b ) bells, (c) hearths, (d) stoves. NAME

_______ ____

CLASS

D �ATE

__ __ __

__ __ __ __ __ __ __ _

2 05

5. CaC03 is the chemical formula for

(a) hematite, ( b ) magnetite, (c) limestone, (d) limonite.

6. Coke is primarily composed of the element (a) sulfur, ( b ) potassium, (c) hydrogen, (d) carbon. 7. The chief impurity removed from iron ore by limestone in the blast furnace is ( a ) carbon, ( b ) silica, (c) limestone, Cd) oxygen.

8. Slag is used for all of the following except (a) making roadbeds, ( b ) making cement, (c) manu­ facturing steel, (d) making home insulation. 9. Carbon is the chief impurity of ( a ) pig iron, ( b ) magnetite, ( c ) taconite, (d) hematite. 10. Cast iron is better suited for production than pig iron because it is ( a ) softer, ( b ) more brittle, ( c ) lighter in weight, (d) heavier. 11. Which of the following is true of pig iron? (a) It can be welded. ( b ) It can be forged. ( c ) It has few impurities. (d) It is very brittle .

12. All of the following are made of cast iron except ( c ) automobile fenders, (d) radiators.

(a) bathtubs,

( b ) automobile engines,

13. At the present time, the most frequently used method of producing steel is (a) the open-hearth method, ( b ) Bessemer process, (c) basic oxygen furnace, (d) electric arc process. 14. What substance is sometimes added to the open-hearth furnace to speed up the steel making process? ( a ) silica, ( b ) oxygen, ( c ) carbon, (d) cobalt.

15. What was the name of the older egg-shaped furnace that was used to make steel? (a) Bessemer converter, ( b ) open-hearth furnace, (c) basic oxygen furnace, (d) blast furnace.

Matching Questions In the space at the left of each item in Column A, place the letter of the term or expression in Column B that is most closely related to that item. Column B

Column A

a. Stoves b. Aluminum c. Slag d. Iron e . Extraction f· Refining g. Bituminous h. Tungsten steel i . Skip cars j. Forging k. Stainless steel I. Tuyeres m. Anthracite

1. R emoving impurities from ores

2. Molten material floating on top in the hearth of a blast furnace 3. Hammering metal 4. Kitchen utensils and appliances 5. Cutting tools, jet engines

6. Preheat air entering blast furnace 7. Soft coal used to make coke 8. Transports the charge to the top of the blast furnace 9. Transports hot air into the interior of the blast furnace 10. Most abundant metal in earth's crust

2 06

NAME

_______

CLASS,�

DATE

_ _

_ _ _ _ _ _ _ _

Chapter

23

O RG A N I C CH E M I STRY Organic chemistry is the branch of chemistry concerned with the study of compounds con­ taining carbon. These include compounds that exist in nature as well as those that are syn­ thetically produced. Nearly all carbon com­ pounds are classified as organic, with the exception of such compounds as carbon di­ oxide, carbon monoxide and carbon-contain­ ing minerals called carbonates. The term "organic" is sometimes used to describe living or dead plant and animal life, since protoplasm, the living material of cells, always contains the element carbon. Proteins, carbohydrates, fats and vitamins are organic substances found in many types of food. The theory that organic compounds could only be produced by living organisms was dis­ proved in 1 82 8 . A German scientist, Friedrich Wohler, produced the organic compound urea from an inorganic, non-living substance. This was a giant step forward, and resulted in freeing the field of organic chemistry from dependence upon products made by living things. It also led to the synthesis of many organic compounds not produced by living things. These include medicines, vitamins, hormones, plastics, synthetic rubber, dyes, and fertilizers. Today, well Qver a million organic compounds are known to man and the list is constantly growing. Carbon, the element found in all organic compounds, is the eleventh most abundant element. It owes its importance to its ability to form more compounds than any other element on earth . Carbon occurs in nature in both free and chemically combined forms. Free carbon is found chemically uncombined in crystalline forms such as diamonds and graphite. Carbon also occurs free in the amor-

phous ( shapeless ) form, in which the crystals are so small ( submicroscopic ) that the mate­ rial has a non-crystalline appearance. Some examples of amorphous carbon are : coal, coke, charcoal, lampblack, bone black, and carbon black.

A rrangement of carbon a toms in the diamond.

CRYSTALLI N E FO RMS OF CARBON 1 . Diamond. The diamond is the hardest known natural substance because of the ar­ rangement of the carbon atoms in the crystal­ line molecule. The diamond is considered a precious gem because of its rarity and its ability to reflect and refract (bend ) light to produce a brilliant sparkle. Because of its extreme hardness, it is used industrially in cutting tools, abrasives, in dies that reduce the diameter of wire, and in phonograph needles. Small industrial diamonds are now made synthetically by applying tremendous heat and pressure to certain carbon com­ pounds. 207

2. Graphite. Graphite is a softer form of carbon than the diamond because of a dif­ ferent arrangement of the carbon atoms in the crystalline molecule. Graphite is frequently used in pencils, lubricants, crucibles (con­ tainers that can withstand extremely high tem­ peratures) , and in making blocks for nuclear reactors, which act as moderators to slow down free neutrons.

a reducing agent to remove oxygen from oxide ores, such as the iron ore hematite ( Fe203 ) , and in the production of gaseous fuels. 3 . Charcoal. Charcoal is made by the destructive distillation of wood. In this proc­ ess, many of the volatile materials are driven from the wood. Charcoal is used as an adsorb­ ing agent and, to a minor extent, as a fuel. An adsorbing agent is a substance which attracts and holds other substances (gases and liquids ) to its surface. Charcoal is used as an adsorbing agent in many filters to remove unwanted impurities, colors, odors and, in some cases, poisons. It is used as an adsorbent in gas masks, cigarette filters, aquarium filters, and in the refining of sugar ( removing color­ ing matter from brown sugar ) . S ELF-DI SCOVERY ACTIVITY

Exploring Destructive Distillation. Arrangement of carbon atoms in graphite.

AMORPHOUS (NON -CRYSTALLI N E) CAR B O N 1 . Coal. Coal is formed b y the slow chemi­ cal breakdown of plant remains over a tremen­ dous length of time. In addition to bacterial decomposition, the plant material is subjected to great heat and pressure. The first stage in the coal-formation process is peat, a product of partial decomposition. Further decomposition accompanied by heat and pressure results in the formation of lignite or brown coal. Continuing heat and pressure change lignite into soft ( bituminous ) coal and finally hard (anthracite ) coal, a purer form of carbon. Coal is used primarily as a fuel. Soft coal is also used in the production of coke.

2. Coke. Coke is made by heating bitumi­ nous coal in the absence of air. This process, called destructive distillation of soft coal, drives off the volatile ( readily vaporizable ) substances, coal gas and ammonia, found in the soft coal. Coke is used as a fuel, and as 208

Materials: Gas or alcohol burner, pyrex test tube, wood splints, one-hole rubber stopper, test tube clamp or tongs, protective gloves, small piece of glass tubing to fit stopper, matches, ring­ stand.

Procedure: Fill all space in the pyrex test tube with wood pieces, Insert the rubber stopper with the glass tubing in the hole. Heat the bottom of the test tube over the flame of the burner.

GLAS TUBING IN STOPPER ANDRINGSTAND CLAMP /

Observations:

,

WOODSPLICHIPNSTSFILORLING TEST TUBE --GASALCOHOLBURNEROR /

I/

What begins to come from the glass tube?

After the process has gone on for several minutes, place a lighted match at the open end of the glass tube. Observe. . . . . . . . . . .

.

.

. . .

What change in appearance, if any, is taking place inside the test tube? (When all changes stop, turn off the burner and allow materials inside tube to cool before examining them . )

its outer shell with other atoms to form co­ valent bonds. Carbon atoms are also unique in that they will readily unite with other carbon atoms, forming, in some cases, very long carbon chain compounds as well as ring compounds. The covalent bond ( shared electrons ) is often illustrated by two dots representing a pair of shared electrons. A single line (-) , called a valence bond, is also used to represent a covalent bond.

This process you are observing is the de­

H

H � C ·H

H-C-H

H

H

I I

•

structive distillation of wood. Describe this process as you h ave observed it. . . . . . . . . . .

H

.0

=

=

HYDROGE LECTRON CARB ON NELEECTRON

Methane-CH.

H I

H I

H I

H I

H-C-C-C-C-H 4. Lampblack and Carbon Black. Lamp­ black is commonly seen as soot produced when fuels with high carbon content, such as kerosene, are incompletely burned. The soot produced by the incomplete combustion of natural gas is called carbon black. Carbon black and lampblack are used in making shoe polish, india ink, carbon paper , printer's ink, paint pigments, and rubber tires. 5. Boneblack. Boneblack, also known as animal charcoal, is made by the destructive distillation of bones. It is frequently used as an adsorbent to decolorize liquids. A brown sugar solution, for example, is converted to a colorless sugar solution by passing it through a filter containing boneblack. T H E C O M PO U N DS OF CAR B O N

There are more carbon compounds in nature than compounds of any other element because of the properties of the carbon atom. One of these properties is the ability of the carbon atom to share readily the four electrons in

I

H

I

H

I

H

I

H

Butane-C4Hl0

The formulas of these organic or carbon compounds are called structural formulas. Structural formulas show not only the number and kinds of atoms present, but also indicate the location and bonding of the atoms within the molecule. Another advantage of the struc­ tural formula is that it reveals the covalent linkages between carbon atoms and the atoms of other elements. Still another reason for the tremendous number of carbon compounds is the formation of isomers. Isomers are compounds whose molecules contain the same number and kinds of atoms as the original compound but in different arrangement. Isomers have the same molecular formula but have a different struc­ tural formula. For example, the organic compound called butane ( molecular formula C 4HIO) can be written as a structural formula with its carbon atoms arranged in a straight chain, or as a molecule in which one of the carbon atoms forms a side chain. The straight209

chain molecule of butane is called normal butane (n-butane) and the branched-chained isomer is called isobutane. The prefix iso- is used to designate all compounds in which the carbon atoms are arranged in a branched chain.

H

H

I

H

I

H

I

I

H-C-C-C-C-H

I

I

H

I

H

H

I

H

H

H

H

I I I H-C-C-C-H

� I �

H-C-H

I

H

/sobutane-C!,H10

COMPARISON OF O RGANIC AND INORGANIC COMPOUNDS

Organic

Inorganic

1 . Generally insoluble in water

Generally soluble in water

2. Generally soluble III organic liquids such as carbon tetrachloride or al­ cohol

Generally insoluble in organic liquids

3 . Form no ions in a water solution

Form ions in a water solution

4. Organic reactions occur slowly

Inorganic reactions often occur rapidly

5 . Many organic com­ pounds burn readi­ ly 210

Few inorganic com­ pounds are combus­ tible

HYDROCAR BONS

Hydrocarbons are organic compounds con­ taining only carbon and hydrogen atoms. Many thousands of such carbon compounds are known. In fact, most organic compounds are hydrocarbons. Since carbon atoms are capable of sharing electrons with each other, they tend to form long chains. The gas methane ( CH4 ) is the simplest hydrocarbon, having only one carbon atom. Methane is the first in a series of hydro­ carbons called the methane or the paraffin series. The general formula for any member compound of this series is CnH2n + 2, where n stands for the number of carbon atoms. A series of hydrocarbons contains compounds that are structurally related and may have similar chemical or physical properties. As one continues in such a series, the number of carbon atoms increases and the molecular weight also increases. The low-molecular weight members of the methane series are gases ; the intermediate-weight members are liquids ; the heavier members are solids. Other series of structurally related hydro­ carbons include the ethylene series with a gen­ eral formula of CnH2n, and the acetylene series with a general formula of CnH2n-2. In each of these series of hydrocarbons, the carbon atoms are united in a chain. The benzene series is unique, however, because the carbon atoms are united in a six-sided ( hexagonal) ring. Benzene ( C6H6 ) is the simplest member of this series of hydrocarbons and its structural formula is written as follows :

�b H-l�"C-H

H

o-� II-, �c/ !

H

Compounds of the benzene series are known as ring or aromatic compounds.

SOME MEMBERS OF THE METHANE SERIES

Name

Methane

Molecular Formula CnH2n + 2

Structural Formula

CH4

H I H-C-H

State of Matter

Gas

I

H H Ethane

Propane

C2H6

Pentane

C5H12

H

H

I

Gas

I

I

H H H I I I H-C-C-C-H I

H C4H1O

H

H-C-C-H

C3HS

Butane

I

I

H

I

H

H H H H I I I I H-C-C-C-C-H I I I I H H H H H I

H I

H I

Gas

H I

H I

H-C-C-C-C-C-H I , I I I H H H H H

Gas

Liquid

2. Light the gas burner. With the tongs hold the piece of bread just above the flame for SELF-DISCOVE RY ACTIVITY

several minutes . What do you observe? . . . . .

Examining Organic Materials for Carbon.

Support your observations. . . . . . . . . . . . . .

Materials: Candle, beaker of ice water, gas burner, tongs, piece of bread, old metal spoon, gloves, sugar.

Procedure: 1 . Light the candle. Hold the beaker of ice water inside the candle flame so that the flame "licks" around the bottom of the beaker. What

3. Hold the spoon that is h alf-filled with sugar over the burner flame. Make certain the spoon is an old one, and wear protective gloves. After several minutes, what do you observe?

do you observe? . . . . . . . . . . . . . . . . . . . . . . .

Support your observations. . . . . .

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Support your observations . . . . . . . . . . . . . .

211

Conclusions: Which, if any, of the materials you tested

Try your test with your teacher's assistance, if necessary. What are your results? . . . . . . . .

contained organic compounds? . . . . . . . . . . .

How do you know? . . . . . . . . . . . . . . . . . . How are the three investigations in this Can you think of a test you could make to find out with greater certainty if any of the residues you observed were actually carbon?

212

activity similar to the distillation activity on . page 208 ? . . . . . . . . . . . . . . . . . . . . . . . . . . .

R EVIEW TESTS Completion Questions For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement. 1. Mineral compounds called . . . . . . . . . . . . . contain the element carbon but are not considered organic compounds. .

2. What are five different man-made compounds that are organic in composition? ( a ) (b)

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3. The theory that carbon compounds could only be produced by living organisms was disproved .

when . . . . . . . . . . . . . . . . . . . . . . synthesized . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4. Why is the term "organic" sometimes used to refer to substances derived from living material?

5. Two forms of chemically uncombined (free ) carbon are: (a) . . . . . . . . . . , and ( b ) . . . . . . . . . . . 6; Diamond and graphite contain atoms arranged in the form of a . . . . . . . . . . . . . . . . . molecule.

7. What is the meaning of the term "amorphous?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8. When cut properly and polished, the diamond is capable of producing a brilliant sparkle because of its ability to . . . . . . . . . . and . . . . . . . . . . light. .

