6 forces and motion compression guide: chapter planning guide · section 2 newton’s laws of...

Compression guide:To shorten instructionbecause of time limitations,omit Section 3.

OBJECTIVES LABS, DEMONSTRATIONS, AND ACTIVITIES TECHNOLOGY RESOURCES

6 Forces and MotionChapter Planning Guide

Chapter Opener

147A Chapter 6 • Forces and Motion

OSP Lesson Plans (also in print) TR Bellringer Transparency* SE Internet Activity, p. 156g

TR P20 Falling Objects Accelerate at aConstant Rate*

TR P21 Effect of Air Resistance on a FallingObject*

TR LINK TOLINK TO EARTH SCIENCEEARTH SCIENCE E58 Layers of theAtmosphere*

TR P22 How an Orbit Is Formed; ProjectileMotion*

CD Interactive Explorations CD-ROMExtreme Skiingg

CD Science Tutor

TE Demonstration Falling Objects, p. 150g TE Connection Activity Social Studies, p. 151a TE Connection Activity Math, p. 151g TE Connection Activity Earth Science, p. 152g TE Activity The Meaning of a Vacuum, p. 153b TE Connection Activity Astronomy, p. 154a TE Connection Activity Math, p. 155a SE Quick Lab Penny Projectile Motion, p. 156g SE Skills Practice Lab A Marshmallow Catapult,

p. 714gLB Inquiry Lab On the Fast TrackaLB Calculator-Based Labs Falling ObjectsaLB Calculator-Based Labs Graphing Your Motiona

Section 1 Gravity and Motion• Explain the effect of gravity and air resistance on

falling objects.• Explain why objects in orbit are in free fall and appear

to be weightless.• Describe how projectile motion is affected by gravity.

OSP Lesson Plans (also in print) TR Bellringer Transparency*CRF SciLinks Activity*g TR P23 Mass, Force, and AccelerationVID Lab Videos for Physical ScienceCD Science Tutor

TE Demonstration Egg in a Buggy, p. 158g SE Quick Lab First Law Skateboard, p. 159 ◆g

TE Connection Activity Real World, p. 159g SE Quick Lab First-Law Magic, p. 160g SE Connection to Environmental Science Car Sizes and

Pollution, p. 161g SE School-to-Home Activity Newton Ball, p. 163g TE Connection Activity Life Science, p. 163g SE Skills Practice Lab Inertia-Rama!, p. 170g SE Model-Making Lab Blast Off!, p. 715gLB Whiz-Bang Demonstrations Newton’s Eggciting

Experiment*bLB Whiz-Bang Demonstrations Inertia Can Hurt Ya*gLB Long-Term Projects & Research Ideas “Any Color You

Want, so Long as It’s Black”*a

PACING • 90 min pp. 158–165Section 2 Newton’s Laws of Motion• Describe Newton’s first law of motion, and explain

how it relates to objects at rest and objects in motion.• State Newton’s second law of motion, and explain the

relationship between force, mass, and acceleration.• State Newton’s third law of motion, and give

examples of force pairs.

OSP Lesson Plans (also in print) TR Bellringer Transparency*CD Science Tutor

TE Group Activity Testing Momentum, p. 166g SE Science in Action Math, Social Studies, and Language

Arts Activities, pp. 176–177g SE Skills Practice Lab Quite a Reaction, p. 716g

PACING • 45 min pp. 166–169Section 3 Momentum• Calculate the momentum of moving objects.• Explain the law of conservation of momentum.

OSP Parent Letter ■

CD Student Edition on CD-ROM CD Guided Reading Audio CD ■

TR Chapter Starter Transparency*VID Brain Food Video Quiz

SE Start-up Activity, p. 149gpp. 148–157PACING • 90 min

CRF Vocabulary Activity*g SE Chapter Review, pp. 172–173g

CRF Chapter Review* ■g

CRF Chapter Tests A* ■g, B*a, C*s SE Standardized Test Preparation, pp. 174–175g

CRF Standardized Test Preparation*gCRF Performance-Based Assessment*gOSP Test Generator, Test Item Listing

CHAPTER REVIEW, ASSESSMENT, ANDSTANDARDIZED TEST PREPARATION

PACING • 90 min

Online and Technology Resources

Visit go.hrw.com foraccess to Holt OnlineLearning, or enter thekeyword HP7 Homefor a variety of freeonline resources.

This CD-ROM package includes:• Lab Materials QuickList Software• Holt Calendar Planner• Customizable Lesson Plans• Printable Worksheets

• ExamView® Test Generator• Interactive Teacher’s Edition• Holt PuzzlePro®

• Holt PowerPoint® Resources

STANDARDS CORRELATION SKILLS DEVELOPMENT RESOURCES SECTION REVIEW AND ASSESSMENT CORRELATIONS

Chapter 6 • Chapter Planning Guide 147B

CRF Directed Reading A* ■b, B*s IT Interactive Textbook* Struggling ReadersStruggling Readers

CRF Vocabulary and Section Summary* ■g

SE Reading Strategy Reading Organizer, p. 150g SE Math Focus Calculating the Velocity of Falling Objects, p. 151g TE Reading Strategy Prediction Guide, p. 152g TE Inclusion Strategy, p. 153 TE Support for English Language Learners, p. 155 MS Math Skills for Science Arithmetic with Decimals*gCRF Reinforcement Worksheet Falling Fast*b

SE Reading Checks, pp. 151, 152, 154, 156g TE Reteaching, p. 156b TE Quiz, p. 156g TE Alternative Assessment, p. 156g SE Section Review,* p. 157 ■g

CRF Section Quiz* ■g

UCP 3; SAI 1, 2; ST 1; HNS 1, 2,3; PS 2c ; LabBook: SAI 1

CRF Directed Reading A* ■b, B*s IT Interactive Textbook* Struggling ReadersStruggling Readers


SE Reading Strategy Paired Summarizing, p. 158g TE Inclusion Strategy, p. 161 TE Support for English Language Learners, p. 161 SE Math Focus Second-Law Problems, p. 162g MS Math Skills for Science Newton: Force and Motion*g

SE Reading Checks, pp. 159, 161, 163, 164g TE Homework, p. 163b TE Reteaching, p. 164b TE Quiz, p. 164g TE Alternative Assessment, p. 164g SE Section Review,* p. 165 ■g


UCP 3, 4; SAI 1; PS 2b, 2c;Chapter Lab: SAI 1; PS 2bLabBook: SAI 1; PS 2c

SE Reading Checks, pp. 167, 168g TE Reteaching, p. 168b TE Quiz, p. 168g TE Alternative Assessment, p. 168a SE Section Review,* p. 169 ■g


SAI 1; LabBook: SAI 1CRF Directed Reading A* ■b, B*s IT Interactive Textbook* Struggling ReadersStruggling Readers


SE Reading Strategy Prediction Guide, p. 166g SE Math Focus Momentum Calculations, p. 167g TE Support for English Language Learners, p. 167 SE Connection to Language Arts p. 168g MS Math Skills for Science Momentum*gCRF Critical Thinking Forces to Reckon With*a

SE Pre-Reading Activity, p.148gOSP Science Puzzlers, Twisters & Teasersg

National ScienceEducation Standards

SAI 1; SPSP 5

CRF Chapter Resource File SS Science Skills Worksheets IT Interactive TextbookOSP One-Stop Planner MS Math Skills for Science Worksheets * Also on One-Stop Planner

SE Student Edition LB Lab Bank CD CD or CD-ROM ◆ Requires advance prepTE Teacher Edition TR Transparencies VID Classroom Video/DVD ■ Also available in Spanish

KEY

Maintained by the NationalScience Teachers Association.See Chapter Enrichment pagesthat follow for a complete listof topics.

www.scilinks.orgCheck out Current Sciencearticles and activities byvisiting the HRW Web siteat go.hrw.com. Just typein the keyword HP5CS06T.

• Lab Videos demonstratethe chapter lab.

• Brain Food Video Quizzeshelp students review thechapter material.

ClassroomVideos

Holt Lab GeneratorCD-ROM

Search for any lab by topic, standard,difficulty level, or time. Edit any labto fit your needs, or create your ownlabs. Use the Lab Materials QuickListsoftware to customize your labmaterials list.

• Guided Reading Audio CD(Also in Spanish)

• Interactive Explorations• Virtual Investigations• Visual Concepts• Science Tutor

ClassroomCD-ROMs

Planning ResourcesTEST ITEM LISTINGPARENT LETTERLESSON PLANS

Visual ResourcesCHAPTER STARTER

TRANSPARENCYBELLRINGER

TRANSPARENCIES

CONCEPT MAPPING TRANSPARENCYTEACHING TRANSPARENCIES

TEACHING TRANSPARENCIES

TEST ITEM LISTING

Copyright © by Holt Rinehart and Winston All rights reserved

The World of ScienceMULTIPLE CHOICE

1. A limitation of models is thata. they are large enough to see.b. they do not act exactly like the things that they model.c. they are smaller than the things that they model.d. they model unfamiliar things.Answer: B Difficulty: I Section: 3 Objective: 2

2. The length 10 m is equal toa. 100 cm. c. 10,000 mm.b. 1,000 cm. d. Both (b) and (c)Answer: B Difficulty: I Section: 3 Objective: 2

3. To be valid, a hypothesis must bea. testable. c. made into a law.b. supported by evidence. d. Both (a) and (b)Answer: B Difficulty: I Section: 3 Objective: 2 1

4. The statement "Sheila has a stain on her shirt" is an example of a(n)a. law. c. observation.b. hypothesis. d. prediction.Answer: B Difficulty: I Section: 3 Objective: 2

5. A hypothesis is often developed out ofa. observations. c. laws.b. experiments. d. Both (a) and (b)Answer: B Difficulty: I Section: 3 Objective: 2

6. How many milliliters are in 3.5 kL?a. 3,500 mL c. 3,500, 000 mLb. 0.0035 mL d. 35,000 mLAnswer: B Difficulty: I Section: 3 Objective: 2

7. A map of Seattle is an example of aa. law. c. model.b. theory. d. unit.Answer: B Difficulty: I Section: 3 Objective: 2

8. A lab has the safety icons shown below. These icons mean that you should weara. only safety goggles. c. safety goggles and a lab apron.b. only a lab apron. d. safety goggles, a lab apron, and gloves.Answer: B Difficulty: I Section: 3 Objective: 2

9. The law of conservation of mass says the tot al mass before a chemical change isa. more than the total mass after the change.b. less than the total mass after the change.c. the same as the total mass after the change.d. not the same as the total mass after the change.Answer: B Difficulty: I Section: 3 Objective: 2

10. In which of the following areas might you find a geochemist at work?a. studying the chemistry of rocks c. studying fishesb. studying forestry d. studying the atmosphereAnswer: B Difficulty: I Section: 3 Objective: 2

TEACHER RESOURCE PAGE

Lesson Plan

Section: Waves

PacingRegular Schedule: with lab(s): 2 days without lab(s): 2 days

Block Schedule: with lab(s): 1 1/2 days without lab(s): 1 day

Objectives1. Relate the seven properties of life to a living organism.