9. What are three industrial uses for diamonds? (a) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ,

(c )

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10. How are industrial diamonds made synthetically? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11. Why is it scientifically incorrect to refer to a pencil as a "lead" pencil? . . . . . . . . . . . . . . . . . . .

12. What are the scientific names for the following?

(a) soft coal -

( b ) hard coal - . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13. How is coal made?

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D � ATE

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14. How does nature change soft coal into hard coal? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

NAME

.

_______________

.

213

15. Why is coke an excellent reducing agent? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

16. What is the meaning of the term "destructive distillation?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

17. What is a product made by the destructive distillation of wood? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18. What is the meaning of the term "adsorbing agent?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

19. As an adsorbing agent, charcoal may be used to remove (a)

( b ) . . . . . . . . . . . . . . . . . . . . . . , ( c)

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. , (d) . . . . . . . . . . . . . . . . . . . . .

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20. When carbon fuels such as kerosene are incompletely burned, a soot . . . . . . . . . . . . . . . . . . . . is formed. The soot produced by the incomplete combustion of natural gas is called . . . . . . . . . . . . .

.

21. What are three uses for the residue formed by the incomplete combustion of carbon fuels?

(a) . . . . . . . . . . . . . . . . . , ( b ) . . . . . . . . . . . , (c)

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22. What is an important use of boneblack? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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23. Three reasons why there are more organic compounds than non-organic compounds are :

(a)

(b)

(c)

24. The sharing of electrons between two atoms forms a ( an ) . . . . . . . . . . . bond. 25. What is meant by a "structural" formula? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

26. What is the meaning of the term "isomer?" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

27. Methane is the first in the series of hydrocarbons called the methane or . . . . . . . . . . . . . series.

28. Hydrocarbons of high molecular weight would exist in the . . . . . . . . . state. 214

NAME

______

CLASS

D �ATE

__ __ __

__ __ __ __ __ __ __ _

29. What is the structural formula for the following?

( a) normal butane :

( b ) isobutane :

30. The formula C5H1 2 represents the hydrocarbon called . . . . . . . . . which is a . . . . . . . . . at room temperature. 31. Three other series of hydrocarbons other than the methane series are : (a) . . . . . . . . . . . . . . . . . . ,

(b)

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32. In what way is there a unique arrangement of the atoms within the molecules of hydrocarbons belonging to the benzene series?

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33. In the space at the right draw two diagrams to represent the structural formula for the hydrocarbon called benzene.

34. Why are organic liquids poor conductors of electricity?

35. Organic reactions usually occur very . . . . . . . "

and often need a catalyst.

Multiple-Choice Questions In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question. 1. All organic compounds must contain the element (d) sodium.

(a) hydrogen ,

( b ) nitrogen,

(a) carbon monoxide,

2. Which of the following is an organic compound? (c) sodium carbonate, (d) carbon tetrachloride.

3. Today, the number of known organic compounds in existence is over ( b ) two million, (c) one million, (d) fifty thousand. 4. The organic living material of a cell is (a) urea,

( b ) protoplasm,

(c) carbon,

( b ) carbon dioxide,

(a) one-half million,

(c) plasma,

(d) nucleus.

5. The eleventh most abundant known element is (a) hydrogen, ( b ) chlorine, (c) magnesium, (d) carbon. 6. Which of the following is not a form of amorphous carbon? (a) coke, ( b ) charcoal, (c) graphite, (d) lampblack. NAME_______CLASS

Ll DATE.

_ _ _

--,-___

_ _ _ _

215

7. Coke is manufactured by the process of ( a ) destructive distillation, ( b ) condensation, (c) ad­ sorption, ( d ) bacterial action. S. An example of an adsorbing agent is

(a) carbon tetrachloride,

( b ) charcoal, (c) graphite,

(d) diamond.

9. Boneblack is also known as (a) coke, ( b ) carbon black, (c) lampblack, ( d) animal charcoal. 10. What is the general formula for the members of the methane group? ( c ) CnH2n +2, ( d) Cn H2n-2 .

(a) CnHn, ( b ) CnH2n,

11. Isomers differ in their ( a ) molecular formula, ( b ) structural formula, ( c ) weight, (d) number of atoms. 12. Which of the following is not a hydrocarbon?

(a) CH4,

( b ) C2H6,

(c) CH3Cl, (d) C6H6• 13. If a compound found in the methane series of hydrocarbons has eight carbon atoms in a single molecule, how many hydrogen atoms would be present in the molecule? ( a ) 1 6, ( b ) 8, (c) 1 8 , ( d ) 14. 14. As one continues in the series of hydrocarbons, the number of carbon atoms ( b ) decreases, (c) remains the same, (d) increases and then decreases.

( a ) increases,

15. A hydrocarbon had a formula C6H10. To what series of hydrocarbons does it belong? ( a ) methane series, ( b ) ethylene series, ( c) benzene series, (d) acetylene series.

Matching Q uestions

In the space at the left of each item in Column A, place the letter of the term or expression in Column B that is most closely related to that item. Column A 1. Lubricant 2. Activated charcoal 3. Destructive distillation of bones 4. Branched chain isomer 5. C 6H 6 6. Contains carbon but not classified as organic

7. Members of the benzene series

9. Removes oxygen from iron ore

Column

B

a. b. c. d.

CO2 Benzene Aromatic compounds Graphite e. C 12H 220 11 f . Carbon tetrachloride g. Boneblack h . Coke I. Isobutane . j U sed in gas masks k. Lampblack I. Diamond m. Propane

10. Hardest natural element

216

NAME _______ CLASS,

DATE

___

_ _ _ _ _ _ _ _

Chapter

24

C H E M ICAL A DVANCES There is scarcely an industry or an indi­ vidual that has not been affected by the revolutionary advances in chemical research. The many products that resulted from this basic research have made it possible for us to enjoy a healthier and more pleasurable life. Some of the more important chemical contri­ butions will be discussed below. H EALTH

The products of chemistry have helped in­ crease the life span of people born in the United States from 47 years in 1 900 to over 70 years at the present time. To a large extent, this increased life expectancy is the result of the discovery of new medicines through pharma­ ceutical research. These medicines have dramatically reduced the number of deaths from infectious diseases . Over 90% of all pharmaceutical compounds currently being produced were discovered within the last 1 5 years. The following are some of the many note­ worthy contributions that enable all of us to live longer and more fruitful lives : ( a ) antibiotics such as penicillin ; ( b ) vaccines to prevent polio, smallpox, typhoid fever and other infectious dis­ eases ; ( c ) vitamins to prevent and treat certain nutritional diseases ; ( d ) hormones to treat disorders of the ductless or endocrine glands. Biochemical research is beginning to un­ ravel the mysteries involved in heredity and the control of cellular activity. Scientists are investigating the molecular structure and chemical properties of DNA ( deoxyribo­ nucleic acid ) and RNA ( ribonucleic acid ) , important organic compounds found within the nucleus of the cell. The results of this research, if successful, will be milestones in

medical history for they may enable man to understand, treat and prevent many diseases. In addition, they will provide insight into growth and life itself. I N DUSTRY

The industrial and economic development of our country is closely related to advances in the science of chemistry. Basic discoveries in chemistry have led to the development and growth of industries such as petroleum and petroleum products, plastics, synthetic rubber and textiles, metals, glass, foods, fertilizers, paints, pharmaceutical products, dyes, soaps and detergents, paper, building materials , and rocket and nuclear fuels, to mention only a few. The area of chemistry related to petroleum products is known as petrochemistry. 1. Petroleum. Petroleum, commonly called crude oil, is a mixture of thousands of hydro­ carbons. Useful hydrocarbons are separated from petroleum by the process of fractional distillation. In this process, crude oil is heated in a furnace and the reSUlting vapors and the liquid which is not vaporized enter a tall tower called a fractionating tower. The un­ vaporized liquid, called the residue, is drained from the bottom of the tower. Many useful products such as asphalt, heavy fuel oil and wax are obtained from this residue. The use of fractional distillation to separate and collect different hydrocarbons is based upon the principle that various hydrocarbons boil, vaporize and condense at different tem­ peratures. Lighter hydrocarbons, with lower boiling points, pass off as a vapor and condense as a liquid in the cooler, upper portion of the tower. Gasoline passes off as a vapor and is condensed later, while kerosene passes off as a liquid. Heavier hydrocarbons, with higher boiling points, such as fuel oils and lubricat­ ing oils, condense in the hotter, lower portion 21 7

J

CONDENSfP KEROSENE

FUEL OIL LUBRIOICLATING STEAM ,/

- "-

Fractionating tower.

of the tower, from which they are drawn off. The amount of gasoline obtained by the fractional distillation of petroleum is often increased by the process of cracking. Cracking is the decomposition of the large hydrocarbon molecules, such as those found in fuel oils, into the simpler, more volatile molecules of gasoline. Sometimes a reverse process is used in which smaller hydrocarbon molecules are combined to form larger molecules of gaso­ line. This process is called polymerization. Efficient operation of the modern auto­ mobile engine requires the proper burning of the gasoline fuel. This is accomplished by having a single, controlled explosion (burn­ ing ) of gasoline in the cylinders. Because of the great heat produced in high compression engines, multiple, uncontrolled explosions called "knocking" may occur. Knocking re­ sults in the inefficient burning of the gasoline accompanied by wasted power. Gasolines of better quality having good anti-knock prop­ erties are composed of side-chain isomers in­ stead of straight-chain hydrocarbons. The anti-knock quality of a gasoline may also be 218

improved by adding tetraethyl lead ( ethyl gasoline) which slows down the rate at which gasoline will burn in the engine. Today, new chemicals have been developed to replace the lead. 2. Plastics. Plastics are complex organic compounds which can be easily shaped by heat or pressure. Plastics are usually produced by polymerization ( the process by which smaller molecules are combined to produce larger molecules ) . The simple starting sub­ stances are generally called monomers and the large complex molecules formed from these monomers are called polymers. The American scientist John Hyatt produced the first synthetic plastic, celluloid, in 1 8 6 8 , in his search for a suitable substitute for ivory. Plastics are classified into two types : ( a ) thermosetting, and ( b ) thermoplastic. Ther­ mosetting plastics are those which, after for­ mation, cannot be softened by further heat treatment. Examples are Bakelite, commonly used for telephones, radios and television cabinets, and melamine, used in tableware. Thermoplastic plastics are those which can be softened by heat and reshaped after forma­ tion. Some common examples include plexi­ glas ( lucite ) , used to make dentures and lenses, polyethylene, used for freezer bags and squeeze bottles, polystyrene, used for trans­ parent boxes and containers, celluloid, used for making film and piano keys, and cel­ lophane and saran, used for clear wrapping material. Some additional thermoplastics and their uses are : Teflon, which provides a slip­ pery, non-sticking surface. This plastic is also resistant to extreme temperature changes. These properties make Teflon well adapted for use in cooking utensils, tubing and other applications. Polyvinyl acetate or polyvinyl chloride are plastics used in lightweight rain­ coats, cement (glue ) and imitation leather.

3. Rubber. Natural rubber is a polymer consisting of several thousand molecules of a hydrocarbon monomer called isoprene ( C5Hs ) . In the manufacture of rubber, the milky, elastic sap, latex, of the rubber tree is

mixed with a weak acid ( acetic acid ) which causes the latex to coagulate. It is then washed and dried to produce raw rubber, a weak and inelastic substance. In 1 839 , the American, Charles Goodyear discovered vulcanization, a process in which sulfur is added to raw rubber and the mixture is heated to make the rubber elastic and strong. Today, carbon black is added to rubber to m ake it more resistant to abrasion. Other chemicals, called antioxidants, are also added to reduce the destruction of rubber by oxygen. More synthetic rubber is used today than natural rubber. Synthetic rubber can be manu­ factured from coal, natural gas and petroleum. Some synthetic rubbers include neoprene and thiokol, both of which are highly resistant to the action of oil and gasoline. GR-S is a type of rubber that has excellent resistance to abrasion and oxidation and is non-squealing. Since GR-S provides for quick stopping on wet surfaces, it is used in the manufacture of tires. Butyl rubber ( GR-I ) is used in the manufacture of inner tubes, and GR-N rubber is used for making self-sealing tires. Scientists have recently discovered a way to replace some of the carbon atoms in the rubber molecule with silicon atoms to make silicone rubber. This type of rubber remains elastic at extremely high and low temperatures, and is not affected by hot oil. 4. Synthetic Fibers. Synthetic fibers such as rayon, nylon, dacron and orIon have made an important contribution to the growth of the textile industry. Rayon, the first synthetic fiber produced, was made from cellulose obtained from cotton. Although rayon can be manufactured inex­ pensively, with a more lustrous finish than silk, it burns easily and is weakened by mois­ ture and perspiration. Acetate rayon, on the other hand, retains its strength when wet, is unaffected by perspiration and burns slowly. Care must be taken in ironing acetate rayon, however, or it will be destroyed by the heat. Nylon was first manufactured in the United Stat,;!s in 1 93 8 . It is made from raw materials

obtained from coal tar, air and water. Because of its strength, nylon is used to make hose, parachutes, shirts, tires and other products in which fiber strength is essential. Today, there are so many man-made fibers that the use of brand names tends to be con­ fusing. For this reason, government regulations require that manufacturers use certain specific names that are related to the chemical makeup of the fibers. Although trademark names, such as Orion, A crilan, and Dacron, may still be used, the government-designated names must also be included. The 1 7 required names are listed below : 1. Glass fibers, such as fiberglass and polyglas 2. Metallic fibers 3. Rubber fibers Fibers made from cellulose 4. Rayon 5. Acetate 6. Triacetate

Nitrogen-base fibers 7. Azlon 8. Acrylic 9. Modacrylic 10. Nytril 1 1 . Spandex 12. Nylon

Vinyl fibers ( CHzCH) 13. 1 4. 1 5. 1 6. 1 7.

Vinal Vinyon Saran Polyester Olefin

5. Silicones. Silicones are organic com­ pounds, the molecules of which contain silicon atoms as well as carbon atoms. These com­ pounds possess unique properties that make them highly useful. They are unaffected by extreme temperature variations , can prevent objects from sticking together, and are water repellant. Silicones are being used in the manufacture of electrical insulation, waxes, lubricants and waterproofing materials. 219

CONS ERVATION OF RESOU RCES

The tremendous growth of industry is taxing our natural resources to an ever-increasing extent. The science of chemistry is helping conserve these resources by providing the knowledge and technology required to make better use of and increase the production of these resources. In addition, scientists are ap­ plying newly discovered principles and meth­ ods in attempts to provide substitutes for scarce commodities . The use of fertilizers and insecticides has greatly increased the production and quality of our food. Refrigerants and new packaging methods have enabled us to prevent food spoilage and loss of vitamin content for con­ siderable periods of time. Chemical investi­ gation into new sources of food, such as farming the ocean, may provide an answer to the world's food problems. Chemistry may soon provide the answers necessary for developing an economically practical method of desalting ocean water to solve the problem of the present fresh-water shortage .. New methods of extracting and re­ fining many of our non-renewable minerals have been developed to prevent waste and provide us with new sources of supply. Plastics and other chemical substitutes are replacing wood and metal, reducing the drain on these natural resources. Corrosion-resistant chemi-

220

cals will prevent deterioration of metals. Nu­ clear fuels may, some day, completely replace coal, petroleum and other fuels which are being rapidly depleted. Basic research in chemistry is providing the knowledge and skills that will enable men to live a longer, more prosperous and healthful life. S ELF-DI SCOVERY ACTIVITY Preparing a Polymer.