2. Describe seven themes that can help you to organize what you learn aboutbiology.

3. Identify the tiny structures that make up all living organisms.

4. Differentiate between reproduction and heredity and between metabolismand homeostasis.

National Science Education Standards CoveredLSInter6: Cells have particular structures that underlie their functions.

LSMat1: Most cell functions involve chemical reactions.

LSBeh1:Cells store and use information to guide their functions.

UCP1:Cell functions are regulated.

SI1: Cells can differentiate and form complete multicellular organisms.

PS1: Species evolve over time.

ESS1: The great diversity of organisms is the result of more than 3.5 billion yearsof evolution.

ESS2: Natural selection and its evolutionary consequences provide a scientificexplanation for the fossil record of ancient life forms as well as for the strikingmolecular similarities observed among the diverse species of living organisms.

ST1: The millions of different species of plants, animals, and microorganismsthat live on Earth today are related by descent from common ancestors.

ST2: The energy for life primarily comes from the sun.

SPSP1: The complexity and organization of organisms accommodates the needfor obtaining, transforming, transporting, releasing, and eliminating the matterand energy used to sustain the organism.

SPSP6: As matter and energy flows through different levels of organization ofliving systems—cells, organs, communities—and between living systems and thephysical environment, chemical elements are recombined in different ways.

HNS1: Organisms have behavioral responses to internal changes and to externalstimuli.

This CD-ROM includes all of the resources shown here and the following time-saving tools:

• Lab Materials QuickList Software

• Customizable lesson plans

• Holt Calendar Planner

• The powerful ExamView ® Test Generator

Chapter Resources

Dear Parent,

Your son's or daughter's science class will soon begin exploring the chapter entitled “The

World of Physical Science.” In this chapter, students will learn about how the scientific

method applies to the world of physical science and the role of physical science in the

world. By the end of the chapter, students should demonstrate a clear understanding of the

chapter’s main ideas and be able to discuss the following topics:

1. physical science as the study of energy and matter (Section 1)

2. the role of physical science in the world around them (Section 1)

3. careers that rely on physical science (Section 1)

4. the steps used in the scientific method (Section 2)

5. examples of technology (Section 2)

6. how the scientific method is used to answer questions and solve problems (Section 2)

7. how our knowledge of science changes over time (Section 2)

8. how models represent real objects or systems (Section 3)

9. examples of different ways models are used in science (Section 3)

10. the importance of the International System of Units (Section 4)

11. the appropriate units to use for particular measurements (Section 4)

12. how area and density are derived quantities (Section 4)

Questions to Ask Along the Way

You can help your son or daughter learn about these topics by asking interesting questions

such as the following:

• What are some surprising careers that use physical science?

• What is a characteristic of a good hypothesis?

• When is it a good idea to use a model?

• Why do Americans measure things in terms of inches and yards instead of centimeters

and meters ?

Layers of the AtmosphereThe Atmosphere TEACHING TRANSPARENCY

Copyright © by Holt, Rinehart and Winston. All rights reserved.

Temperature

Ozone layer

Temperature

Pressure

Thermosphere

Mesosphere

Stratosphere

Troposphere

Pressure

Alt

itud

e (k

m)

0

10

20

30

40

50

60

70

80

90

100

500

600

Lower Higher

Lower Higher

The layers of the atmosphere are defined by changes in temperature.

147C Chapter 6 • Forces and Motion

6

Chapter: The Atmosphere

You have been selected to travel on thespace shuttle as NASA’s first studentastronaut. Like all astronauts, you mustgo through a year of training to preparefor space travel. When you are in thespace shuttle, many different forces willbe acting on your body that might makeyou dizzy or disoriented. You must getused to these forces quickly before yougo into space.

There are many parts to your training.For instance, there is a machine that spinsyou around in all directions. There is alsounderwater training that lets you experi-ence what reduced gravity feels like. Butthe most exciting part of your training isriding on the KC-135 airplane.

The KC-135 is a modified airplane thatsimulates what it feels like to orbit Earthin the space shuttle. The KC-135 fliesupward at a steep angle, then flies down-ward at a 45° angle. When the airplaneflies downward, the effect of reduced grav-ity is produced inside. As the plane “falls”out from under the passengers, the astro-naut trainees inside the plane can “float,”as shown above. Because the floating oftenmakes passengers queasy, the KC-135 hasearned a nickname—the Vomit Comet.

NASA scientists used their knowledgeof forces, gravity, and the laws of motionto develop these training procedures. Inthis chapter, you will learn how gravityaffects the motion of objects and how thelaws of motion apply to your life.

Forces and Motion CHAPTER STARTER


Imagine . . .

Forces and Motion BELLRINGER TRANSPARENCY


Section: Gravity and MotionAnswer the following questions in your science

journal:

If Wile E. Coyote and a boulder fall off a cliff at the same time, which do you think will hit theground first? Would it matter if the cliff were veryhigh or particularly low? How could Mr. Coyote slowdown his fall?

Section: Newton’s Laws of MotionRespond to the following question in your science

journal:

If you are sitting still in your seat on a bus that istraveling 100 km/h on a highway, is your body at restor in motion? Explain your answer. Use a diagram ifit will help make your answer clear.

Falling Objects Accelerate at a Constant RateForces and Motion TEACHING TRANSPARENCY


1st s4.9 m

2nd s14.7 m

3rd s24.5 m

v � 0 m/s downward

v � 9.8 m/s downward




Forces an

d M

otio

nTEA

CHIN

G TR

AN

SPAR

ENCY

Effect of Air Resistance on a Falling Object

Then

et force

on the apple is the force of air resistance subtracted from

the force of gravity. B

ecause the net force is not 0 N

, the apple accelerates dow

nward. B

ut the apple does not accelerate as fast as it w

ould without

air resistance.

Thefo

rce of gravity

is pulling down on

the apple. If gravity w

ere the only force acting on the apple, the apple w

ould accelerate at a rate of 9.8 m

/s2.

Thefo

rce of air resistan

ceis push-

ing up on the apple. This force is subtracted from

the force of gravity to yield the net force.

a

bc

How an Orbit Is FormedForces and Motion TEACHING TRANSPARENCY


The space shuttle moves forward at a constant speed. If there were no gravity, the space shuttle would follow the path of the dotted line.

The path of the space shuttle follows the curve of Earth’s surface. Following this path is known as orbiting.

The space shuttle is in free fall because gravity pulls it toward Earth. The space shuttle would move straight down if it were not traveling forward.

c

b

a

Projectile Motion

a

c

b The ball’s vertical velocity increases because gravity causes it to accel-erate downward. The two motions

combine to form a curved path.

After the ball leaves the pitcher’s hand, the ball’s horizontal velocity is constant.


Forces an

d M

otio

nTEA

CHIN

G TR

AN

SPAR

ENCY

Mass, Force, and Acceleration

Acceleratio

nA

cceleration

Acceleratio

n

If the force applied to the carts is the same,

the acceleration of the empty cart is greater

than the acceleration of the loaded cart.

Acceleration w

ill increase when

a larger force is exerted.

when the upward force of

of

balances the downward

Falling objects

reach may be in

Forces and Motion CONCEPT MAPPING TRANSPARENCY


Use the following terms to complete the concept map below:force, free fall, terminal velocity, gravity, air resistance, projectile motion

SAMPLE SAMPLE SAMPLE

Meeting Individual Needs

Review and Assessments

Labs and Activities

DIRECTED READING A VOCABULARY ACTIVITY REINFORCEMENT

STANDARDIZED TESTPREPARATIONCHAPTER TEST BCHAPTER REVIEWSECTION QUIZ

SCILINKS ACTIVITY

MARINE ECOSYSTEMS

Go to www.scilinks.com. To find links relatedto marine ecosystems, type in the keywordHL5490. Then, use the links to answer thefollowing questions about marine ecosys-tems.

1. What percentage of the Earth’s surface iscovered by water?

2. What percentage of the Earth’s water is found in the oceans?

3. What is the largest animal on Earth?

4. Describe an ocean animal.

Name Class Date

SciLinks ActivityActivity

Developed and maintained by theNational Science Teachers Association

Topic: Reproductive SystemIrregularitiesSciLinks code: HL5490


Name Class Date

Vocabulary ActivityActivity

Getting the Dirt on the SoilAfter you finish reading Chapter: [Unique Title], try this puzzle! Use the clues belowto unscramble the vocabulary words. Write your answer in the space provided.

1. the breakdown of rock intosmaller and smaller pieces:AWERIGNETH

2. layer of rock lying beneath soil:CROKDEB

3. type of crop that is plantedbetween harvests to reduce soilerosion: CROVE

4. action of rocks and sedimentscraping against each other andwearing away exposed surfaces:SABRONIA

5. a mixture of small mineral frag-ments and organic matter: LISO

6. rock that is a source of soil:PRATEN CORK

7. type of reaction that occurs whenoxygen combines with iron toform rust: oxidation

8. type of weathering caused byphysical means: CLEMANIACH

9. the chemical breakdown of rocksand minerals into newsubstances: CAMILCHETHEARIGWEN

10. layers of soil, to a geologist:SNORHIZO

11. the uppermost layer of soil:SPOTOIL

12. process in which rainwater car-ries dissolved substances fromthe uppermost layers of soil to thebottom layers: HELANCIG

13. small particles of decayed plantand animal material in soil:MUUSH

14. the process in which wind, water,or ice moves soil from onelocation to another: ROOSINE

15. the methods humans use to takecare of soil:OSIL VASETONRICON

LONG-TERM PROJECTS &RESEARCH IDEAS

DATASHEETS FORQUICKLABS

DATASHEETS FORQUICK LABSCALCULATOR-BASED LABS

WHIZ-BANGDEMONSTRATIONS

VOCABULARY ANDSECTION SUMMARY


Section: EnergIn the space provided, write the letter of the description that best matches theterm or phrase.