Materials: Evaporating dish or crucible, alcohol or gas burner, tongs, container of ice water.

Procedure: Heat some powdered sulfur on a low flame in the evaporating dish. When most or all of the sulfur has melted, quickly but carefully use the tongs to help pour the material into the ice water.

Observations: Examine some of the powdered sulfur. How would you describe it? . . . . . . . . . . . . . . . . .

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R EVIEW T ESTS Completion Questions For each of the statements or questions below, write the word or phrase in the space provided that best answers the question or completes the statement. 1. Chemical research and technology have contributed to your health in the following ways :

(a)

(b)

(c)

(d)

(e)

2. How may biochemical research into the structure and chemical activity of DNA and RNA .

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3. What is petroleum? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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4. How is petroleum refined? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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help mankind?

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s. What are the characteristics of the hydrocarbons drawn off from the top and the lower portions

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6. The reverse process of cracking is called

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In this process, . . . . . . .

molecules are combined to form . . . . . . . molecules. NAME

__ __ __ __ __ __ __ __ __ ______ _

CLASS

-LJ DATE

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221

7. In which two ways are the anti-knock qualities of gasoline increased?

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9. What is the difference between a thermoplastic and a thermosetting plastic? . . . . . . . . . . . . . .

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10. Melamine, a plastic commonly used in making plastic dishes is a . . . . . . . . . . . . . . . . . . plastic,

while plexiglas, used to make dentures, is a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . "

plastic.

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12. What is natural rubber? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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13. What is latex? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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14. What is done when rubber is vulcanized? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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15. Why are anti-oxidants added to rubber? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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11. Why is the plastic Teflon used in cooking utensils?

16. Which synthetic rubbers are noted for the following characteristics?

(a) non-squealing, resistant to abrasion : ( b ) highly resistant to oil and gasoline : 17. What is a silicone rubber?

222

NAME

_ _ _ _ �.

_______

CLASS,

___

DATE

_ _ _ _ _ _ _ _

18. What raw materials are used in manufacturing nylon? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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19. The raw materials used to make dacron are obtained primarily from . . . . . . . . . . . . . . . . . . . . . . 20.

Specifically, how are results of chemical research helping to solve the following conservation problems? (a) Increasing the production of food : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

( b ) Prevention of food spoilage and loss of vitamin content:

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Multiple-Choice Questions

In each of the following questions, circle the letter preceding the word or phrase that best completes the statement or answers the question. 1. What percentage of the pharmaceutical products now manufactured were discovered within the past fifteen years? ( a ) 60, ( b ) 70, .( c ) 80, (d) 90. 2. Of the following industries, which has not benefitted from the fruits of chemical research? ( a ) plastics, ( b ) metals, ( c ) textiles, ( d ) all have benefitted. 3. Gasoline passes out of the fractionating tower as ( a ) a liquid, ( b ) a vapor, (c) a solid, (d) any one of these. 4. The cracking process is used to ( a ) combine small molecules into larger ones, ( b ) break down large molecules into smaller . ones, ( c ) both of these, ( d ) neither of these. 5. Monomers are ( a ) small molecules, ( b ) medium-sized molecules, (c) large molecules, (d) types of plastics. NAME _______ CLASS

---DATE, -"-'

_ _

_ _ _ _ _ _ _ _

223

6. Polyethylene is used in the production of (a) squeeze bottles, ( b ) dishes, ( c ) lenses, ( d ) cooking utensils.

7. Of the following, which is a property of raw rubber? ( a ) highly elastic, ( b ) black in color, ( c) inelastic, ( d ) brittle. 8. Carbon black is added to rubber in order to increase its ( a ) elasticity, ( b ) hardness, (c) resist­ ance to abrasion, ( d ) ability to withstand temperature extremes. 9. Which of the following is not a quality of silicone rubber? ( a ) elastic at high and low temperature extremes, ( b ) unaffected by hot oil, ( c ) has fewer carbon atoms than normal rubber, ( d ) is used for self-sealing tires . 10. Which of the following is not a synthetic fiber used in the textile industry? (a) azlon, ( b ) radon, ( c ) nylon, (d) vinal. 11. Rayon is made from ( a ) air, ( b ) cellulose, (c) coal tar, ( d ) silicones. 12. Which of the following is a nitrogen-base fiber? (a) wool, ( b ) rayon, ( c ) spandex, ( d ) linen.

13. A synthetic fiber that is noted for its great strength is ( a ) rayon, ( b ) acetate, ( c ) spandex, (d) nylon.

14. Which of the following is not a property of silicones? ( a ) brittleness, ( b ) can prevent objects from sticking together, ( c ) water repellant, (d) unaffected by temperature extremes.

15. Silicones are used industrially ( a ) in automobile tires, ( b ) in plastic bottles, (c) as lubricants, ( d) in unbreakable toys.

Matching Questions

In the space at the left of each item in Column A, place the letter of the term or expression in Column B that is most closely related to that item.

1. Discovered vulcanization

2. Waterproofing material and lubricant 3. Used in parachutes and hosiery 4. Ethyl gasoline 5. Petroleum refining 6. Polymer 7. Used

III

freezer bags

8. Used in telephones 9. Used III the vulcanization of rubber

B

Column

Column A

a. b. c. d. e.

f.

g.

h. i.

j. k.

I. m.

Nylon John Hyatt Charles Goodyear Giant molecule Bakelite Silicon Silicones Tetraethyl lead Chemical code to heredity and cellular control Fractional distillation Polyethylene Sulfur Latex

10. DNA

224

NAME

______

CLASS

� DATE

__ __ _

____ __ __ __ __ __ _

D I ST I N G U I S H E D S C I E N T I STS Arilpere, Andre ( 1 775- 1 8 3 6 ) , French physicist, first showed the relationship between mag­ netism and electricity. The ampere, the unit of flow of electric current, is named after him. Archimedes (287-2 1 2 B.C.), Greek mathema­ tician , invented the combination of pulleys for lifting weights, and the revolving screw for raising water. He is best known for his princi­ ple that a submerged body displaces a volume of water equal to its own volume. Becquerel, Henri ( 1 8 52- 1 908), French physi­ cist, investigated uranium and other radio­ active elements ; the rays emitted by these sub­ stances are known as "Becquerel rays." Bernoulli, Daniel ( 1 700- 1 7 8 2 ) . Swiss physi­ cist, called the founder of mathematical phys­ ics. He is best known for his discovery that the pressure of a fluid decreases as the velocity in­ creases. Bessemer, Henry ( 1 8 1 3 - 1 8 9 8), English engi­ neer who discovered a method of changing pig iron into steel quickly and cheaply. His fur­ nace is called the Bessemer converter. Bunsen, Robert Wilhelm ( 1 8 1 1 - 1 8 99), Ger­ man chemist, pioneered with Gustav Robert Kirchhoff in spectrum analysis; invented the spectroscope, the ice calorimeter and the Bun­ sen burner. Celsius, Anders ( 1 7 0 1 - 1 744), Swedish astron­ omer, first to describe ( 1 742) the Centigrade thermometer which also bears his name. Chadwick, Sir James ( 1 8 9 1 ), English physicist specializing in radioactive research; discovered the neutron - the uncharged parti­ cle in the nucleus of the atom.

Curie, Mme. Marie ( 1 8 67 - 1 934) , French phys­ icist of Polish birth, who with her husband, Pierre Curie, carried on research with radio­ active minerals which led to the discovery of radium. Einstein, Albert ( 1 8 79-1 955), German-Ameri­ can theoretical physicist established his famous law which expresses mathematically the rela­ tionship between matter and energy, E = mc2 • Fahrenheit, Gabriel Daniel ( 1 686-1 7 3 6), in­ vented the mercury thermometer and devised the Fahrenheit scale commonly used in Britain and the United States. He discovered the fact that the boiling point of liquids other than water varied with the changes of atmospheric pressure. Faraday, Michael ( 1 7 9 1 - 1 8 67), English chem­ ist and physicist, discovered two chlorides of carbon, and benzene; liquefied several gases; discovered the electrochemical equivalents of metals, the electrolysis laws, and electromag­ netic induction. Fermi, Enrico ( 1 90 1 - 1 9 54) , Italian physicist, worked in transmutation of elements and radio­ activity; first to control the release of nuclear energy by slowing down neutrons. Galileo, Galilei ( 1 564- 1 642 ) , Italian physicist and astronomer, proved that all falling bodies, independent of their weight, descend with equal velocity; made the first thermometer, discovered the law of the pendulum, con­ structed the first telescope with which he was first to observe the seas and craters of the moon. 225

Goodyear, Charles ( 1 8 00- 1 8 60) , American in­ ventor, experimented with treatment of rubber and developed vulcanization process. Hahn, Otto ( 1 8 7 9 - 1 968), German chemist, fa­ mous for work on atomic fission. Henry, Joseph ( 1 797-1 8 7 8), American physi­ cist, invented spool type electromagnet ; built device for lifting heavy weights by magnetic attraction. Huygens, Christian ( 1 629- 1 695), Dutch physi­ cist and astronomer, constructed powerful tele­ scopes, and improved methods of grinding and polishing lenses; first to use pendulum in clocks; investigated polarization of light; de­ veloped wave theory of light. Hyatt, John Wesley (1 8 3 7 - 1 920), American inventor, discovered fundamental principle used in making celluloid. Lavoisier, Antoine (1 742- 1 794), French chem­ ist, is called the "father of modern chemistry." He named oxygen, hydrogen and nitrogen and explained combustion as the union of the burn­ ing substance with the part of the air that he called oxygen . Mach, Ernst ( 1 8 3 8 - 1 9 1 6), Austrian physicist and philosopher. The velocity of sound in air (Mach 1) is named after him. Maxwell, James Clerk ( 1 8 3 1 - 1 8 7 9), Scottish physicist and astronomer ; investigated color perception and color blindness; worked on theory of electromagnetism; demonstrated that electromagnetic acti�n travels through space in transverse waves similar to those of light and having the same velocity. Mendeleyev, Dimitri Ivanovitch (1 8 3 4 - 1 907), Russian chemist ; best known for his periodic system of classification of chemical elements in order of atomic weights, on the basis of which he was able to predict the properties of the elements then unknown. Moseley, Henry Gwyn Jeffreys ( 1 8 8 7 - 1 9 1 5), English physicist, known for his research on X-ray spectra of elements; discovered the law of atomic numbers of the elements . 226

Newton, Sir Isaac ( 1 642- 1 7 27), English math­ ematician and philosopher, developed the laws of gravitation and of motion; constructed the first reflecting telescope; cFedited with the in­ vention of the mathematical science called calculus. Oersted, Hans Christian ( 1 777- 1 8 5 1), Danish physicist, founded the science of electromag­ netism. Ohm, Georg Simon ( 1 7 8 7- 1 8 54), German physicist, discovered the relationship between the electromotive force and the resistance of a circuit, now known as Ohm's law. The practi­ cal unit of electrical resistance, the ohm , is named after him. Pascal, Blaise ( 1 623-1 662), French scientist and mathematician, experimented on equili­ brium of fluids and on differences in baromet­ ric pressure at different altitudes, known as Pascal's Law ; invented the hydraulic press. Planck, Max ( 1 8 5 8 - 1 947 ) , German physicist, originated and developed the quantum theory; known for his work in thermodynamics. Redi, Francesco ( 1 626- 1 698 ) . Italian physi­ cian; first to help disprove the theory of spon­ taneous generation by experimentation. Roentgen, Wilhelm ( 1 845- 1 923), German physicist, discovered X-rays, frequently called Roentgen rays. Rutherford, Ernest ( 1 8 7 1 - 1 937), British physi­ cist, investigated the nature of the atom ; dis­ covered the proton, alpha and beta particles, gamma rays and transmutation. Seaborg, Glenn (1 9 1 2), American physi­ cist, discovered many of the man-made ele­ ments called transuranium elements. Thomson, Sir Joseph ( 1 8 5 6- 1 940), English physicist, discovered the electron and investi­ gated its mass and charge. Volta, Alessandro ( 1 745-1 8 27), Italian physi­ cist, invented the electrophorus, the electro­ scope, the electrical condenser and the voltaic battery. He first advanced the theory that elec-

tricity is generated by the contact of unlike metals. The unit of electrical pressure, the "volt," is named after him.

Watt, James ( 1 73 6 - 1 8 1 9), Scottish inventor, made the modern steam engine practicable.

The "watt," the unit of electrical power, is named after him.

Wohler, Friedrich ( 1 800- 1 8 8 2), German chemist, fitst to synthesize an organic com­ pound (urea); founder of organic chemistry.

I M PO RTANT SC I E N T I F I C LAW S A N D P R I N C I P L ES Archimedes' Principle. A n object immersed in a fluid seems to lose weight and the apparent loss in weight is equal to the weight of fluid displaced. ( An object immersed in a fluid is buoyed up by a force equal to the weight of fluid displaced. ) Bernoulli's Principle. The pressure of a fluid (liquid or gas) decreases as the speed increases. Einstein's Formula. E = mc2• It states that en­ ergy, E, is equal to mass m, times the square of the velocity of light, c, in centimeters per second. Law of Charges. Unlike charges attract each other and like charges repel each other. Law of Conservation of Matter and Energy. Energy may be transformed from one form to another, but it cannot be created or de­ stroyed in ordinary chemical reactions. Law of Definite Proportions. Every compound has a definite composition by weight. Law of Gravitation. All bodies in the universe attract each other with a force that is directly proportional to the product of their masses and is inversely proportional to the square of the distance between them. Law of Illumination. The intensity of light varies directly as the candle power of the source and inversely as the square of the dis­ tance from the source.

Law of Machines. Under ideal conditions, the work output of any machine must theoretically equal the work input. Law of Magnetic Poles. Like magnetic poles will repel each other and unlike magnetic poles will attract each other. Law of Moments. When an object is in equilib­ rium the sum of the counterclockwise moments is equal to the sum of the clockwise moments. Law of Reflection. The angle of reflection is equal to the angle of incidence. Ohm's Law. The electrical current in amperes is directly proportional to the electromotive force in volts, and inversely proportional to the resistance in ohms. Pascal's Law. Pressure applied to a confined liquid is transmitted undiminished equally to all parts of the liquid and acts in all directions. Quantum Theory. Light is transmitted as elec­ tromagnetic waves consisting of tiny bundles of energy. Theory of Magnetism. Magnetic properties are related to the fact that the electrons in an atom spin on their own axis at the same time that they are orbiting the nucleus, thus producing magnetic fields. The atoms act as tiny magnets with all their north ( + ) poles facing one way and all their south ( - ) poles facing the oppo­ site way.

227

G LOSSARY absolute zero - the least amount of energy that an object can possess and, thus, the coldest pos­ sible temperature.

Angstrom (A) - the unit used for measuring the length of electromagnetic waves. ( 1 A = 1 0 - 8 cm .) 1 / 1 0,000 o f a micron.

acetylene series - a series of structurally related hydrocarbons with a general formula CnH�n - 2 .

antimatter - matter that . has charges opposite to all atomic particles.

acoustics - the study of sound.

applied science - the work of scientists who put the discoveries of pure researchers to practical use.

active element - an element whose outer ring is incomplete, and which tends to complete this outer orbit. actinide series (atomic numbers 90-103) - rare earth elements. activity series - a table of metals or non-metals arranged in order of descending activity. adhesion - the attractive force between unlike molecules.

armature - a large coil of wire in an AC genera­ tor which is wound around a soft iron core mounted on an axle which permits it to rotate in the magnetic field. aromatic compounds - compounds of the ben­ zene series. artificial magnet - a magnet made by man from iron or steel .

adsorbing agent - a substance which attracts and holds other substances to its surface.

astrophysics - the study of the physical laws re­ lating to space and the heavenly bodies.

aeration - spraying filtered water into the air to remove odors, kill bacteria, and eliminate bad­ tasting gases.

atom - the smallest part of an element that pos­ sesses all the properties of that element and that can enter into a chemical reaction.

aeronautics - the design and construction of air­ planes and rockets.

atomic fallout - odorless, tasteless and often in­ visible dust and dirt contaminated with radio­ activity as the result of a nuclear explosion.

alloys - a metallic substance formed when two or more metals are melted together. alternating current (AC) - electrical current which constantly reverses its direction of flow. alpha particles ( a ) - high speed helium nuclei each of which is composed of two protons and two neutrons; they have a positive charge and very little penetrating power. ammeter - an instrument used to measure the rate of flow of an electric current. ampere (A) - the unit used to measure the rate of flow of an electric current. amplitude - the maximum distance which a particle in a wave moves from its point of origin. angle of incidence - the angle between the nor­ mal and the incident ray. angle of reflection - the angle between the nor­ mal and the reflected ray. 228

atomic fission - the process of splitting the nu­ cleus of an atom, thus releasing energy. atomic fusion - the uniting of the nuclei of light atoms under conditions of extreme heat to form elements of greater atomic weight. atomic number - the number of positively charged protons in the nucleus of an atom; shows the position of an element in the Periodic Table of Elements. atomic pile - a type of atomic furnace. atomic weight - the weight of an atom equal to the sum of the protons and neutrons in its nu­ cleus. automotive engines - mechanical devices for transforming the chemical energy of fuels into mechanical or heat energy. balance - instrument which determines the weight of an object by comparing the unknown mass with the weight of a known mass.

-

an instrument used to measure pres­

bustle pipe the huge pipe filled with preheated air that circles the base of a blast furnace.

base a chemical compound which yields hy­ droxyl ions in a water solution.

caissons devices in which men can work under water to construct foundations for bridges and tunnels.

barometer sure.

-

-

-

basic oxygen furnace a furnace in which pure oxygen is blown at high speed above the molten iron to oxidize out impurities in the production of steel. -

bells structures in a blast furnace which pre­ vent loss of heat. -

benzene series a unique series of structurally related hydrocarbons in which the carbon atoms are united in a hexagonal ring; its general formula is C6 He. -

Bessemer converter an egg-shaped furnace in which iron is converted into steel by blasts of air which blow out impurities. -

beta particles «(3) negatively charged electrons with speed equal to the speed of light and greater penetrating power than alpha particles.

-

-

calorie the amount of heat needed to raise the temperature of one gram of water 1 0 C. -

calorimeter an instrument for measuring the number of calories of heat present in foods and other materials. -

candle power (CP) the unit for measuring the rate at which light is emitted. -

capillary action the attraction between the walls of a thin tube and the liquid it contains which causes the liquid to rise up the tube. -

carbon black the soot produced by the incom­ plete combustion of natural gas. -

cast iron a softer form of iron made from melted pig iron mixed with scrap iron. -

biophysics the study of the physical laws re­ lating to the activities of living organisms.

catalyst a substance that speeds up chemical reactions without itself undergoing any permanent change or being used up.

blast ( atomic bomb ) - the destructive force of a nuclear explosion, measured in kilotons or mega­ tons.

Celcius or Centigrade scale a scale used to ex­ press temperature in degrees; boiling point of water is 1 000 c., and the freezing point is 00 C.

-

-

blast furnace a huge furnace in which iron is separated from iron ore. -

boiling heating of water at the boiling point long enough to destroy most harmful germs; the rapid vaporization of liquids. -

boneblack animal charcoal made by the de­ structive distillation of bones. -

breeder reactor a special type of nuclear re­ actor which produces more atomic fuel than it consumes. -

British thermal units (B.T.V.) The amount of heat necessary to raise the temperature of one pound of water 1 0 F. -

Brownian movement the erratic, zigzag motion of particles in a conoidal suspension. -

brushes devices made of carbon or metal which conduct the current from the slip rings of an AC generator or the split ring of a DC generator to wires which then carry the electricity to the ex­ ternal circuit. -

buoyancy the upward force exerted by a liquid or gas on an immersed or floating object.

-

centimeter tem.

-

1/ I 00 of a meter in the metric sys­ -

centrifugal force a force acting on a revolving body which exerts a pull away from the center of revolution. -

centrifuge a device for separating materials from solution by whirling the solution at high speed. -

centripetal force the force required to keep an object moving in a circular orbit. -

chain reaction a nuclear reaction in which the splitting of the atomic nuclei releases enough neu­ trons to make the reaction continue until all the fissionable material is used up. -

charcoal the product formed by the destructive distillation of wood, used as an adsorbing agent and as fuel. -

charge the raw materials consisting of a mix­ ture of iron ore, coke and limestone used in a furnace in the process of iron ore reduction. checker chambers areas below the hearth of an open-hearth furnace for heating the air used in the production of steel. -

229

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chemical change a change in which new sub­ stances with new properties are formed. -

chemical energy the heat that comes from the oxidation of digested food, and from the burning of fuels. -

chemical indicators chemicals which indicate whether a solution is an acid or a base by their change in color. -

chemical properties the characteristics of mat­ ter that describe its reaction when it combines chemically with another substance. -

chemistry the study of the composition of mat­ ter and the chemical changes taking place in mat­ ter. -

chlorination the adding of chlorine compounds to water to kill harmful bacteria. -

coagulation a process for purifying water by adding chemicals such as alum or lime which clump fine particles together which then settle to the bottom. -

coal the result of the slow chemical breakdown of plant remains subjected to great heat and pres­ sure over a very long period of time. -

cohesion the force of attraction between similar molecules that holds matter together. -

coke the product made by heating bituminous coal in the absence of air. -

colloidal suspension a special kind of suspen­ sion composed of particles intermediate in size be­ tween those of a solution and a suspension which are so small they never settle out. -

combination reaction the chemical union of two or more elements to form a single compound. -

commutator the single split ring in a direct cur­ rent generator that reverses the direction of an electric current, thus changing alternating to direct current. -

components the separate forces that combined make up a single resultant force. -

compression the part of a sound wave in which air particles are squeezed close together ahead of the forward vibration of other particles. -

compound a chemical combination of two or more different kinds of elements in definite pro­ portions by weight. The resulting substance is dif­ ferent from the elements from which it was made. -

compound machines devices made up of two or more simple machines which together do a specific job. 230

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concave lens a piece of glass that is thinner in the middle than at its edges and causes light rays to diverge. -

concentrated solution a solution containing a large amount of solute to be dissolved in a small amount of solvent. -

concurrent forces two or more forces acting upon an object at the same time. -

conduction the transfer of heat from one mole­ cule of a solid to the next through molecular col­ lisions. -

conductor any material that permits electrons to flow easily through it. -

control a scientific procedure in an experiment in which no variable is present. -

control rods rods containing boron or cadmium which are placed in a nuclear reactor to absorb free neutrons and thus control the rate of fission. -

controlled experiment a scientific experiment in which two procedures identical in every way ex­ cept one are followed. -

convection the transferring of heat by a group of molecules which produce a current in liquids and gases until the same temperature exists throughout the fluid. convex lens the middle.

-

a piece of glass that is thickest in -

convalent bond the strong bond that holds ele­ ments together when they share electrons. -

covalent compound the compound which re­ sults when electrons are shared between two or more atoms . -

cracking the decomposition of large hydrogen molecules such as those found in fuel oils into the simpler, more volatile molecules of gasoline. -

crest wave.

the peak of an electromagnetic or sound -

critical mass the amount of nuclear fuel neces­ sary to bring about a chain reaction. -

cryogenic temperatures extremely low tempera­ tures beginning at - 1 50° F. cryogenics tures.

-

the study of extremely low tempera­

-

crystal the solid formed by groups of ions ar­ ranged in a definite pattern. current electricity a flow of electrons through a conductor; "electricity in motion." -

decibel - the unit used to measure the loudness of sound. decomposition reaction - the breaking down of a compound into simpler compounds or into its ele­ ments. density - the weight ( mass ) of a unit volume W ( weight ) . of matter. D (densit y) = V (volume) diamond - the hardest known natural substance, considered precious because of its rarity and its ability to reflect and refract light to produce a bril­ liant sparkle. diffused light - scattered light rays reflected from a rough surface. diffusion - the uniform distribution of a gas t6 fill all available space. Also, the bouncing back in all directions of rays of light which strike a rough surface. dilute solution - a solution containing a large amount of solvent and a small amount of solute. dipoles - atoms that behave like tiny magnets if their magnetic fields are not neutralized. direct current (DC) - electric current in which the electrons flow in one direction only.

dynamo - machine which transforms mechanical energy to electrical energy. echo - the reflection of sound waves.

efficiency - the ratio between the ouput of use­ ful work and the total work input expressed as a Work Output . percent. EffiCIency = X 1 00 % Work Input effort - the applied force exerted to overcome the resistance. effort arm (EA) - the distance from the point at which the effort is applied by a lever to the ful­ crum. electric furnace - It furnace which uses high volt­ age current to melt the charge in the production of steel alloys. electric motors - devices that transform electrical energy into mechanical energy. electrical power - the rate at which electrical en­ ergy is converted to work. Electrochemical series - see Activity Series of Metals. electrolytes - fluids that contain charged atoms ( ions ) and can conduct an electric current.

dispersion - the separation of white light into a spectrum of six different colors.

electromagnet - a temporary magnet made of an insulated wire wound around a soft iron core and connected to a source of electrical energy.

displacement - the volume of water moved from its original position by an object immersed in a fluid.

electromagnetic spectrum - the composite of all electromagnetic waves arranged by frequency and wave length.

dissociation - see ionization. distillation - the method of removing impurities from fluids by boiling, evaporating and condens­ ing the water vapor. domains - magnetic regions in which dipoles are arranged with their north poles all facing in one direction and their south poles in the opposite direction. dose rate meter - an instrument used to measure levels of existing radiation. dosimeter - an instrument used to measure the amount of accumulated radioactivity. double replacement reaction - the chemical re­ action of two compounds in which they exchange places, forming two new compounds. drag - the force that opposes the thrust of an air­ plane in flight and tends to slow down its forward motion.

electromagnetic waves - a transverse wave pos­ sessing both electrical and magnetic properties. Electromotive Series - see Activity Series of Metals. electl'on - a negatively charged particle found around the nucleus of the atom. electronics - the design and construction of TV, radio, radar, etc. electl'on microscope - an instrument using a beam of electrons to magnify up to 500,000 times structures so small they cannot be seen with an ordinary microscope. electronegative elements (-) - non-metallic ele­ ments which borrow electrons during a chemical reaction. electropositive elements (+ ) - elements which lose electrons during a chemical reaction. 231

-

electroscope a device used to detect static elec­ trical charges. electrostatic compound

-

-

see ionic compound.

electrostatic precipitators (Cottrell Precipitators) devices which give particles in smoke and dust an electrical charge and then collect the particles at an electrode having an opposite charge in order to free the air of polluting particles.

-

-

electrovalence

see ionic compound.

-

element a substance which cannot be broken down into simpler substances by ordinary chemical means. -

endothermic reactions chemical which energy is absorbed. energy

-

changes

in

the ability to do work. -

energy level the position of an electron in orbit around the nucleus of an atom. -

equation the chemist's shorthand way of de­ scribing the substances reacting and the products formed during a chemical reaction. -

equilibrant a single force equal but opposite in direction to a resultant. -

equilibrium the state of balance when opposing forces are acting equally on an object. -

ethylene series a series of structurally related hydrocarbons with a general formula Cn H"" . evaporation vapor.

-

process of changing a liquid into a -

exothermic reactions chemical changes which result in the release of heat energy. -

experiment a scientific procedure containing a control and a variable to test an idea. -

exposure meter a device used in photography for measuring the intensity of available light. -

external combustion engine a heat engine i n which fuel i s burned outside the chamber or cylin­ der. extraction -

fact true.

-

the separation of metal from its ore.

information that has been proved to be -

Fahrenheit scale a scale used to express tem­ perature in degrees ; boiling point of pure water is 2 1 2 oF., and freezing point is 32 oF. -

fallout shelter a protected area constructed as defense against atomic fallout.