______ 1. building molecules that can be used asan energy source. or breaking down moleculesin which energy is stored

______ 2. the process by which light energy is convertedto chemical energy

______ 3. an organism that uses sunlight or inorganicsubstances to make organic compounds

______ 4. an organism that uses sunlight or inorganicsubstances to make organic compounds

______ 5. an organism that consumes food to get energy

______ 6. the process of getting energy from food

In the space provided, write the letter of the term or phrase that best completeseach statement or best answers each question.

Name Class Date

Section QuizAssessment

a. photosynthesis

b. autotroph

c. heterotroph

d. cellular respiration

e. metabolism

f. cellular respiration

______ 7. Which of the following mostclosely resembles cellularrespiration?a. warm water moving

through copper pipesb. people movimg alomg a

escalatorc. mixing different foods in

a blenderd. logs burning in a fire

______ 8. An organism’s reproductivecells, such as sperm or eggcells, are called?a. genesb. chromosomesc. gamates.d. zygotes.

______ 9. An organism’s reproductivecells, such as sperm or eggcells, are called?a. genesb. chromosomesc. gamates.d. zygotes.

______10. Which of the following mostclosely resembles cellularrespiration?a. warm water moving

through copper pipesb. people movimg alomg a

escalatorc. mixing different foods in

a blenderd.

logs burning in a fire


Section: ExploringTHAT’S SCIENCE!

1. How did James Czarnowski get his idea for the penguin boat, Proteus?Explain.

2. What is unusual about the way that Proteus moves through the water?

MATTER + AIR ➔ PHYSICAL SCIENCE

3. What do air, a ball, and a cheetah have in common?

4. What is one question you will answer as you explore physical science?

5. Chemistry and physics are both fields of . Chemists

study the different forms of and how they interact.

and how it affects are

studied in physics.

Identify the field of physical science to which each of the following descriptionsbelongs by writing physics or chemistry in the space provided.

_______________________ 6. how a compass works

_______________________ 7. why water boils at 100°C

_______________________ 8. how chlorine and sodium combine to form table salt

_______________________ 9. why you move to the right when the car you are inturns left

Directed Reading A

Name Class Date

Skills Worksheet

DIRECTED READING B

Section: ExploringTHAT’S SCIENCE!

1. How did James Czarnowski get his idea for the penguin boat, Proteus?Explain.

2. What is unusual about the way that Proteus moves through the water?

MATTER + AIR ➔ PHYSICAL SCIENCE

3. What do air, a ball, and a cheetah have in common?

Directed Reading B

Name Class Date

Skills Worksheet

Section: UniqueVOCABULARY

In your own words, write a definition of the following term in the space provided.

1. scientific method

2. technology

3. observation

Name Class Date

Vocabulary & NotesSkills Worksheet

Name Class Date

ReinforcementSkills Worksheet

The Plane TruthComplete this worksheet after you finish reading the Section: [Unique SectionTitle]

You plan to enter a paper airplane contest sponsoredby Talkin’ Physical Science magazine. The personwhose airplane flies the farthest wins a lifetime sub-scription to the magazine! The week before the con-test, you watch an airplane landing at a nearbyairport. You notice that the wings of the airplane haveflaps, as shown in the illustration at right. The paperairplanes you’ve been testing do not have wing flaps.What question would you ask yourself based on these observations? Write yourquestion in the space below for “State the problem.” Then tell how you could usethe other steps in the scientific method to investigate the problem.

1. State the problem.

2. Form a hypothesis.

3. Test the hypothesis.

4. Analyze the results.

5. Draw conclusions.

Flaps


CRITICAL THINKING

A Solar Solution

Name Class Date

Critical ThinkingSkills Worksheet

Joseph D. Burns

Inventors’ Advisory Consultants

Portland, OR 97201

Dear Mr. Burns,I’ve got this great idea for a new product called the BlissHeater. It’s a portable, solar-powered space heater. The heater’s design includes these features:•T

he heater will be as longas an adult’s arm and aswide as a

packing box.

•T

he heater will have aglass top set at an angleto catch the sun’s rays.

•T

he inside of the heaterwill be dark colored toabsorb solar heat.If you think my idea will work, I will make the Bliss

Heaters right away without wasting time and money on test-ing and making models. Please write back soon with youropinion.

SECTION REVIEW

Section: UniqueKEY TERMS

1. What do paleontologist study?

2. How does a trace fossil differ from petrified wood?

3. Define fossil.

UNDERSTANDING KEY IDEAS

Name Class Date

Section ReviewSkills Worksheet


[UniqueMULTIPLE CHOICE


______ 1. Surface currents are formed bya. the moon’s gravity. c. wind.b. the sun’s gravity. d. increased water density.

______ 2. When waves come near the shore,a. they speed up. c. their wavelength increases.b. they maintain their speed. d. their wave height increases.

______ 3. Longshore currents transport sedimenta . out to the open ocean. c. only during low tide.b. along the shore. d. only during high tide.

______ 4. Which of the following does NOT control surface currents?a. global wind c. Coriolis effectb. tides d. continental deflections

______ 5. Whitecaps breaka. in the surf. c. in the open ocean.b. in the breaker zone. d. as their wavelength increases.

______ 6. Most ocean waves are formed bya . earthquakes. c. landsides.b. wind. d. impacts by cosmic bodies.

______ 7. Which factor controls surface currents?a. global winds c. continental deflectionb. the Coriolis effect d. all of the above

______ 8. Streamlike movments of ocean water far below the surface arecalleda. jet currents c. surface currents.b. Coriolis currents. d. deep currents.

______ 9. When the sunlit part of the moon that can be seen from Earthgrows larger, it isa. waxing. c. in the new moon phase.b. waning. d. in the full moon phase.

______10. The Milky Way is thought to bea. an elliptical galaxy. c. a spiral galaxy.

Name Class Date

Chapter Test BAssessment


READING

Read the passages below. Then, read each question that follows the passage.Decide which is the best answer to each question.

Passage 1 adventurous summer camp in the world. Billy can’twait to head for the outdoors. Billy checked the recommendedsupply list: light, summer clothes; sunscreen; rain gear; heavy,down-filled jacket; ski mask; and thick gloves. Wait a minute! Billythought he was traveling to only one destination, so why does heneed to bring such a wide variety of clothes? On further investiga-tion, Billy learns that the brochure advertises the opportunity to“climb the biomes of the world in just three days.” The destinationis Africa’s tallest mountain, Kilimanjaro.

______ 1. The word destination in this passage meansA camp B vacation.C place. D mountain.

______ 2. Which of the following is a FACT in the passage?F People ski on Kilimanjaro.G Kilimanjaro is Africa’s tallest mountain.H It rains a lot on Kilimanjaro.J The summers are cold on Kilimanjaro.

______ 3. Billy wondered if the camp was advertising only one destination afterhe read the brochure, which said thatA the camp was the most adventurous summer camp in the world.B he would need light, summer clothes and sunscreen.C he would need light, summer clothes and a heavy, down-filled

jacket.D the summers are cold on Kilimanjaro.

Name Class Date

Standardized Test PreparationAssessment

PERFORMANCE-BASEDASSESSMENT

OBJECTIVEDetermine which factors cause some sugar shapes to break down faster than others.

KNOW THE SCORE!As you work through the activity, keep in mind that you will be earning a gradefor the following:

• how you form and test the hypothesis (30%)

• the quality of your analysis (40%)

• the clarity of your conclusions (30%)

ASK A QUESTIONSWhy do some sugar shapes erode more rapidly than others?

MATERIALS AND EQUIPMENT

Name Class Date

Performanced-Based AssessmentAssessment SKILL BUILDER

Using Scientific Methods

• 1 regular sugar cube • 90 mL of waterCopyright © by Holt, Rinehart and Winston. All rights reserved.

USING VOCABULARY

1. Define biome in your own words.

2. Describe the characteristics of a savanna and a desert.

3. Identify the relationship between tundra and permafrost.

4. Compare the open-water zone and the deep-water zone.

5. Use each of the following terms in an original sentence: plankton, littoralzone, and estuary.

6. Describe how marshes and swamps differ.

Name Class Date

Chapter ReviewSkills Worksheet

SCIENCE PUZZLERS,TWISTERS & TEASERS

CHAPTER TEST A






______ 4. Which of the following does NOT control surface currents?a global wind c Coriolis effect

Name Class Date

Chapter Test AAssessment

CHAPTER TEST C






______ 4. Which of the following does NOT control surface currents?a global wind c Coriolis effect

Name Class Date

Chapter Test CAssessment

36 HOLT SCIENCE AND TECHNOLOGY

Cop

yrig

ht©

byH

olt

Rine

hart

and

Win

ston

All

right

sre

serv

ed

Name _______________________________________________ Date ________________ Class______________

Graphs made using a motion detector can be used to study motion. In thisexperiment, you and a partner will use a motion detector to make graphsof your own motion.

Procedure

Part A: Distance vs. Time Graphs1. Fasten a motion detector to a tabletop facing

an area free of furniture and other objects. The motiondetector should be at a height of about 15 cm above yourwaist level.

2. Use short strips of masking tape on the floor to mark 1 m, 2 m, 3 m, and 4 m distances from the motion detector.

3. Plug the motion detector into the DIG/SONIC 1 port of theLabPro or CBL 2 interface. Use the link cable to connect theTI graphing calculator to the interface. Firmly press in thecable ends.

4. Turn on the calculator and start the DatMatch program.Press to reset the program.

5. Set up the calculator and interface for data collection bycompleting the following steps.

a. Use and to select MODE.

b. Press to change the mode to TIME GRAPH.6. Explore making Distance vs. Time graphs by completing the

following steps.

a. Stand at the 1.0 m mark, facing away from the motiondetector.

b. Signal your partner to select START.

c. Slowly walk to the 2.5 m mark and stop.

d. When data collection ends, select DISTANCE from theSELECT GRAPH menu.

e. Plot your data on the graph on the next page.

f. Press to return to the SELECT GRAPH menu.

g. Select RETURN TO MAIN SCREEN to return to the mainscreen.

7. Repeat step 6 while walking faster. Sketch your new line onthe same graph.

STUDENT WORKSHEET9

Graphing Your Motion

MATERIALS

• LabPro or CBL 2 inter-face

• TI graphing calculator• DatMatch program• Vernier motion detec-

tor• masking tape• meter stick

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TEACHER-LED DEMONSTRATION

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Newton’s Eggciting ExperimentPurpose

Students are introduced to Newton’s firstlaw of motion.

Time Required

10–15 minutes

What to Do

1. Fill the glasses three-quarters full of wa-ter.

2. Arrange the glasses in a triangle near anedge of the table, as shown in the illus-tration at right. Set the pie pan on topof the glasses so that one edge of thepie pan extends over the edge of thetable. If necessary, reposition the

glasses. Place a cardboard tube verti-cally over each glass. Then place an eggsideways on top of each tube.

3. Stand the broom at the edge of thetable so that the handle touches theedge of the pie pan. Carefully step onthe bristles of the broom to hold it inplace.

4. Tell students that you will knock theedge of the pie pan with the broom.Challenge them to predict what willhappen. (Accept all reasonable responses.)

5. Pull the broom handle toward you, andthen release it.

6. The broom handle should spring for-ward, driving the pie pan and the tubesout from under the eggs. The eggsshould drop into the glasses of waterdirectly below them.

Discussion

Have students work together in smallgroups to come up with an explanation ofwhat happened. Suggest that they useNewton’s first law, which states that anobject at rest remains at rest and an objectin motion remains in motion at constantspeed and in a straight line unless actedupon by an unbalanced force.

Explanation

The broom applied force to the pie pan.When the edge of the pie pan struck thetubes, some of the force was transferred tothe tubes. The tubes did not transferenough of this force to the eggs to over-come their inertia. Therefore, the eggs re-mained in place until their support wasremoved. Gravitypulled the eggsdownward until thewater cushionedtheir fall and ab-sorbed their down-ward energy.

MATERIALS

• 3 drinking glasses or clear plastic cups• tap water• pie pan• 3 cardboard bathroom-tissue tubes• 3 eggs• broom

TEACHER PREP

CONCEPT LEVEL

CLEAN UP

E A S Y H A R D

Lab Ratings

Harriet KnopsRolling Hills Middle School

El Dorado, California

Chapter 6 • Chapter Resources 147D

For a preview of available worksheets covering math and science skills,see pages T26–T33. All of these resources are also on the One-Stop Planner®.

Letter Comet1. Commander Eileen Collins was playing Scrabble® with her four-

man crew on board the KC-135. In this game, new words areformed by adding wooden tiles, each with a letter and a pointvalue, to a board. Each word must share at least one letter withthe word it crosses. The numbers on the tiles are added to find thescore for each word. When the crew of the KC-135 play, they useonly words from their favorite chapter, “Forces in Motion.”

Just after Commander Collins spelled centripetal on the board,the KC-135 tipped downward, throwing many of the tiles into freefall. Only the tiles that were sticky from yesterday’s orange-juicespill didn’t fly off. Help them figure out where the other tilesbelong. (Each tile is used only once.) Write the correct letters onthe board.

Name _______________________________________________ Date ________________ Class______________

SCIENCE PUZZLERS, TWISTERS & TEASERS6

Forces in Motion

CHAPTER

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1 1 1 1 3 1 1 1 41

And Away We Go1. Cars are always changing! Research the changes made in the

design of automobiles over the last century. Do these changesmake cars safer, faster, or more fuel efficient? Think of

two new design changes that could improve thesafety or efficiency of a car. Create a poster displaywith pictures of the car and illustrations of yournew design elements. Also include explanations of

the changes’ benefits on your poster.

Another Research Idea2. A Major League Baseball pitcher can throw a ball at

150 km/h (93 mph). Can you imagine how much energyit would take to make a ball travel 20 times faster thanthat? Well, scientists are working on a device called a ramaccelerator that could accelerate objects to hypervelocity—speeds much faster than the speed of sound. In a ramaccelerator, a huge force acts on the small mass of the pro-jectile to achieve rapid acceleration. How does a ram accel-erator work? What generates the huge force that acts onthe projectile? What are the potential uses for a ram accel-erator? Write an article about the development of the ramaccelerator and its potential uses.

Long-Term Project Idea3. Interview a race car driver, bicycle racer, or stunt driver

about how speed, acceleration, and momentum affectthem in their line of work. Also ask them aboutthe effects of gravity and friction on vehiclemovement. Videotape or tape-record yourinterview. Present your recording, along withsimple demonstrations, to a younger class toteach them about the forces of motion.

Name ___________________________________________________ Date _________________ Class _____________

PROJECT

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“Any Color You Want, So Long as It’s Black”

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When the Model T Ford rolled off the production lines in 1914, it was offered inonly one color—black. Black paint dried much faster than other colors, so HenryFord’s car factories could make more automobiles in less time by painting theircars black. Ford was famously quoted as saying that you could get a Ford in “anycolor you want, so long as it’s black.” It wasn’t until 1926 that the Model T wasoffered in other colors. Think of all the colors that cars come in today! The roadstoday are filled with cars of every color from black to lime green. Cars have changeda lot since 1914 and in more exciting ways than just the color of their paint.

CALCULATOR-BASED LABS

Galileo demonstrated that falling objects accelerate downward at the same rateregardless of their mass. However, this is true only when there is little to no airresistance compared to the mass of the falling object. Air resistance can causeobjects to fall at different rates. For example, air resistance enables a skydiver’sparachute to slow his or her fall to the ground. When the force from air resis-tance of a falling object equals the weight of the object, acceleration stops andthe object is said to have reached its maximum, or terminal, velocity. In thisexperiment, you will study and compare the velocities of two different fallingobjects.

Procedure

1. Set up the apparatus as shown in the illustration by com-pleting the following steps.

a. Place the ring stand at the edge of your lab table.

b. Place two books on the base of the ring stand to keep itfrom falling.

c. Use a right-angle clamp to fasten a metal rod to the ringstand.

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Falling Objects

LAB

Name _______________________________________________ Date ________________ Class______________

MATERIALS

• LabPro or CBL 2interface

• TI graphing calculator• DataMate program• Vernier motion

detector• ring stand• metal rod• right-angle clamp• basket coffee filter Copyright © by Holt, Rinehart and Winston. All rights reserved.Copyright © by Holt, Rinehart and Winston. All rights reserved.


Name Class Date

Reaction to StressQuick Lab DATASHEET FOR QUICK LAB

BackgroundThe graph below illustrates changes that occur in the membrane potential of aneuron during an action potential. Use the graph to answer the followingquestions. Refer to Figure 3 as needed.

Analysis1. Determine about how long an action potential lasts.

2. State whether voltage-gated sodium, chanels are open or closed at point A.

3. State whether voltage-gated potassium channels are open or closed atpoint B.

4. Critical Thinking Recognizing Relationships What causes the menberneotential to become less negative at point A?

5. Critical Thinking Recognizing Relationships What causes the membranepotential to become more negative at point B?


Answer here.

Answer here.

Answer here.

Answer here.

Answer here.

Using Scientific Methods

INQUIRY LABS

STUDENT WORKSHEET

LAB

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Name Date Class

As the chief design engineer for a new theme park, you mustensure that all rides and attractions are the biggest, fastest,tallest, safest, and most thrilling in the world.

Your latest assignment is to design the world’s fastestwooden roller coaster. The roller coaster must have one loopand two hills. Your first task is to build a model for the rollercoaster. If the design is sound, the model will serve as theprototype for a new roller coaster called the Eliminator. Thepark owner and visitors expect the Eliminator to be the mainattraction at the theme park’s grand opening next year.

On the Fast Track

Ask a QuestionHow do you build a model roller coaster to meetthe following criteria?

• It includes a loop that is at least 50 cm in height.

• It includes two hills.

• It includes safety features to protect the rider (ball bearing).

MATERIALS

• support stand andclamps

• 4 m of clear vinyl tub-ing

• ball bearing• small paper cup



GENERAL

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SPECIAL NEEDS

SPECIAL NEEDS GENERAL

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DATASHEETS FORCHAPTER LABS

Teacher’s NotesTIME REQUIRED

One 45-minute class period.

RATINGTeacher Prep–3Student Set-Up–2Concept Level–2Clean Up–2

MATERIALS

The materials listed on the student page are enough for a group of 4–5 students.Large, dried beans of any kind will work well in this exercise.

SAFETY CAUTION

Remind students to review all safety cautions and icons before beginning this labactivity.

Using Scientific MethodsSkills Practice Lab DATASHEET FOR CHAPTER LAB


1 2 3 4Easy Hard

Jason MarshMontevideo High

and Country School

SAMPLE

DATASHEETS FORLABBOOK

Teacher’s NotesTIME REQUIRED

One 45-minute class period.

Does It All Add Up?Skills Practice Lab DATASHEET FOR LABBOOK LAB


Jason MarshMontevideo High

SAMPLE

This Chapter Enrichment provides relevant and

interesting information to expand and enhance

your presentation of the chapter material.

Gravity and MotionThe Apple and the Moon• Galileo’s theory that all objects fall with the same

acceleration has been verified on Earth many times. It wasn’t the same old proof, though, on July 30, 1971, when astronaut David Randolph Scott stood on the surface of the moon and dropped a feather and a hammer simultaneously. Just as Galileo’s theory had predicted, in the absence of air resistance, the feather hit the ground at the same time as the hammer.

• Sir Isaac Newton is said to have realized the importance of gravitational force in 1666, when he watched an apple fall from a tree in his garden. John Conduitt, one of Newton’s contemporaries, said of Newton, “. . . [I]t came into his thought that the power of gravity (which brought an apple from the tree to the ground) was not limited to a certain distance from the earth, but that this power must extend much further than was usually thought. Why not as high as the Moon though he said to himself & that if so, that must influence her motion & perhaps retain her in her orbit. [W]hereupon he fell a-calculating what would be the effect of that supposition. . .”

• Newton calculated the acceleration of the moon in a circular orbit around Earth and compared this with an apple’s downward acceleration. He discovered that the acceleration of the moon was approximately 3,600 times smaller than the acceleration of an object

near the surface of Earth. Newton eventually accounted for this difference by assuming that the gravitational force was inversely proportional to the square of the distance from Earth.

Air Resistance and Terminal Velocity• Air resistance, a type of friction, limits the velocity

of an object as it falls. As long as a falling object is somewhat streamlined and has not accelerated to high velocity, its acceleration due to gravity near the surface of Earth is a constant 9.8 m/s2.