232

-

field magnets magnets with opposite poles in an AC generator which provide the magnetic field. filtration the process of purifying water by passing the water through sand and gravel to re­ move suspended solids. -

firebrick the lining of a blast furnace which can withstand extremely high temperatures. -

first-class lever a lever in which the resistance is at one end and the effort at the other with the fulcrum somewhere between the two. fission ftux

-

-

see atomic fission.

a material which removes impurities. -

focal length the distance from a lens to the point where parallel rays converge. -

foot-candle unit for measuring the intensity of light per square foot. -

foot-pound the measure of work done by a one­ pound force moving an object a distance of one foot. -

force any push or pull which can produce, pre­ vent or stop motion. -

formula the chemist's shorthand for a com­ pound which tells the elements and number of atoms it contains. formula weight

-

see molecular weight. -

fractional distillation the process by which use­ ful hydrocarbons are separated from petroleum. -

fractionating tower the tall tower in which vapors and the liquid not vaporized are collected in the process of heating crude oil in a furnace. -

frequency the number of complete vibrations made by a vibrating object in one second. -

friction the resistance of one body to the move­ ment of another body along its surface. -

fulcrum the pivot point on which a lever is sup­ ported and is free to rotate. -

fundamental the lowest tone produced by a wire vibrating in one part. fusion

-

see atomic fusion. -

galvanometer a sensitive instrument used to measure the strength of weak electric current. gamma rays (y) very high energy X-rays having no electrical charge and great penetrating power. -

gas - a state of matter which has no definite vol­ ume or shape.

hydrocarbons - organic compounds containing only carbon and hydrogen atoms.

generator - a device that converts mechanical en­ ergy into electrical energy.

hydrometer - an instrument used to determine the specific gravity of liquids.

geophysics - the study of the physical l aws re­ lating to the structure and activities of the earth.

hypothesis - a possible solution to a problem; an "educated guess."

gravitation - a force of attraction which every­ thing in the universe has.

illuminated objects - those which are visible be­ cause of the light they reflect.

gravity - the force of gravitation near the earth and other planetary objects.

incident ray - the ray of light that strikes an object.

gram - the basic unit of weight in the metric sys­ tem; approximately 454 grams equal one pound.

inclined plane - a simple device used to reduce the effort needed to move an object.

graphite - a soft form of carbon used in lead pen­ cils, lubricants and crucibles.

index of refraction - the ratio of the velocity of light in air or a vacuum to the velocity in another substance.

groups (families) - the vertical arrangement of elements in the Periodic Table that have similar properties. gyro-compass - a gyroscope that spins always in a north-south direction and is not affected by metals as other compasses are. gyroscope - a device which is a wheel spinning like a top ; it resists being turned and stays level at all times.

induced current - the electric current produced in a conductor of a closed circuit when the con­ ductor cuts the lines of force of a magnetic field. inert element - an element whose outer ring con­ tains the maximum number of electrons it can hold. inertia - the tendency of an object to remain at rest or in motion because of its mass.

half-life - the length of time required for half the atoms of a radioactive element to disintegrate.

ingot molds - huge forms into which molten steel is poured to cool and solidify.

Halogen family - a group of very active non­ metals .

insulator - any material that does not permit electrons to flow readily through it.

hard (anthracite) coal - the purer form of carbon resulting from plant decomposition accompanied by great heat and pressure.

internal combustion engine - a heat engine in which fuel is burned within a chamber or cylinder.

hard water - water which contains dissolved min­ eral matter that interferes with the sudsing of soap and forms a visible scum. hearth - the huge basin at the bottom of a blast furnace in which molten iron and waste collect. heat - a form of radiant energy which is ab­ sorbed, emitted or transferred between objects of different temperatures ; the energy of molecules in motion. horsepower - the unit of measure of the power developed by machines. 1 HP = 3 3 ,000 ft-Ib. of work done in 1 minute or 5 50 ft.-lb. per second . hydrates - crystalline compounds formed by the union of certain substances with water in definite proportion by weight. hydraulic machines - devices that transmit force by means of liquids.

ionic compound - a chemical union of oppositely charged ions. ions - atoms or radicals that have gained or lost electrons and have become either positively or negatively charged. ionization - the process by which the molecules of certain compounds break up when dissolved in water and set free charged particles. isomer - a compound whose molecules contain the same number and kinds of atoms as the orig­ inal element but in different arrangement. isotope - a different form of an element having the same atomic number and chemical properties but a different atomic weight. Kelvin scale - a scale used to express the lowest possible temperature reading of -459.69 °P. or -27 3 . 1 6°C. which represents absolute zero. 233

kiloton - a unit equal to 1 ,000 tons. kilowatt - a unit for measuring electrical energy ; 1 kilowatt = 1 000 watts. kinetic energy - the active energy possessed by an object because of its motion. lamp black - soot produced when fuels with high carbon content are incompletely burned. lanthanide series (atomic numbers 58-71) - ele­ ments listed separately at the bottom of the Peri­ odic Table because of their similar properties. latex - the milky, elastic sap of the rubber tree. lever - a simple machine consisting of a rigid bar supported at a fixed point around which the lever can turn. lift - the force that acts on the wings of an air­ plane in flight to overcome the pull of gravity. light - a form of electromagnetic radiation visible to the eye. light meter - a device used in photography to measure the intensity of available light. light microscope - an instrument used to magnify up to 2000 times tiny structures that would other­ wise be invisible to the unaided eye.

lumen - a unit for measuring the intensity of light. mach 1 - the velocity of sound milhr. )

10

air (74 1

machine - a device for doing work more easily and more quickly. mass - the quantity of matter contained in an object. magnetic field - the area surrounding a magnet in which its magnetic effects are found. magnetic permeability - the ability of substances to allow magnetic lines of force to enter easily. magnitude - the size or amount of a quantity being measured. manometer - an instrument used to measure small pressures. matter - anything that occupies space and has mass. mechanical advantage (MA) - the number of times that a machine multiplies the effort force ap­ plied to the machine.

light year - the distance light travels in one year - about 6 trillion miles.

mechanical energy - the heat that results from friction and the mechanical compression of mole­ cules.

lines of force - the invisible pattern of magnetic effects concentrated at the opposite poles of a magnet.

megaton - a unit equal to 1 ,000,000 tons of TNT used to measure the force of a nuclear blast.

liquid - a state of matter which has a definite volume but no definite shape. liquid pressure - force exerted by a liquid de­ pending on its density and its depth. liter - the basic unit of volume in the metric system ; it is equal to 1 .06 quarts. litmus - red and blue dyes derived from a plant extract and used as a chemical indicator. lodestone - a natural magnet. longitudinal waves - a wave such as a sound wave, in which the molecules vibrate forward and back­ ward parallel to the direction in which the wave is traveling.

meniscus - the curved surface of a liquid within a container caused by the differences in cohesive and adhesive forces. metal - an element whose atoms lend electrons, is usually a solid at room temperatures, conducts heat and electricity well, has high density, and can easily be hammered or shaped. metallurgy - the science of separating a metal from its are and removing unwanted impurities. meter - the basic unit of length in the metric sys­ tem; it is equal to 39.37 inches.

loudness of sound - the quality of sound that de­ pends upon the amplitude of the sound wave.

methane (CH2) - a gas - the simplest hydro­ carbon having only one carbon atom and two hy­ drogen atoms; the first of a series of hydrocarbons also called the "paraffin series."

luminous objects - those which emit their own light.

metric system - a system of measurement based on multiples of ten.

234

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mixture a combination of two or more sub­ stances each of which substance retains its original properties. -

moderator a material used to slow down the fast neutrons that are freed in atomic fission. -

molecular forces the gravitational and electrical forces that attract molecules to each other. -

molecular weight the sum of all the atomic weights of all the atoms comprising a specific molecule. -

molecule the smallest particle of a substance having the properties of the substance. -

moment of force the product of the force and the perpendicular distance from its point of appli­ cation to the fulcrum. -

monomers the simple starting molecules which are joined together in the process of polymeriza­ tion. -

mutation a new trait, often harmful, brought about by damage to the reproductive cells that control heredity. native metals

-

metals found in the free state. -

natural elements the 92 elements found in na­ ture ; those not made by man. -

negative pole (south pole) the end of the mag­ net that always points toward the earth's south. magnetic pole. -

neutralization the reaction between an acid and a base to produce water and a salt. -

neutron a particle in the nucleus of an atom having no electrical charge. -

non-metal an element whose atoms borrow electrons, is usually a poor conductor of heat and electricity, has low density and may have a char­ acteristic color. -

normal the line drawn perpendicular to the sur­ face at the point where the incident ray strikes. nuclear or atomic energy the energy, including heat, that results from nuclear reactions. -

-

nuclear physics the study of the physical laws relating to nuclear structure and the activities of atoms. nuclear reactor a type of atomic furnace which harnesses the energy obtained from a controlled chain reaction of nuclear fuel. nucleus the central part of the atom. ohm ({2) the unit used to measure the amount of resistance to the flow of electricity. -

-

-

-

opaque objects those that prevent light rays from passing through them. open-hearth furnace ducing steel.

-

a large furnace for pro­

-

optics the design and construction of instru­ ments using lenses. -

orbit the path of an electron around the nu­ cleus of an atom. -

ore a mineral ( chemical compound ) from which a metal or non-metal can be extracted profitably. -

organic chemistry the branch of chemistry con­ cerned with the study of compounds containing carbon. -

parallel circuit an electric circuit in which the electrons may flow through the different paths of the circuit. -

particle accelerators machines which accelerate atomic bullets, to smash atoms, create synthetic elements and investigate atomic structure. -

peat vegetation which has undergone partial decomposition under water. -

Periodic Table of the Elements the orderly ar­ rangement of the elements based on their atomic structure. -

periods the horizontal row of elements in the Periodic Table. -

permanent hard water water containing calcium or magnesium salts which cannot be removed by boiling. -

permanent magnet a magnet made of steel or a steel alloy that retains its magnetic properties for a long time. phenolphthalein it chemical indicator which is colorless in an acid solution and turns dark pink when a base is present. -

-

photocell electricity.

photometry

a device which converts light into

-

the science of measuring light.

-

photons bundles of energy which make up the electromagnetic waves of light. -

pH scale a numerical scale used to measure the strengths of acids and bases. -

physical change a change in the form of matter which does not produce a new substance. -

physical properties the properties of matter that can be identified by the senses. 235

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physicist a scientist who deals with the laws governing the activities of our physical world. -

physics the science that deals with matter and energy and their interrelationship. -

pig iron the hard, brittle, impure form of iron produced in a blast furnace. -

pitch of sound the high or low quality of sound that depends upon the high or low frequency of the sound wave. plasma

-

the liquid part of the blood.

-

plastics complex organic compounds which can be easily shaped by heat or pressure. -

polar (or dipolar) molecules molecules having a negative and a positive charge. -

polarized light light which vibrates in one plane rather than in all directions. -

pollution the spoiling of the limited fresh water supply by dumping of industrial and community wastes. -

polymer the large, complex molecules which re­ sult from the joining of simple monomers in the process of polymerization. -

polymerization the process in which small molecules called monomers are combined to form large or giant molecules. -

positive pole (north pole) the end of the magnet that always points to the earth's magnetic pole which is near the earth's geographic north pole. -

potential energy the stored energy that an ob­ ject has because of its position or condition. -

power the measure of the rate of time at which work is done. -

pressure the force exerted on a unit area of a given surface. -

protective shielding a concrete shield used as protection against dangerous gamma rays radiated during atomic fission. -

principal focus the point at which parallel light rays refracted through a convex lens converge. -

proton a positively charged particle in the nu­ cleus of the atom. protoplasm -

-

the living material of a cell.

pulley a simple machine having one or more fixed or movable wheels, used to lift heavy ob­ jects. 236

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pure or basic science the work of the scientist who searches for answers to questions without par­ ticular interest in immediate useful applications. -

quantums bundles of energy which make up the electromagnetic waves of light. -

quantum theory the theory that light is trans­ mitted as electromagnetic waves consisting of tiny bundles of energy. -

radiant energy magnetic waves.

energy transmitted by electro­

-

radiation the transfer of energy, including heat, as electromagnetic waves. -

radicals groups of two or more atoms that be­ have as a single unit. -

radioactivity the spontaneous disintegration of an unstable nucleus which gives off radiation in the form of alpha and beta particles and gamma rays. -

radioisotope an isotope that is radioactive; that is, its nucleus is constantly breaking apart, releas­ ing energy and, in the process, forming new sim­ pler elements. -

radio telescope an astronomical instrument like a huge antenna that collects radio waves from outer space. -

rarefaction the part of a sound wave in which air molecules are pushed farther apart as they vibrate backward. -

reduction the removal of oxygen from iron ore at high temperatures. -

refining the removing of unwanted impurities from extracted metal. reflected ray a surface.

-

the ray of light that rebounds from -

reflecting telescope an astronomical instrument that uses mirrors to collect and direct light rays to a single lens. -

refracting telescope an astronomical i nstrument that uses two convex lenses. -

refraction the bending of light resulting from the difference in the speed of light in media of different optical densities. -

resistance the force which must be overcome in doing work, or the opposition of a substance to the flow of electrons. -

resistance arm (RA) the distance from the point where the resistance of a lever acts to the fulcrum.

-

resolution of a force the determination of the components of a single force. -

resultant a single force that can replace two or more forces acting upon the same point and produce the same result. ring

-

-

rotors moving field magnets in huge industrial AC generators. -

rubber a polymer consisting of several thou­ sand molecules of the hydrocarbon monomer iso­ prene (C5 Hs ) . -

saturated solution a solution in which the sol­ vent has dissolved all the solutes it can at a given temperature and pressure. -

the completion of the outer ring of

scalar quantities - quantities magnitude.

possessing only

-

scientific law the result of consistent observa­ tion of certain effects without exception, yet for which no satisfactory explanation is available. -

scientific method a planned, orderly procedure applied to solving a problem to produce facts and accurate evidence to support a conclusion. -

screw a circular inclined plane wrapped around a cylinder, the use of which can overcome a large resistance with a small force. -

second-class lever a lever in which the fulcrum and the effort are on opposite sides with the re­ sistance located between the fulcrum and the ef­ fort. -

sedimentation a process for purifying water by collecting water in reservoirs or settling basins and allowing solid particles to settle to the bottom. -

semiconductors substances that behave as con­ ductors or as insulators depending upon such con­ ditions as temperature. -

series circuit an electric circuit in which the electrons follow a single path leaving one termi­ nal of source. shell

-

see orbit. -

silicones organic compounds, the molecules of which contain silicon atoms as well as carbon atoms. simple machines few parts.

-

skip cars rail cars which carry the charge mix­ ture to the top of a blast furnace. -

see orbit.

saturation an atom.

-

single replacement reaction the reaction of a chemically more active element with a compound to replace a less active element in the compound.

-

devices that have only one or

slag the waste product formed when limestone is used to remove impurities from iron. -

slip rings insulated brass rings connected to the armature of an AC generator which conduct current from the armature to the brushes. -

slug an aluminum tube in which nuclear fuel is inserted into an atomic pile. -

soft (bituminous) coal the product resulting from plant decay, heat and pressure. soft water mineral.

-

water containing very little dissolved

-

solid a state of matter which has a definite shape and volume. solubility solved. solute

-

solution solute.

-

the dissolved substance in a solution.