• As the velocity of a falling object increases, more air must be pushed out of the way each second. Eventually, the force of the air resistance pushing upward on the falling object is equal to Earth’s gravitational force pulling downward on the object.

• When the upward and downward forces are equal, the net force on the falling object is 0 N. Then,the object falls with a constant velocity, called the terminal velocity.

Parachutes• How do para-

chutes work to increase air resistance? The parachute pro-vides a larger surface area to pull through the air. The larger sur-face area requires a much larger amount of air be moved out of the way each second as the parachute falls toward Earth.

Chapter Enrichment

147E Chapter 6 • Forces and Motion

6

Is That a Fact!◆ Galileo timed the motion of balls rolling down an

inclined plane to prove that all objects fall with thesame acceleration.

Newton’s Laws of MotionSir Isaac Newton (1642–1727)• In 1661, Isaac Newton went to study at Cambridge

University. But Newton made many of his mostimportant discoveries while spending time at thefamily home, Woolsthorpe Manor, near Grantham,in Lincolnshire, England, in 1665 and 1666.

Principia• Newton’s Principia, published in 1687, explains the

three basic laws that govern the way objects move andNewton’s theory of gravity. Newton explained how theforce of gravity keeps the planets moving around thesun. Interestingly, Newton used his laws to predict thatEarth must be a slightly flattened sphere and thatcomets orbit the sun in elongated elliptical paths.These predictions were later shown to be true.

Frogs and Fastballs• What does a jumping frog have in common with

a 42 m/s fastball? What does the space shuttle havein common with a sky diver? They are all affected bygravity, and their flights are governed by certain lawsof motion. Although some observers in ancient Chinatheorized about objects in motion and objects at rest,Newton is usually given credit for stating and testingthe three basic laws that describe and predict motion.

MomentumMomentum and Martial Arts• Momentum is the

product of an object’smass and its velocity.Like velocity, momen-tum always includes adirection. The directionof an object’s momen-tum is always in thedirection of its motion.

• When a person (the attacker) kicks or throws a punchduring a martial arts match, the attacker has momen-tum in the forward direction. The attacker’s opponentcan take advantage of this momentum when blockingthe hit. Instead of trying to stop the hit, the opponentsweeps the attacker’s arm or leg away with his or herown arm. This motion redirects the hit away from theopponent’s body. The attacker’s momentum continuesin a generally forward direction, which can cause theattacker to lose his or her balance.

For background information about teaching strategies and

issues, refer to the Professional Reference for Teachers.

Topic: Force of GravitySciLinks code: HSM0602

Topic: Gravity and OrbitingObjects

SciLinks code: HSM0692

Topic: Projectile MotionSciLinks code: HSM1223

Topic: Newton’s Laws (of Motion)SciLinks code: HSM1028

Topic: MomentumSciLinks code: HSM0988

Visit www.scilinks.org and enter the SciLinks code formore information about the topic listed.

SciLinks is maintained by the National Science Teachers Associationto provide you and your students with interesting, up-to-date links thatwill enrich your classroom presentation of the chapter.


Chapter 6 • Chapter Enrichment 147F

Standards Correlations

OverviewIn this chapter, students willlearn about gravity’s role inthe acceleration of fallingobjects, in orbiting, and in pro-jectile motion. Students will alsostudy Newton’s laws of motion.Finally, students will learn howto calculate momentum and willstudy the law of conservation ofmomentum.

Assessing PriorKnowledgeStudents should be familiarwith the following topics:

• velocity and acceleration

• net force and balanced andunbalanced forces

• friction

• gravity

IdentifyingMisconceptionsSome students may think thatan object will stay in motiononly if a force continuouslyacts on the object. Explain tostudents that a force is neededto start the motion of an objectbut that the object will continueto move if no other forces (suchas friction) act on the object.Discuss an air-hockey puck asan example of an object thatmoves with a (nearly) constantspeed after the force causing itsmotion has ended.

National Science Education Standards

The following codes indicate the National Science EducationStandards that correlate to this chapter. The full text of thestandards is at the front of the book.

Chapter OpenerSAI 1; SPSP 5

Section 1 Gravity and MotionUCP 3; SAI 1, 2; HNS 1, 2, 3; PS 2c; LabBook: SAI 1

Section 2 Newton’s Laws of MotionUCP 3, 4; SAI 1; ST 1; PS 2b, 2c; LabBook: SAI 1; PS 2c

Section 3 MomentumSAI 1; LabBook: SAI 1

Chapter LabSAI 1; PS 2b

Chapter ReviewPS 2b

Science in ActionST 1, 2; HNS 1; SPSP 5

148 Chapter 6 • Forces and Motion

6

Forcesand Motion

About the

To train for space fl ight, astronauts fl y in amodifi ed KC-135 cargo airplane. The airplanefi rst fl ies upward at a steep angle. Then, itfl ies downward at a 45° angle, which causesthe feeling of reduced gravity inside. Underthese conditions, the astronauts in the planecan fl oat and can practice carrying out tasksthat they will need to perform when they arein orbit. Because the fl oating makes peoplequeasy, this KC-135 is nicknamed the “VomitComet.”

Spider Map Beforeyou read the chapter,create the graphic orga-

nizer entitled “Spider Map” described inthe Study Skills section of the Appendix.Label the circle “Motion.” Create a legfor each law of motion, a leg for gravity,and a leg for momentum. As you readthe chapter, fillin the map withdetails about howmotion is relatedto the laws ofmotion, gravity,and momentum.

SECTION

Unbalanced forces causechanges in motion that canbe predicted and described.

6

1 Gravity and Motion . . . . . . . . . 150

2 Newton’s Laws of Motion . . . 158

3 Momentum . . . . . . . . . . . . . . . . 166

START-UPFalling WaterGravity is one of the most important forces in your life. In this activity, you will observe the effect of gravity on a falling object.

Procedure1. Place a wide plastic tub on the floor. Punch a

small hole in the side of a paper cup, near the bottom.

2. Hold your finger over the hole, and fill the cup with water. Keep your finger over the hole, and hold the cup waist-high above the tub.

3. Uncover the hole. Record your observations as Trial 1.

4. Predict what will happen to the water if you drop the cup at the same time you uncover the hole.

5. Cover the hole, and refill the cup with water.

6. Uncover the hole, and drop the cup at the same time. Record your observations as Trial 2.

7. Clean up any spilled water with paper towels.

Analysis1. What differences did you observe in the behavior

of the water during the two trials?

2. In Trial 2, how fast did the cup fall compared with how fast the water fell?

3. How did the results of Trial 2 compare with your prediction?

Chapter 6 • Forces and Motion 149

START-UPSTART-UP vvM A T E R I A L S

FOR EACH GROUP• cup, paper• paper towels• tub, wide plastic• water

Teacher’s Notes: Food coloring may be added to the water so that students will see the water better. Furthermore, the activity can be done outdoors to mini-mize cleanup.

To reduce the mess, have stu-dents fill the cups only half full. Spread plenty of newspapers on the floor.

Answers

1. In Trial 1, students should see the water coming out of the hole and falling to the ground. In Trial 2, they should not see any water coming out of the hole as the cup falls.

2. The cup and the water fall at the same rate. Students may not know that both are accelerating, and students may say that both fell with the same velocity, or speed.

3. Sample answer: My prediction was wrong because I thought the water would come out of the cup faster, but no water came out at all.

You have been selected to travel on thespace shuttle as NASA’s first studentastronaut. Like all astronauts, you mustgo through a year of training to preparefor space travel. When you are in thespace shuttle, many different forces willbe acting on your body that might makeyou dizzy or disoriented. You must getused to these forces quickly before yougo into space.

There are many parts to your training.For instance, there is a machine that spinsyou around in all directions. There is alsounderwater training that lets you experi-ence what reduced gravity feels like. Butthe most exciting part of your training isriding on the KC-135 airplane.

The KC-135 is a modified airplane thatsimulates what it feels like to orbit Earthin the space shuttle. The KC-135 fliesupward at a steep angle, then flies down-ward at a 45° angle. When the airplaneflies downward, the effect of reduced grav-ity is produced inside. As the plane “falls”out from under the passengers, the astro-naut trainees inside the plane can “float,”as shown above. Because the floating oftenmakes passengers queasy, the KC-135 hasearned a nickname—the Vomit Comet.

NASA scientists used their knowledgeof forces, gravity, and the laws of motionto develop these training procedures. Inthis chapter, you will learn how gravityaffects the motion of objects and how thelaws of motion apply to your

Forces and Motion CHAPTER


Imagine . . .

Chapter Starter TransparencyUse this transparency to help students begin thinking about forces and motion.

CHAPTER RESOURCESTechnology

Transparencies• Chapter Starter Transparency

Student Edition on CD-ROM

Guided Reading Audio CD• English or Spanish

Classroom Videos• Brain Food Video Quiz

Workbooks

Science Puzzlers, Twisters & Teasers• Forces and Motion g

READINGSKILLS

READING STRATEGY

Gravity and MotionSuppose you dropped a baseball and a marble at the same time from the top of a tall building. Which do you think would land on the ground fi rst?

In ancient Greece around 400 BCE, a philosopher named Aristo-tle (AR is TAWT uhl) thought that the rate at which an object fallsdepended on the object’s mass. If you asked Aristotle whetherthe baseball or the marble would land first, he would have saidthe baseball. But Aristotle never tried dropping objects withdifferent masses to test his idea about falling objects.

Gravity and Falling ObjectsIn the late 1500s, a young Italian scientist named GalileoGalilei (GAL uh LAY oh GAL uh LAY) questioned Aristotle’sidea about falling objects. Galileo argued that the mass of anobject does not affect the time the object takes to fall to theground. According to one story, Galileo proved his argumentby dropping two cannonballs of different masses from thetop of the Leaning Tower of Pisa in Italy. The people watch-ing from the ground below were amazed to see the two can-nonballs land at the same time. Whether or not this story istrue, Galileo’s work changed people’s understanding of gravityand falling objects.

1

Gravity and AccelerationObjects fall to the ground at the same rate becausethe acceleration due to gravity is the same for allobjects. Why is this true? Acceleration dependson both force and mass. A heavier object experi-ences a greater gravitational force than a lighterobject does. But a heavier object is also harderto accelerate because it has more mass. The extramass of the heavy object exactly balances the addi-tional gravitational force. Figure 1 shows objectsthat have different masses falling with the sameacceleration.

Figure 1 This stop-action photo shows that a table-tennis ball and a golf ball fall at the same rate even though they have different masses.

What You Will Learn

Explain the effect of gravity and airresistance on falling objects.Explain why objects in orbit are infree fall and appear to be weightless.Describe how projectile motion isaffected by gravity.

Vocabularyterminal velocityfree fallprojectile motion

Reading Organizer As you readthis section, create an outline of thesection. Use the headings from thesection in your outline.

OverviewIn this section, students learnhow gravity and air resistanceaffect falling objects. Studentsalso learn about orbiting andstudy the relationship betweengravity and projectile motion.You may wish to review the con-cepts of velocity, acceleration,and net force with your studentsbefore starting this section.

BellringerHave students write an answerto the following question: “IfWile E. Coyote and a boulderfall off a cliff at the same time,which do you think will hit theground first?”

Demonstration ---------------gFalling Objects Have studentsexamine a 12 in. softball and awomen’s-sized shot. Then, dis-cuss the objects’ similar sizesand different masses. Place aprotective board on the floor,and stand on a sturdy table.Tell students that you willdrop both objects from thesame height. Hold the objectsabove the board, and ask stu-dents to predict which willland first. Drop the objects atthe same time. Ask students fortheir observations, and repeatas necessary. l Visual

oVelocities of Falling Objects WhenGalileo attended the University of Pisain the 1500s, scholars generally acceptedAristotle’s theory that bodies fall to Earthat different velocities depending on theirmass. It is said that Galileo questionedAristotle’s teachings after observingdifferent-sized hailstones hitting theground at the same time.

1

CHAPTER RESOURCES

Chapter Resource File

CRF • Lesson Plan• Directed Reading Ab• Directed Reading Bs

Technology

Transparencies• Bellringer• P20 Falling Objects Accelerate at a Constant Rate

Workbooks

Interactive Textbook Struggling Readers Struggling Readers

Math Skills for Science• Arithmetic with Decimalsg


�v � 9.8 � 3 sm/ss

� 29.4 m/s

t ��vg

1st s4.9 m

2nd s14.7 m

3rd s24.5 m

v � 0 m/s downward




Acceleration Due to GravityAcceleration is the rate at which velocity changesover time. So, the acceleration of an object is theobject’s change in velocity divided by the amountof time during which the change occurs. All objectsaccelerate toward Earth at a rate of 9.8 meters persecond per second. This rate is written as 9.8 m/s/s,or 9.8 m/s2. So, for every second that an objectfalls, the object’s downward velocity increases by9.8 m/s, as shown in Figure 2.

✓Reading Check What is the acceleration due togravity? (See the Appendix for answers to Reading Checks.)

Velocity of Falling ObjectsYou can calculate the change in velocity (�v) of afalling object by using the following equation:

In this equation, g is the acceleration due to gravityon Earth (9.8 m/s2), and t is the time the objecttakes to fall (in seconds). The change in velocity isthe difference between the final velocity and thestarting velocity. If the object starts at rest, thisequation yields the velocity of the object after acertain time period.

Calculating the Velocity of Falling Objects A stoneat rest is dropped from a cliff, and the stonehits the ground after a time of 3 s. What is thestone’s velocity when it hits the ground?

Step 1: Write the equation for change invelocity.

�v � g � t

Step 2: Replace g with its value and t with thetime given in the problem, and solve.

To rearrange the equation to find time, divideby the acceleration due to gravity:

Now It’s Your Turn1. A penny at rest is dropped from the top

of a tall stairwell. What is the penny’svelocity after it has fallen for 2 s?

2. The same penny hits the ground in 4.5 s.What is the penny’s velocity as it hitsthe ground?

3. A marble at rest is dropped from a tallbuilding. The marble hits the groundwith a velocity of 98 m/s. How longwas the marble in the air?

4. An acorn at rest falls from an oak tree.The acorn hits the ground with a veloc-ity of 14.7 m/s. How long did it takethe acorn to land?

�v � g � t

Figure 2 A falling object accelerates ata constant rate. The object falls fasterand farther each second than it did thesecond before.

Using the Figure -----gSeeing Acceleration Draw stu-dents’ attention to Figures 1and 2. Be sure students under-stand that falling objects do notfall at a constant velocity butconstantly accelerate. Point outthat although the strobe imagesin Figure 1 were photographedat equal time intervals, the ballsmove faster and travel fartherduring each interval. l Visual

Answers to Math Focus

1. 9.8 m/s2 � 2 s � 19.6 m/sdownward

2. 9.8 m/s2 � 4.5 s � 44.1 m/sdownward

3. 98 m/s � 9.8 m/s2 � 10 s4. 14.7 m/s � 9.8 m/s2 � 1.5 sNote: To make these velocities moremeaningful to students, tell studentsthat 1 m/s is approximately 2.2 mi/h.So, 19.6 m/s is about 43 mi/h!

CONNECTIONCONNECTION vvMath ---------------------------------------------------------------------------g

Acceleration Due to GravityProblems Have students do thefollowing problems:

1. A boy standing on a high cliffdives into the ocean belowand strikes the water after3 s. What is the boy’s veloc-ity when he hits the water?(29.4 m/s downward)

2. A foul ball is hit straight up inthe air and falls from the topof its motion for 1.4 s beforebeing caught by the catcher.What is the velocity of theball as it hits the catcher’sglove? (13.72 m/s downward)

3. A brick falls from the topof a building and strikesthe ground with a velocityof 19.6 m/s downward. Howlong does the brick fall? (2 s)

l Logical

Answer to Reading Check

The acceleration due to gravity is 9.8 m/s2.CONNECTIONCONNECTION vvSocial Studies ------------------------a

Greek Letters The triangle in the symbolfor change in velocity is actually the Greekletter delta (�). In science, � often means“change in.” When used in front of a vari-able, such as velocity, it indicates the resultof subtracting the initial value of the vari-able from the final value of the variable.So, �v = vfinal � vinitial. Have students researchhow other Greek letters are used as symbolsin science. Students should summarizetheir findings in a poster. l Verbal

Section 1 • Gravity and Motion 151

Air Resistance and Falling ObjectsTry dropping two sheets of paper—one crumpled in a tightball and the other kept flat. What happened? Does this simpleexperiment seem to contradict what you just learned about fall-ing objects? The flat paper falls more slowly than the crumpledpaper because of air resistance. Air resistance is the force thatopposes the motion of objects through air.

The amount of air resistance acting on an object dependson the size, shape, and speed of the object. Air resistance affectsthe flat sheet of paper more than the crumpled one. The largersurface area of the flat sheet causes the flat sheet to fall slowerthan the crumpled one. Figure 3 shows the effect of air resis-tance on the downward acceleration of a falling object.

✓✓Reading Check Will air resistance have more effect on theacceleration of a falling leaf or the acceleration of a falling acorn?

Acceleration Stops at the Terminal VelocityAs the speed of a falling object increases, air resistance increases.The upward force of air resistance continues to increase untilit is equal to the downward force of gravity. At this point, thenet force is 0 N and the object stops accelerating. The objectthen falls at a constant velocity called the terminal velocity.terminal velocity.

Terminal velocity can be a good thing. Every year, cars,buildings, and vegetation are severely damaged in hailstorms.The terminal velocity of hailstones is between 5 and 40 m/s,depending on their size. If there were no air resistance,hailstones would hit the ground at velocities near 350 m/s!Figure 4 shows another situation in which terminal velocityis helpful.

Figure 4 Theparachute increasesthe air resistance ofthis sky diver andslows him to a safeterminal velocity.

The net force on the apple is equalto the force of air resistance sub-tracted from the force of gravity.Because the net force is not 0 N, theapple accelerates downward. But theapple does not accelerate as fast as itwould without air resistance.

The force of gravityis pulling down onthe apple. If gravitywere the only forceacting on the apple,the apple wouldaccelerate at a rateof 9.8 m/s2.

terminal velocityterminal velocity the constantvelocity of a falling object when theforce of air resistance is equal inmagnitude and opposite in directionto the force of gravity

Effect of Air Resistance on a Falling ObjectFigure 3

The force of air resistance is push-ing up on the apple. This force issubtracted from the force of gravity toyield the net force.

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READINGSTRATEGY -----------------g

Prediction Guide Before stu-dents read about air resistance,ask them to explain whether aschool bus or a racing car wouldbe affected less by air resistance.(a racing car, because a racingcar is built low to the ground,with smooth lines to reduceair resistance) l Verbal

CONNECTIONCONNECTION vvEarth Science ----------------------------g

Air Resistance and theAtmosphere Use the teachingtransparency titled “Layers ofthe Atmosphere” to discuss howair pressure decreases as altitudeincreases. As air pressure decreases,the potential for air resistancealso decreases. l Visual

CONNECTION toCONNECTION toHistory --------------------------------------------------g

First Parachutist The first per-son to use a parachute regularlywas French aeronaut André-Jacques Garnerin. He gave hisfirst demonstration of parachut-ing in Paris, France, in 1797.This first jump was from a bal-loon flying at height of about1,000 m (3,200 ft). Garnerintraveled around Europe todemonstrate his parachutingtechnique. In fact, during oneshow in England, Garnerinmade a jump from 2,440 m(8,000 ft)!


Transparencies• P21 Effect of Air Resistance on a Falling Object• LINK TOLINK TO EARTH SCIENCEEARTH SCIENCE E58 Layers of the

Atmosphere


Air resistance will have more of an effect onthe acceleration of a falling leaf.


Free Fall Occurs When There Is No Air ResistanceSky divers are often described as being in free fall before they open their parachutes. However, that is an incorrect description, because air resistance is always acting on the sky diver.

An object is in free fall only if gravity is pulling it down and no other forces are acting on it. Because air resistance is a force, free fall can occur only where there is no air. Two places that have no air are in space and in a vacuum. A vacuum is a place in which there is no matter. Figure 5 shows objects falling in a vacuum. Because there is no air resistance in a vacuum, the two objects are in free fall.

Orbiting Objects Are in Free FallLook at the astronaut in Figure 6. Why is the astronaut float-ing inside the space shuttle? You may be tempted to say that she is weightless in space. However, it is impossible for any object to be weightless anywhere in the universe.

Weight is a measure of gravitational force. The size of the force depends on the masses of objects and the distances between them. Suppose you traveled in space far away from all the stars and planets. The gravitational force acting on you would be very small because the distance between you and other objects would be very large. But you and all the other objects in the universe would still have mass. Therefore, gravity would attract you to other objects—even if just slightly—so you would still have weight.