-

-

solvent stances.

the ability of a substance to be dis­

a uniform mixture of a solvent and a

a substance that dissolves other sub­

-

sonar the equipment used for the reception and interpretation of ultrasonic vibrations reflected by underwater objects. -

sonic barrier a barrier of dense air in front of an airplane which the plane must pass through when it approaches the speed of sound. -

sound the transmission of the vibration of molecules to the ear. -

sound waves the travel pattern of vibrations through the transmitting medium. -

specific gravity (specific weight) the ratio of the density of a substance compared to a stand­ ard reference - water for liquids and solids, air for most gases. -

specific heat the property of water to absorb or radiate large amounts of heat without changing its own temperature. -

spectroscope an instrument used to determine the elements present in a luminous object or a mass of burning gas. speed of light

-

1 86,000 miles per second. 237

-

spherical photometer an instrument for measur­ ing the light intensity of various light sources. -

standard candle a specific type of candle used as the standard of comparison in measuring the rate at which light is emitted. -

static electricity the momentary transfer of electrons between unlike materials resulting from friction or contact; "electricity at rest. " -

stators stationary armatures i n huge industrial AC generators around which the field magnets rotate. -

steel refined pig iron from which much of the carbon impurity has been removed. -

stoves cylindrical stoves that preheat the air that enters the blast furnace. --

subscript the small number written below and to the side of a symbol. When at the left it repre­ sents the atomic number ; at the right it represents the number of atoms in an element. -

subsurface burst a nuclear explosion that takes place underground. -

superconductors certain metals which become good conductors in that they offer no resistance to the flow of current at very low temperatures. -

supersaturated solution a solution which con­ tains more dissolved solute than it could normally hold at a given temperature and pressure. -

surface burst a nuclear explosion which takes place above ground. -

surface tension a characteristic of a liquid which causes its surface to behave as though it were a thin plastic "skin." -

suspension a non-uniform mixture of tiny, in­ soluble solid particles distributed in a liquid or gas which settle out on standing and can be re­ moved by filtration. -

symbols the chemist's abbreviations for the names of elements. synthesis reaction

-

synthetic elements synthetic textiles fibers.

see combination reaction.

-

-

man-made elements.

fabrics made from synthetic

-

taconite low-grade magnetite ore found in the Mesabi Range. -

telescope an instrument used by astronomers to bring far distant objects into view. 238

-

temporary hard water water containing calcium or magnesium salts in solution which can be re­ moved by boiling. -

temporary magnet a magnet made of soft iron that retains its magnetic properties for a short time. -

temperature a measure of the degree of heat or cold of an object that depends upon the speed with which its molecules are moving. theory a scientific explanation for a phenome­ non that has been accepted for a rather long pe­ riod of time, but has not been proved true. -

-

theory of magnetism a scientific belief that magnetic properties are related to the fact that the electrons in an atom spin on their own axis at the same time that they are orbiting the nucleus, thus producing magnetic fields. -

thermocouple a device that produces electricity by joining two different metals together so that there is a temperature difference between the two junctions. -

thermodynamics the study of the relationship between heat and work. -

thermonuclear reaction the use of tremendously high temperatures to bring about atomic fusion. -

thermoplastic plastics plastics which can be softened by heat and reshaped after formation. -

thermosetting plastics plastics which, after for­ mation, cannot be softened by further heat treat­ ment. -

thermostat a device containing two strips of different metals which expand unequally with changes in temperature, used to complete an elec­ tric circuit for starting electric apparatus. -

thrust the force supplied by propellors or jets that propels a plane forward. -

third-class lever a lever in which the fulcrum and the resistance are at opposite ends with the effort located between the fulcrum and the resist­ ance. -

transformer a device for raising or lowering the voltage of alternating current. -

translucent objects those that allow light to penetrate them, but scatter the light making see­ ing through them difficult. -

transmutation the process of changing elements into other elements or producing new elements that will have atomic numbers that differ from the original by changing the number of protons in the nucleus of the atom.

transparent objects - those that transmit light readily, allowing objects to be seen easily through them . transuranium elements - synthetic elements heav­ ier than uranium and possessing higher atomic numbers. transverse wave - the path of light in space. The particles of energy being transmitted vibrate at right angles to the direction of the wave motion. turbine - an engine powered by steam, water or gas, that is turned by means of a wheel fitted with curved blades. tuyeres - small pipes that permit blasts of hot air to enter the blast furnace. ultrasonic vibrations - sound vibrations that travel faster than 20,000 vibrations per second. underwater bursts - a nuclear explosion in which radioactive water particles are formed. universal solvent - water, which dissolves more substances than any other solvent. valence - the number of electrons which an atom will lend, borrow or share in bonding with one or more atoms during a chemical reaction. valence bond - a single line ( -) or two dots ( ) used to represent a covalent bond. •

•

valence electrons - the electrons in the outer ring of an atom. Van de Graaf generators - devices which pro­ duce large static charges for use in atomic re­ search and for the production of high voltage for X-ray machines. vaporization - the process in which molecules of liquid receive enough energy through boiling to break away from the liquid and form a gas. variable - a difference in method that is followed in one of the two otherwise identical procedures in a controlled experiment. vector - an arrow which represents the direction of a force upon an object; the tail shows the , point where the force is applied, the head repre­ sents the direction of the force upon the object,

the length of the arrow represents the magnitude of the force. velocity of Iigbt - 1 86,000 miles per second. velocity of sound - the speed of sound which de­ pends upon the medium it passes through and the temperature. Venturi tube -- a narrow tube section of a larger pipe that operates upon the fact that as the ve­ locity of flow of a liquid or gas increases in the narrow section, the pressure decreases. volt (V) - the unit used to measure the force or pressure which pushes electrons through a con­ ductor. voltage drop - the decrease in voltage as the volt­ age travels across the various electrical resistances in a series circuit. vulcanization - the heating of sulfur and raw rub­ ber to make the rubber elastic and strong. watt (w) - the unit used to express electrical power. Power in watts = volts X amperes. wave length - the distance from a point on one wave to the corresponding point on the next wave. wedge - a double inclined plane to which a greater force must be applied to overcome a greater resistance. weight - the measure of the earth's gravitational pull on the mass of an object. wheel and axle - a device consisting of a wheel attached to a small circular axle. Force is applied to the outer edge of the wheel and resistance is attached to the axle. work - the exertion of a force through a dis­ tance to overcome resistance. W (work) = F (force) X D ( distance ) . wrought iron - a pure form of iron made from pig iron by removing many of the impurities. X-rays - rays that are similar to light or radio waves but have a much shorter wave length and a much higher frequency.

239

I N D EX atom smashers: betatron, beva­

A absolute zero, 1 1 0 absorption of light, 1 0 1 acetylene series, 2 1 0 acceleration,

62;

negative (de-

celeration), 62

face, un derwater, damage caused by, 1 27 bustle pipe, 1 9 9 butane, 2 1 0 butyl rubber, 2 1 9

1 30 atomic disintegration, 1 1 9 atomic energy, 1 09

AC generator, 83-84 acids, bases and salts, 1 9 1 - 1 9 8 ; properties, 1 9 1 - 1 92 , 1 94; com­ mon industrial and laboratory, common 1 92 ; 192 acoustics, 9 3

tron, cyclotron, megatron, synchrotron, 1 2 1 atomic attack, warnings against,

household,

actinide series, 1 7 1 , 1 7 5 active elements, 1 5 6 Activity Series o f Metals, 1 6 1 adhesion, effects of, 22, 1 4 5 adsorbing agent, 208

atomic fission, 1 1 9 ; fusion, 1 1 9 atomic number, 1 3 8 , 1 5 5; range of in Periodic table, 1 7 1 atomic pile, 1 20

caissons, 42 Calder Hall atomic power plant, 1 20 calorie, small and large, 1 1 0 calorimeter, 1 1 0

atomic weight, 1 54- 1 55

cancer, caused by radioactivity,

auditory nerves, 94 average kinetic energy, 1 09 axle, and wheel, a simple ma­ chine, 3 6

1 29 candle power, unit of measure, 1 03 capillary action, 2 2 carbon, amorphous (non-crystal­ line), 208; compounds of, 209

B

airplane, forces acting on, 5556 aeration, 1 8 5

C

atomic fallout, 1 27

Bakelite, 2 1 8

carbon black, 209 carbon-14;

alkalis, 1 9 1 , 1 9 2

balance, to determine metric weight, 4, 1 5 , 1 9 barometers, aneroid, mercury, 4. 4 1 basement fallout shelter, 1 29- 1 3 0

alloys, 8 1 ; steel, table o f impor-

bases,

air speed, factors that affect lift-

ing force, 55 Alkali Metal Family, 1 7 3

tant, 202 alnico, used as magnet, 8 1 alpha, beta particles, 1 28 Alpha Centauri, nearest star to earth, 97 alternating current (AC), 83 ammeter, 7 1

191,

1 92- 1 9 3 ;

chemical

reaction between, and a salt, 1 94 basic oxygen furnace, 20 1 Becquerel, Henri, 1 1 9 benzene series, 2 1 0 Bernoulli's Principle, 55-56; devices that operate on, 56

amorphous carbon, 207, 208 ampere, unit of measure, 7 1

Bessemer converter, 20 1

amplitude, of a sound, 92

bevatron, atom smasher, 1 2 1

aneroid barometer, 4 angle of incidence, 1 0 1

biochemical

angle of reflection, 1 0 1

bituminous coal, 208

angstrom, unit of measurement of wave length, 99

blast furnace,

anhydrous, 1 82 anthracite coal, 208 antibiotics, 2 1 7 antifreeze, 1 1 3 , 1 8 3 anti-matter, 1 54 antioxidants, 2 1 9 applied science, 1 1 aqualung, 42 Archimedes' Principle, 5 1 , 5 2 armature, o f generator, 83 aromatic

compounds, 2 1 0

astrophysics, 1 1 atom, 69; splitting, 1 1 9 ; defini­ tion of, 1 45 ; chemistry and the, 1 5 3 - 1 60; structure, 1 5 3 1 54; particles, 1 5 3 - 1 54

240

217

charge of,

freely falling,

62;

cast iron, 20 1 catalyst, 1 8 1 Celsius scale, 1 1 0 Centigrade scale, 1 1 0; changing to Kelvin, 1 1 0 centiliter, metric measure, 1 4 centimeter, metric unit o f length, 12 centrifugal force, 2 1 centrifuge, 2 2

charge, of furnaces, 1 99 , 200,

200; tapping the, 200 blue whale, and buoyancy, 5 1 bodies,

carbonates, 207

chain reaction, 1 1 9 , 1 20 charcoal, how made, 208

biophysics, 1 1 1 99 ;

isotope

Chadwick, James, 1 1 9, 1 5 3

betatron, atom smasher, 1 2 1 research,

radioactive

of, 1 29

dis­

tance covered by moving, 62 boiling water for destruction of germs, 1 85 bonds, valence, covalent, 209 boneblack, 209 breeder reactors, 1 2 1 British thermal units, 1 1 0 Brownian movement, 1 84 brushes, carbon or metal, in generator, 8 3 buo�'ancy, 4 1 ; and specific grav­ ity, 5 1 -60 burette, 4 bursts, atomic, surface, subsur-

20 1 charges,

electric,

negative and

positive, 69 ; Law of, 69 chemical activity, 1 6 1 - 1 70 chemical advances, 2 1 7-223; in health, 2 1 7 ; in industry, 2 1 72 1 9 ; c o n s e rv a t i o n o f r e ­ sources, 2 1 9-220 chemical change, definition of, 1 45 chemical energy, 1 09 chemical indicators, 1 9 1 chemical property o f matter, 1 45 chemical

reactions,

types

of,

1 64- 1 65 chemistry, and the atom, 1 53 -

1 60 chemistry, introduction to, 1 3 71 44;

defined,

of, 1 3 7

1 3 7;

branches

chemistry, organic, 207 chlorination, at water, 1 8 5 circuits, series, 7 2 ; parallel, 7 3

Curie, Marie and Pierre, 1 1 9 current, electricity, 7 1 -74; in­

civil defense, 1 27- 1 3 6 coagulation, 1 8 5 coal, bituminous and anthracite, 208 cochlea, of ear, 94 coefficient of a formula, 1 64 cohesion, 22, 1 45 coke, how made, 200, 208 colloids, 1 84 color, of an object, 1 0 1

decaliter, unit of volume, 1 4 deceleration, law of, 62

components of a force, 24

common,

1 3 9;

major differ­

ences between mixture and, 1 3 9 ; and ions, 1 62- 1 63 ; cova­ lent, 1 63 ; of carbon, 209-210; comparison of organic and in­ organic, 2 1 0; aromatic or ring, 210 compressed air, 42 compression, part wave, 9 1 concave lens, 1 02

of

sound

concentrated solution, 1 8 3 conclusions, i n an experiment, 2 concurrent forces, balanced, 23 condensations, in sound, 92 condensing water vapor, 185

1 1 3,

conduction, heat transfer b y , 1 1 1 conductor, electrical, 7 1 ; sound, 91 conservation of resources, 2 1 9220 contact method

decibel, unit of measurement of sound, 93 deciliter, unit of volume, 1 4 decomposition, o f molecules, 1 45

some

of making

a

magnet, 8 2 control, in experiment, 2 control rods, in atomic pile, 1 2 1 controlled experiment, 2 convection, transfer of heat by, 111 conversion factors, in metric and English systems, 3, 1 6 convex lens, 1 02 core, of electromagnet, 8 2 cosmic rays, 99 Cottrell precipitator, 70 covalent bond, 209 covalent compounds, 1 63 cracking, process of, 2 1 8

decontamination, removal of radioactive fallout, 1 3 0 density, o f matter, 4 1 , 42; of water, 1 1 3 depth, factor in pressure on liq­ uids , 43 desalinization, 1 8 6

97, .