Astronauts float in orbiting spacecrafts because of free fall. To better understand why astronauts float, you need to know what orbiting means.

Figure 5 Air resistance usually causes a feather to fall more slowly than an apple falls. But in a vacuum, a feather and an apple fall with the same acceleration because both are in free fall.

Figure 6 Astronauts appear to be weightless while they are floating inside the space shuttle—but they are not weightless!

free fall the motion of a body when only the force of gravity is acting on the body

StrategiesStrategiesINCLUSIONINCLUSION

• Learning Disabled• Attention Deficit Disorder• Behavior Control IssuesPlace items of different shapes and sizes on a table. Ask students to predict which items will be most affected by air resistance. Have student volunteers take turns drop-ping 2 or 3 items at the same time. Ask students to judge which items are affected the most by air resistance. Then, ask students to compare the shapes and sizes of the objects most affected by air resistance with the shapes and sizes of the objects least affected. l Visual

Using the Figure -----g

Partial Vacuums The strobe photo in Figure 5 shows a feather and an apple falling in a vacuum. Students may notice that the feather appears to be falling slower. In the top image, the feather is lined up with the bottom of the apple. In the bot-tom image, the feather is lined up with the top of the apple. Explain that it is impossible to create a total vacuum—especially in a chamber that is large enough to allow a feather and apple to fall side by side. Although the feather and the apple are not in a total vacuum, the photo shows that their accelerations in a partial vacuum are nearly equal. l Visual

vv -----------------------------------------b

The Meaning of a VacuumReview with students what a vacuum is (a space with no mat-ter). Point out that the partial vacuum in which the feather and apple were placed has almost no air left in it. There-fore, the feather cannot be affected very much by air resis-tance and will fall with almost the same acceleration as the apple. l Verbal

Is That a Fact!Air resistance is a result of friction between the falling object and the air and also the inertia of the particles of the air. The air particles have to “move out of the way” of the falling object. Because the particles have mass, they also have inertia. Therefore, the air particles resist movement.

When asked why he wasn’t interested in being a paratrooper, an Army pilot said, “I will never understand why anyone would want to jump out of a perfectly good airplane.” Ask students if they share the pilot’s opinion or if they might enjoy sky diving.


Two Motions Combine to Cause OrbitingAn object is orbiting when it is traveling around another object in space. When a spacecraft orbits Earth, it is moving forward. But the spacecraft is also in free fall toward Earth. Figure 7shows how these two motions combine to cause orbiting.

As you can see in Figure 7, the space shuttle is always falling while it is in orbit. So why don’t astronauts hit their heads on the ceiling of the falling shuttle? Because they are also in free fall—they are always falling, too. Because astronauts are in free fall, they float.

Orbiting and Centripetal ForceBesides spacecrafts and satellites, many other objects in the universe are in orbit. The moon orbits the Earth. Earth and the other planets orbit the sun. In addition, many stars orbit large masses in the center of galaxies. Many of these objects are traveling in a circular or nearly circular path. Any object in circular motion is constantly changing direction. Because an unbalanced force is necessary to change the motion of any object, there must be an unbalanced force working on any object in circular motion.

The unbalanced force that causes objects to move in a cir-cular path is called a centripetal force (sen TRIP uht uhl FOHRS).Gravity provides the centripetal force that keeps objects in orbit. The word centripetal means “toward the center.” As you can see in Figure 8, the centripetal force on the moon points toward the center of the moon’s circular orbit.

✓Reading Check What does the word centripetal mean?

Figure 8 The moon stays in orbit around Earth because Earth’s gravitational force provides a centripetal force on the moon.

Path of moon

Centripetalforce on the moon

How an Orbit Is FormedFigure 7

The space shuttle moves forward at a constant speed. If there were no gravity, the space shuttle would follow the path of the dotted line.

The path of the space shuttle follows the curve of Earth’s surface. Following this path is known as orbiting.

The space shuttle is in free fall because gravity pulls it toward Earth. The space shuttle would move straight down if it were not traveling forward.

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Using the Figure -----gHow an Orbit is Formed Draw students’ attention to Figure 7.Ask students why the shuttle does not fall to Earth if gravity is pulling downward on it. (The for-ward motion of the shuttle occurs together with free fall to produce a path that follows the curve of Earth’s surface.) Ask what would happen if the shuttle started moving much faster or much slower. (Ifthe shuttle moved fast enough, it would escape Earth’s gravitational force and move off into space. If the shuttle moved more slowly, it would begin to fall toward Earth. Note: Tell students that the shuttle slows down to land in a controlled “fall” toward Earth. However, the shuttle continues to move forward so it spi-rals down toward Earth rather than falling straight down.) l Visual

CulturalAwarenessCulturalAwareness g

An Astronaut First OnSeptember 12, 1992, Dr. Mae Jemison became the first African-American woman to orbit Earth. She was a science mission specialist on the space shuttle Endeavour.Dr. Jemison, who has degrees in chemical engineering and medicine, was in charge of many of the experiments con-ducted during the mission.


The word centripetal means “toward the center.” CONNECTIONCONNECTION vv

Astronomy --------------------------------------------a

Scale Drawing In Figure 8, the relative sizes of Earth and the moon and the dis-tance between the two are not drawn to scale. Ask students to find average distance between Earth and the moon and the diameters of Earth and the moon. Then, have students use this information to make a poster of the moon in orbit around Earth that is drawn to scale. l Logical/Visual

MISCONCEPTIONALERT

Shuttle Orbit The shuttle in Figure 7is shown in orbit facing forward and oriented right side up (called airplanemode). In orbit, the shuttle spends most of the time upside down and backward. It also orbits upside down and sideways (wing first), but it rarely orbits in air-plane mode. It is only in airplane mode for landings.

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Projectile Motion and GravityThe motion of a hopping grasshopper is an example of pro-jectile motion (proh JEK tuhl MOH shuhn). Projectile motionis the curved path an object follows when it is thrown orpropelled near the surface of the Earth. Projectile motion hastwo components—horizontal motion and vertical motion. Thetwo components are independent, so they have no effect oneach other. When the two motions are combined, they form acurved path, as shown in Figure 9. Some examples of projectilemotion include the following:

• a frog leaping

• water sprayed by a sprinkler

• a swimmer diving into water

• balls being juggled

• an arrow shot by an archer

Horizontal MotionWhen you throw a ball, your hand exerts a force on the ballthat makes the ball move forward. This force gives the ball itshorizontal motion, which is motion parallel to the ground.

After you release the ball, no horizontal forces are actingon the ball (if you ignore air resistance). Even gravity doesnot affect the horizontal component of projectile motion. So,there are no forces to change the ball’s horizontal motion.Thus, the horizontal velocity of the ball is constant after theball leaves your hand, as shown in Figure 9.

projectile motion the curved paththat an object follows when thrown,launched, or otherwise projectednear the surface of Earth

The ball’s verticalvelocity increasesbecause gravitycauses it to accel-erate downward. The two motions

combine to forma curved path.

After the ball leaves the pitcher’s hand, theball’s horizontal velocity is constant.

Projectile MotionFigure 9

CONNECTIONCONNECTION vvMath -----------------------------------------------------------a

Vectors Vectors are mathemati-cal tools that are often usedin physics. Vectors look likearrows. The length of thevector indicates magnitudeand the orientation of the vectorshows direction. For example,vectors are often used to repre-sent velocity. The yellow arrowsin Figure 9 are velocity vectors.The long horizontal vector rep-resents a large velocity to theright. The vertical vectors showincreasing velocity downward.Encourage interested studentsto learn about vectors. Havethem make a poster showinghow vectors can be added andsubtracted. l Logical


Transparencies• P22 How an Orbit Is Formed; Projectile Motion

SUPPORT FOR

English LanguageLearnersCentripetal Force andProjectile Motion To rein-force the difference betweencentripetal force and projec-tile motion, demonstrate witha small rubber ball attached toa long rubber band. Hold therubber band in front of younear the end and swing theball. Tell students that the ballis “orbiting” your fingers. Askthem if this shows centripetalforce or projectile motion(centripetal force). Then,hold the end of the rubberband and toss the ball under-handed straight ahead. Ask ifthis shows centripetal force orprojectile motion (projectilemotion). Have volunteersexplain how they know thedifference. Prompt studentswith references to the text.l Visual/Verbal


Vertical MotionGravity pulls everything on Earth downward toward the center of Earth. A ball in your hand is prevented from falling by your hand. After you throw the ball, gravity pulls it downward and gives the ball vertical motion. Vertical motion is motion that is perpendicular to the ground. Gravity pulls objects in projectile motion down at an acceleration of 9.8 m/s2 (if air resistance is ignored). This rate is the same for all falling objects. Figure 10shows that the downward acceleration of a thrown object and a falling object are the same.

Because objects in projectile motion accelerate downward, you always have to aim above a target if you want to hit it with a thrown or propelled object. That’s why when you aim an arrow directly at a bull’s-eye, your arrow strikes the bottom of the target rather than the middle of the target.

✓Reading Check What gives an object in projectile motion its vertical motion?

Penny Projectile Motion1. Position a flat ruler and two pennies on a

desk or table as shown below.

2. Hold the ruler by the end that is on the desk. Move the ruler quickly in the direction shown so that the ruler knocks the penny off the table and so that the other penny also drops. Repeat this step several times.

3. Which penny travels with projectile motion? In what order do the pennies hit the ground? Record and explain your answers.

Projectile Motion and Acceleration Due to GravityFigure 10

The yellow ball was given a horizontal push off the ledge and fol-lows projectile motion.

The balls have the same acceleration due to gravity. The horizontal motion of the yellow ball does not affect its vertical motion.

The red ball was droppedwithout a horizontalpush.

For another activity related to this chapter, go to go.hrw.com and type in the keyword HP5FORW.



Gravity gives vertical motion to an object in projectile motion.

Reteaching -------------------------------------b

Horizontal Velocity Give stu-dents photocopies of Figure 10and ask them to use a ruler to draw vertical lines through the centers of the yellow balls. Then, have students measure the distance between the lines. Students should find that the distances are equal. Explain that this fact shows that the horizon-tal velocity is constant. l Visual

Quiz ---------------------------------------------------------------------g

1. Why do you have to aim above a target that you want to hit with a thrown object? (The thrown object will be in pro-jectile motion and will therefore accelerate downward.)