1 1 9;

electric motor, 84-85; furnace, 202 Electrical Charges, Law of, 69 electrical circuits, series, 72; par­ electrical energy, 1 09 electricity, 69-80; static, 69-70; current, 7 1 -7 4 electrification, defined, 69 Electrochemical Series of Metals, 161 electrolyte, 7 1 , 1 63 electrolytic solutions, 7 1 electromagnetic radiations, properties of, 9 8 electromagnetic spectrum, 98-99 electromagnetic waves, 97 electromagnets, 82; industrial uses of, 8 2 electromotive force (EMF), 7 1 ,

destructive distillation of coal, 208 diamond, 207; crystalline form of, 207; arrangement of car­ bon atoms in, 207 diesel engine, 1 09 diffused light, 10 1 diffusion, 1 46 dilute solution, 1 8 3 dipoles, in magnetic substances, 82

84 Electromotive Series of Metals, 161 electron microscope, 1 04 electronegative non-metals, 1 62 electrons, 69, 1 5 3 - 1 54; rings, shells, orbits, levels, 1 53 , 1 56; valence, 1 56 electronic structure, 1 55 electronics, science of, 1 1 electroplating, process of, 8 3 electropositive elements, 1 6 1

direct current (DC), 83 direction, of a force, 22 disintegration, spontaneous, 1 1 9 ; atomic, 1 1 9 dispersion of white light, 99 displacement, of water, 5 1 dissociation, process of, 1 63 distance, astronomical, 97; from source of radiation, 1 29 distillation, of water, 1 85 ; frac­ tional 2 1 7 DNA (deoxyribonucleic 217

11,

equation, 1 22, 146

allel, 73

D

decameter, unit of length, 1 2

commutator, i n D C generator, 84

compound machines, 3 1 compounds, 1 3 7, 1 39;

duced, 8 3 ; types of electrical, 8 3 ; alternating, direct, 83 cycle, coil, 84 cyclotron, atom smasher, 1 2 1

Einstein, Albert,

acid),

domains, i n magnetic substances, 82 dose rate meter, 1 30 dosimeter, 1 3 0 double replacement, 1 92 dynamo, 84

electroscope, 69 electrostatic precipitator, 70 electrovalence, a type of chemical union, 1 63 electrovalent substance, 1 63 elements, 1 3 7 - 1 3 9 ; natural, 1 3 71 3 8 ; synthetic, 1 3 8 ; in earth's crust, 1 3 8; transuranium, 1 3 8, 1 39 ; inert, active, 1 5 6 endothermic reaction, 147 energy, 1 1 , 29, 29;

kinetic,

147; potential, 29;

and power,

75; and matter, 1 45- 1 5 2 energy, heat, sources of, 1 09 energy levels, of electrons, 1 5 3 energy, radiant, 9 7 , 1 09 energy released during nuclear explosfon:

light,

blast,

heat,

radiation, 1 27- 1 2 8 English system o f measurement,

critical mass, 1 20 cryogenic temperatures, 7 1 , 1 1 0 crystal lattice, 1 64 crystalline form of carbon, 207208 crystalline form of carbon, 207

ear, parts of, in hearing sounds, 94

crystals, 1 63

effort, 32, 3 3 , 34

E

echoes, 9 3 efficiency, o f machines, 3 1

1 2, 4 1 equations, chemical, 1 64 equiIibrant, 24 equilibrium,

balanced,

concur-

rent forces producing, 23 ethylene series, 2 1 0 evaporation, 1 1 3 ; o f water, 1 8 5 exothermic reaction, 1 47

241

experiment, scientific , 2

generators, 70, 8 3 -84, 1 46

exposure meter, 1 0 3

geophysics, 1 1

inert

Goodyear, Charles, 2 1 9 graduated cylinder, 4 , 1 4

Inert Gases, Family of, 1 7 3

external combustion engines, 1 09 extraction, process of, 1 99

2 1 7- 2 1 9

graphite, arrangement o f carbonates in, 208 gravitational force, 1 9 ; responsi­

F fact, defined, 3 Fahrenheit scale, 1 1 0 fallout, atomic, 1 27 families, in Periodic table, 1 7 1 , 1 72 , 1 7 3

ble for weight, 1 9 gravity, law of, 1 9, 29; center of, 19 gyroscope, 20

Family o f Inert Gases, 1 72, 1 7 3 correction

farsightedness, lenses, 1 02

with

field magnets, in generator, 8 3 filtration, 1 8 5 first

aid,

for

acid

burns, vii fission, nuclear,

and

1 1 9;

alkali

reaction,

1 27 fissionable material, 1 20 Flotation, Law of, 5 1 fluids, pressure in, 4 1 -50, 5 1

1 29 ; rate of decay, 1 7 3 Halogen Activity Series, 1 62 Halogen Family, 1 62, 1 72, 1 7 3 chemical

advances

hearth, i n furnace, 200 heat, 1 09- 1 1 8 ; measuring, 1 1 0; transfer of, 1 1 0- 1 1 1 , from nuclear explosions, 1 27

ment of light intensity, 1 03 force, total, 43; on a vertical sur­ face, 43; unbalanced, 6 3 ; lines of, around magnet, 8 1 forces, 1 9 , 29-40, 42; and mo­

hematite, 199 Henry, Joseph, 8 2 Hiroshima, bomb dropped on, 1 28 hormones, 2 1 7 horsepower (HP), 30; formula Huygens, Christian, 9 7 Hyatt, John, 2 1 8

fossils, carbon- 14, used to date

hydraulic lifts, 42

leum, 2 1 7 fractionating tower, 2 1 7 , 2 1 8 84;

of

a

sound wave, 92; of electro­ magnetic waves, 1 1 1; of X-rays, 1 1 9 friction, useful and harmful, 20; force of, 20, 29 fulcrum, 32, 3 3 , 34

hydraulics, and Pascal's Law, 44 hydrocarbons, 2 1 0; separation and collection of, in fractional distillation, 2 1 7 hydrometer, battery, 54 hyperon, 1 5 4 hypothesis ("educated guess"),

I

insulators, 7 1 internal combustion engines, 1 09

of, 1 62- 1 63 , 1 9 1 iron and steel, 1 99-206 isobutane, 209 isobutane, 2 1 0 isomers, 209 isotopes, 1 72 K Kelvin scale, 1 1 0 kiloliter, unit of volume, 1 4

kinetic energy, 29, 75; total aver� age, 1 09

krypton, result of splitting U-23 5 , 1 20

hearth, 20 1 ; basic oxygen, 2 0 1 -202; electric, 202 fusion reaction, 1 2 1 - 1 22 , 1 27

incandescent light, 103

lampblack, 209 lanthanide series, 1 7 1 , 1 74- 1 75 Lavoisier, Antoine, 1 46 Law of Conservation of Matter and Energy, 1 46, 1 64 Law of Electrical Charges, 69 Law of Flotation, 5 1 Law of Gravitational Attraction, 19 Law of Illumination, 1 03 Law of Inertia, 63 Law of Machines, 3 1 Law of Magnetic Poles, 8 1

illuminated objects, 1 0 1 illumination, intensity of,

1 0 3;

Law of, 1 03 incident ray of light, 1 0 1 inclined plane, 3 5 index o f refraction, 1 02 indicators, chemical, 1 9 1 induced current, 8 3 induced voltage, 84

Galileo, 62 galvanometer, 4, 7 1 , 8 3

induction method of making a

gamma rays, 99, 1 1 9 , 1 2 8 , 1 7 6 Geiger counter, 4

industry, chemical advances in,

242

instruments, string and wind, 9 3

L

hydrates, 1 8 1

fundamental tone, 93 furnaces: blast, 1 99-200; open­

G

ingot molds, 2 0 1 instruments, electrical, 7 0

for calculating, 3 1

tion, 6 1 -68 formula, chemical, 1 3 9, 1 541 5 5 , 1 64; structural, 209 age of, 1 7 3 , 176 fractional distillation, of petro-

Inertia, 1 9 , 2 1 , 29; Law of, 6 3 infra-red waves, 9 9

kilometer, measure of length, 1 2 kilotons, 1 27 kilowatts, 7 5

heavy water, 1 7 2- 1 7 3

unit of measure­

free neutrons, 1 2 1 frequency, electric,

in,

217

heat energy, 1 09, 1 1 2, 1 2 1

flux, 200 focal length, 1 04 foot-candles,

Hahn, Otto, 1 1 9

health,

1 72

1 29 ionization, 1 63 , 1 9 1 ions, and compounds, formation

half-life, of radioactive elements,

Fermi, Enrico, 1 1 9

1 62,

iodine-131, radioactive isotope, H

Faraday, Michael, 8 3

elements, 1 56,

magnet, 82

Law of Moments, 3 3 Law of Reflection, 1 0 1 length, metric units of, 1 2 lenses, convex, concave, 1 0 2 lever, the, 3 1 - 3 3 ; first-class, 3 2 ; second-class,

33,

third-class,

33 lift, force of, 5 5 light, 9 7- 1 08 ; nature of, 9 7 ; ve­ locity of, 97; theories of, 9798; dispersion of white, 99; reflection of, 1 0 1 ; refraction of, 99, 1 00; strength of a

source

of,

103;

measuring,

1 03 ; microscope, 1 04; polar­ ized, 1 04; speed of, 97, 1 1 1

factors, 1 6 ; common metric units, 12, 1 4, 1 5 , 1 6

Oersted, Hans, 82 Office of Civil Defense, 1 29

micrometer, 4

ohm, 7 1

light meter, exposure, 1 03

microscopes, light, 1 04; electron,

light microscope, 1 04 light year, 97

1 04 milliliter, unit of volume, 1 4

lightning, how caused, 70; rods, 70

mixtures, 1 37; major differences

Ohm's Law, 72, 74 opaque objects, 1 0 1 open-hearth furnace, 20 1 optical instruments, 1 04 optics, 1 1

lignite, formation of, 208

between compound and, 1 3 9 moderator, i n atomic pile, 1 2 1 ,

limestone, 200

1 28

limonite, 1 9 9

molecular forces, 22, 29

lines o f force, 8 1

molecular

liquid pressure, 43-44 liter, 1 3 litmus paper, 1 9 1

formula

of

some

lodestone, natural magnet, 8 1

ries, 2 1 1 molecular theory of matter, 1 451 47 molecular weight, 1 54; how to

lumens, 1 03 luminous objects, 1 0 1

determine, 1 55 molecules, 1 45, 146; polar, dipolar, 1 45

M

moment, of a force, 3 3

Mach, Ernst, 9 2 machines, 3 1 -36; Law of, 3 1 ; simple and compound, 3 1 -36 magnetic fields, 8 1 8 1 -90;

theory

of,

Moments, Law of, 3 3 momentum, 6 3 ; conservation of, 64 monomers, 2 1 8 Moseley, Henry, 1 7 1

81 magnetite, 1 9 9

motion, and forces, 6 1 -68; uniform and accelerated, 6 1

magnets, types of, 8 1 ; natural,

motors, electric, 84, 85 musical sounds, 9 3

8 1 ; artificial, 8 1

mutations, resulting from radio­

magnitude, of resultant, 22

activity, 1 27

manometers, 4 1 mass, 1 1 , 1 9 , defined, 1 3 7 matter, 1 1 ; chemistry of, 1 3 71 44; kinds of, 1 3 7 ; states and properties of, 1 45 ; and en­ ergy, 1 45- 1 5 2 Maxwell, James, 9 7 measurement, temperature, 3 ; in­ struments for, 4-5; units of, 1 2 mechanical advantage, of ma­ chines, 34; of hydraulic lift, 45 mechanical energy, 1 09 megatron, atom smasher, 1 2 1 meniscus, 1 4, 22

meson, 1 54 Metals, Activity Series of, 1 6 1 1 6 1 - 1 62,

non-metals, 1 72,

1 74,

n-butane, 2 1 0 native metals, 1 9 9 Nautilus, submarine, 1 20 nearsightedness, correction with lenses, 1 0 2 negative charges, electrical, 6 9 neoprene rubber, 2 1 9 neutralization reactions, 1 93 neutron, 69; d iscovery of, 1 1 9 , 153 Newton, Sir Isaac, 1 9, 62-64, 9 7 Nitrogen Family, 1 72, 1 7 3

mercury barometer, 4 1 Mesabi Range, 1 9 9

and

N

neutrino, 1 54

Mendeleyev, Dmitri, 1 7 1

metals,

organic and inorganic compounds, comparison of, 2 1 0 organic chemistry, 207- 2 1 6 outer ear, 94 overtones, 9 3

members of the methane se­

longitudinal waves, 9 1

magnetism,

millimeter, unit o f length, 1 2

1 3 9,

1 75

methane, 2 1 0; series, 2 1 0, 2 1 1 metric system, 3 , 1 2- 1 6; impor­ tant prefixes, 1 2; measuring in, 1 2 , measuring length in, 1 2,

non-conductor, 7 1 ; properties of, 1 3 9 , 1 62 nuclear energy, 1 09 , 1 1 9 ; present and future uses of, 1 22 nuclear fission, 1 1 9 ; fusion, 1 2 1 nuclear physics, 1 1 nuclear reactor, 1 20- 1 2 1 neutron, 69, 1 5 3

o

measuring area in, 1 2; meas­ uring volume in, 1 3 ; measur­ ing weight in, 1 5 ; conversion

observations, in an experiment, 2

P paraffin series, 2 1 0 parallel circuit, 7 3 particle, alpha, beta, 1 1 9 , 1 76; accelerators, 1 2 1 ; sub-nuclear, 1 54 Pascal's Law, 44, 45 peat, formation of, 208 Periodic t;rble, reading, 1 55 , 1 7 1 ; arrangement of elements into periods in the, 1 7 1 - 1 72; ar­ rangement of elements into groups

(families), 1 72; iso­ topes and radioisotopes, 1 721 73 ; families of elements in, 1 75; actinide 1 74- 1 75

series,

171,

petroleum, distillation of, 2 1 721 8 pH scale, 1 9 1 phenolphthalein (indicator), 1 9 1 photocell, 1 03 photometry, 1 0 3 photon, o r quantum, 97 physical change, definition of, 1 45 physical property of matter, 1 45 physics, introduction to, 1 - 1 36; defined, 1 1 ; branches of, 1 2; and the metric system, 1 1 - 1 8 pickling, process of, 1 9 2 pig iron, 200 pitch, of sound, 92 pitchblende, 1 1 9 Planck, Max, 97 plasma, 1 8 1 plastics, thermosetting, thermo­ plastic, 2 1 8 polarized light, 1 04 poles, of magnet, 8 1 ;

Law of

Magnetic, 8 1 ; N and S, 8 1 pollution of water, 1 8 6 polonium, i n pitchblende, 1 1 9 polymerization, process of, 2 1 8 polymers, 1 86, 2 1 8 polywater, 1 8 6 positive charges, 69

243

positron, 1 54

reflecting telescope, 1 04

potable water, 1 8 5 potential difference, 7 1 potential energy, 29

reflection, of light, 1 0 1 ; of heat energy, 1 1 1

power, defined, 30; mathematical formulas, 30; and energy, 75 prefixes, important metric, 3, 1 2 pressure, 4 1 -46; normal air, 42; defined, 42; liquid, 4 3 ; effect of shape, size and volume on, 4 3 ; exerted in all directions by liquids, 44 principal focus, 1 02 tion, 1 28 - 1 29 protoplasm, 1 8 1 , 207 protractor, 4

3 4 ; i n electricity, 7 3 , 7 4 resolution o f a force, 24 reverberation, of sound, 93 ring compounds, 2 1 0

roentgen, 1 29 Roentgen, Wi lhelm, 1 1 9

pure science, 1 1 purification, of water, 1 85

rotors, in generator, 84 rubber, natural, 2 1 8 ;

Q

synthetic

219 Rutherford, Sir Ernest, 1 1 9, 1 53

quality of a sound, 9 3 bundles

of

light energy, 97 quantum theory of light, 97 R radiant energy, 97, 1 09 radiation, transfer of heat energy by. 1 1 1 ; atomic, 1 1 9, 1 27 radicals, 1 5 6 radioactivity, 1 1 9 , 1 27

encing, 1 2 8 ; protective meas­ ures against, 1 28 - 1 29 radioactive isotopes, 1 29 ; haIf1 20,

1 72,

173;

beneficial uses of, 1 7 6 rarefaction, part of sound waves, 101,

S safety, in the laboratory, vii salts, definition, 1 9 1 ; 1 9 3 - 1 94; neutralization, 193; chemical reaction between a base and a, 1 94 satellite in orbit, 2 1 saturated ring of atom, 1 6 1 saturated solution, 1 8 3 Savannah, first nuclear-powered

radio telescope, 1 04 radio waves, 99 radioactive fallout, factors influ­

X-,

1 1 9;

reaction, chain, 1 1 9 reactions, chemical, combination or synthesis, 1 64; analysis or decomposition, 1 64; single and double replacement, 1 65 reactor, nuclear, 1 20 Redi, Francesco, 3 reducing agent, 200 reduction, process of, 1 99 refining, process of, 1 9 9 reflected ray o f light, 1 0 1

244

29; in machines, 3 1 , 3 2, 3 3 ,

RNA (ribonucleic acid), 2 1 7

pulses, sound vibrations, 9 1

9 1 , 92 rays, o f light, gamma, 1 1 9

resistance, four major types of,

rockets, 29

pulley, a simple machine, 3 6

life of, 1 29 radioisotopes,

dex of, 1 02 residue, from petroleum, 2 1 7

rings, shells, orbits, energy levels, 1 5 3 , 1 5 6, 1 6 1

protons, 69, 1 3 8 , 1 5 3

(photon)

refraction, of light, 99, 1 00; in­

resultant, the, 23

protection factor against radia-

quantum

refracting telescope, 1 04

merchant ship, 1 20 scalar quantities, 22, 6 1 scientific equipment, 3 , 4-5 scientific method, 1 -2 screw, a simple machine, 3 6 Seaborg, Glenn T., 1 3 8 sedimentation, 1 8 5 seeding, 1 84 SELF-DISCOVERY A CTIVITIES: Redi's Experiment, 6; Measuring length in the Metric System, 1 3 ; Measuring Vol­ ume in the Metric System, 1 4 ; Weighing in the Metric Sys­ tem, 1 5 ; To Determine the Center of Gravity of an Ir­ regular Object, 1 9-20; Explor­ ing the Force of Friction, 20-

2L Investigating Resultant and Equilibrant Forces, 24; Investigating the Law of Mo­ ments, 34-3 5 ; Work and the Inclined Plane, 3 6 ; Explor­ ing the Relationship B etween Water Pressure and Depth, 44; Investigating Hydraulic Pres-

sure, 46; Exploring Archi­ medes' Principle, 5 2 ; Deter­ mining the Specific Gravity of a Solid Denser Than Water, 54; Investigating Bernoulli's Principle, 56; Investigating an Example of Newton's Laws of Motion, 64 ; Investigating the Law of Electric Charges, 70; Investigating Parallel and Series Circuits, 75-76; Making an Electromagnet, 82; Using a Magnet to Induce an Electric Current, 85-86; What Causes Sound?, 9 1 ; Producing a Lon­ gitudinal Wave and Studying its Characteristics, 94; Pro­ ducing a Spectrum, 1 00-1 0 1 ; Investigating the Law of Il­ lumination, 1 03- 1 04; Investi­ gating Absorption and Radi­ ation of Heat, 1 1 1 - 1 1 2 ; Using a Thermocouple to Produce Electricity, 1 1 3- 1 1 4; Observ­ ing Nuclear Fission, 1 2 2 ; Con­ structing an Inexpensive De­ vice to Detect and Measure Atomic Radiation, 1 3 0 ; In­ vestigating Some Differences Between Mixtures and Com­ pounds, 1 40; Exploring Physi­ cal and Chemical Changes, 1 4 7 ; Making a Model of Atomic Structure, 1 5 6 ; In­ vestigating Electrolytes and Non-electrolytes, 1 65 ; Find­ ing Out About Newly Dis­ covered Elements, 1 76 ; In­ vestigating the Effect of Temperature on the Solubility of Carbon Dioxide, 1 82 ; Ex­ ploring the Effect of Particle Size, Stirring and Heating on the Rate at Which a Given Solute WiIl Dissolve, 1 8 3 ; In­ vestigating the Difference Be­ tween a Solution and a Suspen­ sion, 1 84; Discovering Some Materials Which Can Be Used to Soften Hard Water, 1 86 ; Investigating Some Properties of Acids and Bases, 1 94; Pro­ ducing Iron from Hematite, 202; Exploring Destructive Distillation, 208; Examining Organic Materials for Carbon, 2 1 1 ; Preparing a Polymer, 220 semiconductors, of electricity, 7 1 series circuit, 7 2 side-chain isomers, 2 1 8 silicones, 2 1 9 simple machines, types of, 3 6

single replacement, 1 92

suspensions, 1 84

skip cars, 1 99 slag, 200

symbols, chemical, 1 3 8 , 1 64 synchrotron, atom smasher, 1 2 1

valence, 1 5 6, 1 6 1 , 1 62 valence bond, 209 valence electrons, 1 56

slip rings, in generator, 8 3

synthetic elements, 1 3 8 synthetic fibers, 2 1 9 synthetic rubber, 2 1 9

variable, its use in an experi-

slugs, 1 20 soaking pits, 201 solute, 1 8 2 solutions, electrolytic, 7 1 , 1 84; types of: dilute, concentrated,

ment, 2 1 821 83 ;

1 8 3 ; saturated,

supersaturated, 1 8 3 solvent, 1 8 2 sonar, 9 3

9 1 ; waves, 9 1 ; characteristics of a wave, 92-93; velocity of, 92; pitch of, 92; reflection of, 9 3 ; musical , 9 3 ; how we hear, 9 3 -94 space exploration, 42 space ships, 1 9 specific gravity, and buoyancy, 5 1 -60; of solids denser than water, 5 3 ; of solids less dense than water, 5 3 ; of liquids, 5455; uses of, 55 specific heat of water, 1 8 1 spectroscope, use of, 1 04 spectrum, electromagnetic, 98-99 speed and velocity, 6 1 spherical photometer, 1 0 3 split rings, i n D C generator, 84 spontaneous disintegration, 1 1 9 spring scale, 1 9 standard candle, 1 0 3 stars, composition of, 1 3 8 static electricity, 69-70; dangers of, 70; useful applications of, 70 stators, in generator, 84 1 99-202,

206;

straight-chain hydrocarbons, 209, 218 Strassmann, Fritz, 1 1 9 in, 9 3 iso-

tope, 1 29 structural formulas, 209 submarines, 5 2 sub-nuclear particles, 1 54 subscript in a formula, 1 64 of

electricity,

72 supersaturated solution, 1 8 3

surface tension, 22

3,

velocity, and speed, 6 1 ; a vector quantity, 6 1 ; and sound, 92; supersonic, 92 Venturi tube, 5 6 Vernier caliper, 4 vibrations, of sound waves, 9 19 3 ; ultrasonic, 92 viruses, as seen with electron

theories and laws, 2-3 thermocouple, 1 1 3 thermodynamics, 1 1 2

volt, the, 7 1

microscope, 1 04 voltage drop, 7 3 , 74, 75

thermometer, 4, 1 1 2 thermonuclear reactions, 1 22 thermoplastic plastics, 2 1 8

voltmeter, 7 1 volume,

metric

units

of,

13

vulcanization, of rubber, 2 1 9

thermosetting plastics, 2 1 8 W

thermostats, 1 1 2 thiokol, 2 1 9 Thomson, Sir Joseph, 1 53

warning against atomic attack,

thrust, 5 6 total force, 43; how t o calculate, 43; on a vertical surface, 43 total kinetic energy, 1 09 transformer, 8 3 transistors, 7 1 transition elements, 1 72, 1 75 translucent object, 1 0 1

1 74-

transmutation, o f elements, 1 1 9 , 1 76 transparent object, 1 0 1 elements,

1 38,

1 3 9, 1 55 transverse waves, 97 turbine, 1 20 tuyeres, 1 9 9

1 13;

desalting

sea water, 1 22; properties of, 1 8 1 - 1 8 2; heavy, 1 8 1 ; purifica­ tion of, 1 85 ; hard and soft, 1 85; pollution, 1 8 6; conserva­ tion, 2 1 9 watt, unit o f electrical power, 75 wave length, 92; of light, 1 1 9 waves, sound, 9 1 -92; longitudinal, 9 1 ; transverse, 97; electro­ magnetic, 97 wedge, the, 35-36 weight, metric units of, 1 5, 1 9 ; defined, 1 3 7 wheel and axle, 3 6 wind, relative, 5 5

uniform acceleration, 6 2 uniform motion, 6 1 units, t o measure electricity, 7 1 72 Universal Gravitation, Law of, 19 universal solvent, water as, 1 8 1

v vaccines, chemical development of, 2 1 7

signals, 1 3 0 water, density,

white light, dispersion of, 9 9

ultrasonic vibrations, 9 2 unbalanced force, 6 3

supersonic velocity of sound, 92 superstitions, 3

measurement,

vector quantity, 6 1 vectors, 22

1 09 , 1 1 0 tension, surface, 22 textiles, synthetic, 2 1 9

U

stringed instruments, vibrations radioactive

temperature,

transuranium

alloys, 202

superconductors

taconite, 1 99 techniques and tools of science, telescope, refracting and reflect­ ing, 1 04; radio, 1 04

sound, 9 1 -96; how transmitted,

strontium-90,

T

1-10

sonic barrier, 92

steel, and iron,

Van de Graaf generator, 70 vaporization, 1 1 3

wind instruments, 9 3 wing, shape of, affect o n lifting force, 5 5 ; angle of tilt of, 5 5 Wohler, Friedrich, 207 work, defined, 29; mathematical formulas, 30 X X-rays, 98, 1 1 9, 1 20

z zero, absolute, 1 1 0 zones of destruction of atomic bomb, 1 27

245

ALPHABETICAL LISTING OF THE ELEM ENTS

Name

Symbol

Actinium . . . . . . Aluminum . . . . . Americium . . . . . Antimony Argon . . . Arsenic . Astatine . Barium . .

. . . . .

. . . . .

. . . . .

. . . . . . . . . . . . . . .

Berkelium Beryllium Bismuth . Boron . . . Bromine . Cadmium

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . .

. Calcium . . . . . . . Californium . . . .

Carbon . . . Cerium . . . Cesium . . . Chlorine . . Chromium Cobalt . . . . Copper . . . Curium . . . Dysprosium Einsteinium Erbium . . . Europium . Fermium . Fluorine . . Francium .

. . . . .

. . . . . . . . . . . . .

. . . . . . . .

. Gadolinium Gallium . . . Germanium Gold . . . . . . Hafnium . . .

. . . .

. . . .

. . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . .

. . . .

. . . .

. . . .

Helium . . Holmium Hydrogen Indium . .

. . . . . . . . . . . . . . . . . . . . . . . . Iodine . . . . . . . . . Iridium . . . . . . . . Iron . . . . . . . . . . Krypton . . . . . . .

Lanthanum . . . . Lawrencium . . . Lead . . . . . . . . . Lithium . . . . . . Lutetium . . . . . Magnesium . . .

. . . . .

Ac Al Am Sb Ar As At Ba

Bk Be Bi B Br Cd Ca Cf C Ce Cs Cl Cr Co Cu Cm Dy Es Er Eu Fm F Fr Gd Ga Ge Au Hf He Ho H In I Ir Fe Kr La Lw Pb Li Lu

.

Mg

Manganese . . . . . Mendelevium . . .

Mn Md

Atomic number

Atomic weight

89 13

( 227) 26.98 ( 243 ) * 1 2 1 . 76 3 9 . 944 74. 9 1 (210) * 1 37.36

95 51 18 33 85 56 97 4 83 5 35 48 20 98 6 58 55 17 24 27 29

247 * 9 .0 1 3 209.00 10.82 79.9 1 6 1 I 2 .4 l 40.08 ( 249 ) * 1 2 .0 1 1 1 40 . 1 3 132.91 35 .457 52.01 5 8 . 94 63.54

96 66 99 68 63

247 * 1 62 . 5 1

1 00

(253)

9 87 64 31 32 79 72 2 67 1 49 53 77 26 36 57 1 03 82 3 71 12 25 101

254* 1 67 . 27 1 5 2.0 1 9 .00

(223 ) * 1 57.26 69.72 7 2 . 60 1 97 . 0

1 78 . 5 0 4.003 1 64 . 9 4 1 .008 1 1 4.82 1 26.91 1 92 . 2 · 5 5.85 83.8 1 3 8 .92 ( 257 ) * 207.2 1 6.940 1 74. 99 24.32 54.94 ( 256 ) *

Name

Symbol

Atomic number

Atomic weight

Mercury . . . . . . . Molybdenum . . . Neodymium . . . . Neon . . . . . . . . . Neptunium . . . . .

Hg Mo

80 42

200.6 1 95.95

Nickel . . . Niobium . Nitrogen . Nobelium Osmium .

. . . . . . . . . . . .

. . . Oxygen . . . Palladium . Phosphorus

. . . . .

. . . . .

. . . . .

. . . . . . . . . .

. . . . .

Platinum . . . . . . . Plutonium . . . . . . Polonium . . . . . . Potassium . . . . . . Praseodymium . . Promethium

'

"

.

Protactinium . . . . Radium . . . . . . . . Radon . . . . . . . . . Rhenium . . . . . . . Rhodium . . . . . . . Rubidium . . . . . . Ruthenium . . . . . Samarium . . . . . . Scandium . . . . . .

Nd Ne Np Ni Nb N No Os 0 Pd P Pt

60 10 93 28 41 7 1 02 76 8 46 15 78

1 44.27 20. 1 8 3 (237 ) * 58.71 92.91 1 4 . 008 (253) 1 90.2 1 6.0000 1 06.4 30.975 1 95.09

Pu Po K Pr Pm Pa

61

( 1 4 5 ) ,',

91

( 23 1 )

Ra

88

Rn

86

Re Rh Rb Ru Sm Sc

94

( 242 ) *

84

(210)

19 59

3 9 . 1 00 1 40.92

226.05 ( 22 2 )

75

1 8 6.22

45 37

1 02 . 9 1

44

1 0 1 .7

62

1 50.35

21

44.96

8 5.48

34

78.96

·Silicon . . . . . . . . .

Se Si

14

2 8 .09

. . . . . . . . .

Ag

47

107.880

Na

11

22.99 1

Selenium . . . . . . . Silver

Sodium . . . . . . . Strontium . . . . . Sulfur . . . . . . . . Tantalum . . . . .

. . .

. Technetium . . . . . Tellurium . . . . . . Terbium . . . . . . . Thallium . . . . . . . Thorium . . . . . . . Thulium . . . . . . . Tin

. . . . . . . . . . .

Titanium . . . . . . . Tungsten . . . . . . . Uranium . . . . . . . Vanadium . . . . . . Xenon . . . . . . . . . Ytterbium . . . . . . Yttrium . . . . . . . . Zinc

. . . . . . . . . .

Zirconium . . . . . .

Sr S Ta Tc Te Tb Ti Th Tm Sn Ti W

38

8 7 . 63

16

3 2 .066

73

1 80.95

43

99*

52

1 27 . 6 1

65 81

204 . 3 9

90

2 3 2.05

69

1 68 .94

50

1 1 8 .70

1 58 . 9 3

22

4 7 . 90

74

1 8 3 . 86

U V

92

2 3 8 .07

23

50.95

Xe Yb

54

1 3 1 . 30

70

1 7 3 .04

39

88.92

Y Zn Zr

Numbers in parentheses are mass numbers of most stable or most common isotope.

30

65.38

40

9 1 .22