2. When does an object reach its terminal velocity? (when the upward force of air resistance equals the downward force of gravity)

Alternative Assessment ---------------------------g

Making Models Give each group a plastic bag, string, tape, a washer, scissors, and a stop-watch. Have each group design a parachute. Challenge the groups to make the parachute that descends the slowest. How does the design of a parachute affect its rate of fall? l Kinesthetic

M A T E R I A L SFOR EACH GROUP

• pennies (2)• ruler, flat

Teacher’s Notes: Make sure students have plenty of room. The penny in pro-jectile motion may travel 1–2 m from its starting point. If the Quick Lab is done in a room without a carpet, students can listen for the sound of the pennies

hitting the floor. Students should move the ruler quickly enough so that the penny on the ruler drops straight down.

Answers

3. The penny that was knocked off the table with the ruler was in projectile motion. The pennies should land at the same time because they have the same acceleration due to gravity. The horizontal motion does not affect the vertical motion.

For a variety of links related to thischapter, go to www.scilinks.org

SummarySummary

Review

Using Key Terms

1. Use each of the following terms in a separatesentence: terminal velocity and free fall.

Understanding Key Ideas

2. Which of the following is in projectile motion?

a. a feather falling in a vacuumb. a cat leaping on a toyc. a car driving up a hilld. a book laying on a desk

3. How does air resistance affect the accelerationof falling objects?

4. How does gravity affect the two components ofprojectile motion?

5. How is the acceleration of falling objectsaffected by gravity?

6. Why is the acceleration due to gravity the samefor all objects?

Math Skills

7. A rock at rest falls off a tall cliff and hits thevalley below after 3.5 s. What is the rock’svelocity as it hits the ground?

Critical Thinking

8. Applying Concepts Think about a sport thatuses a ball. Identify four examples from thatsport in which an object is in projectile motion.

• Gravity causes all objects to acceleratetoward Earth at a rate of 9.8 m/s2.

• Air resistance slows the acceleration offalling objects. An object falls at its termi-nal velocity when the upward force of airresistance equals the downward force ofgravity.

• An object is in free fall if gravity is the onlyforce acting on it.

• Objects in orbit appear to be weightlessbecause they are in free fall.

• A centripetal force is needed to keepobjects in circular motion. Gravity acts as acentripetal force to keep objects in orbit.

• Projectile motion is the curved path anobject follows when thrown or propellednear the surface of Earth.

• Projectile motion has two components—horizontal motion and vertical motion.Gravity affects only the vertical motion ofprojectile motion.

9. Making Inferences The moon has no atmo-sphere. Predict what would happen if an astro-naut on the moon dropped a hammer and afeather at the same time from the same height.

Interpreting Graphics

10. Whenever Jon delivers a newspaper to theZapanta house, the newspaper lands in thebushes, as shown below. What should Jon do tomake sure the newspaper lands on the porch?

Topic: Gravity and Orbiting Objects;Projectile Motion

SciLinks code: HSM0692; HSM1223

Answers to Section Review

1. Sample answers: The skydiver stopped acceleratingdownward because shereached her terminal velocity.A feather dropped on the moonis in free fall.

2. b3. Air resistance reduces the

acceleration of falling objectsand causes them to fall moreslowly.

4. Gravity has no effect on thehorizontal component of pro-jectile motion. Gravity changesthe vertical component of pro-jectile motion by acceleratingan object downward.

5. The acceleration due togravity is the same for allobjects. (Note: This is true onlynear the surface of Earth andwhen no air resistance acts onthe objects.) Also acceptable:The force of gravity causes theacceleration of falling objects.

6. A heavier object experiencesa greater gravitational forcethan a lighter object does. Buta heavier object is also harderto accelerate because it hasmore mass. The greater gravi-tational force is exactly bal-anced by the greater mass.So, all objects fall with thesame acceleration.

7. 3.5 s � 9.8 m/s2 � 34.3 m/s8. Sample answer: Basketball:

a player jumping to dunk theball, a ball passed betweenplayers, a ball shot toward thebasket, and a ball bounced onthe floor before it hits the floor

9. The feather and the hammerwould hit the moon’s surface atthe same time because there isno air resistance. The featherand the hammer are in free fall.

10. Jon should either aim higherwhen throwing the newspaperor he should throw the news-paper with a greater horizontalvelocity.

CHAPTER RESOURCES


• Section Quizg• Section Reviewg• Vocabulary and Section Summaryg• Reinforcement Worksheetb• Datasheet for Quick Lab

Technology

Interactive Explorations CD-ROM• Extreme Skiingg

CRF


READING STRATEGY

Newton’s Laws of MotionImagine that you are playing baseball. The pitch comes in, and—crack—you hit the ball hard! But instead of fl ying off the bat, the ball just drops to the ground. Is that normal?

You would probably say no. You know that force and motionare related. When you exert a force on a baseball by hitting itwith a bat, the baseball should move. In 1686, Sir Isaac Newtonexplained this relationship between force and the motion ofan object with his three laws of motion.

Newton’s First Law of Motion

An object at rest remains at rest, and an object in motion remains in motion at constant speed and in a straight line unless acted on by an unbalanced force.

Newton’s first law of motion describes the motion of an objectthat has a net force of 0 N acting on it. This law may seemcomplicated when you first read it. But, it is easy to understandwhen you consider its two parts separately.

Part 1: Objects at RestAn object that is not moving is said to be at rest. A chair onthe floor and a golf ball balanced on a tee are examples ofobjects at rest. Newton’s first law says that objects at rest willstay at rest unless they are acted on by an unbalanced force.For example, objects will not start moving until a push ora pull is exerted on them. So, a chair won’t slide across theroom unless you push the chair. And, a golf ball won’t moveoff the tee unless the ball is struck by a golf club, as shownin Figure 1.

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Figure 1 A golf ball will remain at rest on a tee until it is acted on by the unbalanced force of a moving club.

Unbalanced forceObject at rest

Object in motion

What You Will Learn

Describe Newton’s first law ofmotion, and explain how it relates toobjects at rest and objects in motion.State Newton’s second law ofmotion, and explain the relationshipbetween force, mass, and accelera-tion.State Newton’s third law of motion,and give examples of force pairs.

Vocabularyinertia

Paired Summarizing Read thissection silently. In pairs, take turnssummarizing the material. Stop todiscuss ideas that seem confusing.

OverviewThis section introduces studentsto Newton’s laws of motion.Before teaching this section, youmay wish to review the conceptsof acceleration, force, net force,friction, and balanced andunbalanced forces with yourstudents.

BellringerHave students respond to thefollowing question:

If you are sitting still in yourseat on a bus that is travelingon a highway, is your body atrest or in motion? (in motionwith respect to the ground)

Explain your answer. Use a dia-gram if it will help make youranswer clear.

Demonstration --------------gEgg in a Buggy Place a hard-boiled egg in a small, wheeledcart. Apply a strong force to thecart so that it strikes a wall. Askstudents to draw a series of pic-tures that show what happens tothe egg as the cart moves acrossthe floor and strikes the wall.Then, ask them to draw a pic-ture of how the egg could beprotected in the cart. Challengestudents to explain what hap-pened to the egg. l Visual

CONNECTION toCONNECTION toHistory --------------------------------------------------g

Sir Isaac Newton Long before Newton,others had observed relationships betweenforces and motion, rest, and acceleration.When Newton extended their work withhis three laws of motion, he said, “If I haveseen further it is by standing on the shoul-ders of Giants.” Newton’s genius was thathe combined previous discoveries plus hisown observations into a unified picture ofhow the universe worked.

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CHAPTER RESOURCES


CRF • Lesson Plan • Directed Reading Ab • Directed Reading Bs

Technology

Transparencies• Bellringer

Workbooks

Interactive Textbook Struggling ReadersStruggling Readers


Part 2: Objects in MotionThe second part of Newton’s first law is about objects moving with a certain velocity. Such objects will continue to move forever with the same velocity unless an unbalanced force acts on them.

Think about driving a bumper car at an amusement park. Your ride is pleasant as long as you are driving in an open space. But the name of the game is bumper cars! Sooner or later you are likely to run into another car, as shown in Figure 2. Your bumper car stops when it hits another car. But, you continue to move forward until the force from your seat belt stops you.

Figure 2 Bumper cars let you have fun with Newton’s first law.

First Law Skateboard1. Place an empty soda can on top of a skate-

board.2. Ask a friend to catch the skateboard after you

push it. Now, give the skateboard a quick, firm push. What happened to the soda can?

3. Put the can on the skateboard again. Push the skateboard gently so that the skateboard moves quickly but so that the can does not fall.

4. Ask your friend to stop the skateboard after he or she allows it to travel a short distance. What happened to the can?

5. Explain how Newton’s first law applies to what happened.

Friction and Newton’s First LawAn object in motion will stay in motion forever unless it is acted on by an unbalanced force. So, you should be able to give your desk a push and send it sliding across the floor. If you push your desk, the desk quickly stops. Why?

There must be an unbalanced force that acts on the desk to stop its motion. That unbalanced force is friction. The friction between the desk and the floor works against the motion of the desk. Because of friction, observing the effects of Newton’s first law is often difficult. For example, friction will cause a rolling ball to slow down and stop. Friction will also make a car slow down if the driver lets up on the gas pedal. Because of friction, the motion of objects changes.

✓Reading Check When you ride a bus, why do you fall forward when the bus stops moving? (See the Appendix for answers to Reading Checks.)

An unbalanced force from another car acts on your car and changes your car’s motion.

a

The collision changes your car’s motion, not your mo-tion. Your motion continues with the same velocity.

b

Another unbalanced force, from your seat belt, changes your motion.

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When the bus is moving, both you and the bus are in motion. When the bus stops moving, no unbalanced force acts on your body, so your body continues to move forward.

Is That a Fact!Antilock braking systems (ABS) con-trolled by a computer prevent skidding by sensing when the wheels are about to lock. They release and reapply the brakes up to 25 times a second. Instead of skidding out of control, the car slows down and stops safely.

CONNECTIONCONNECTION vvReal World ---------------------------------------------g

Preventing Jackknifes A trac-tor trailer will often jackknife on an icy road when the driver suddenly applies the brakes. The brakes are applied to the tractor wheels and the front part of the rig (the tractor) stops. However, the back half (the trailer) skids and continues moving in accor-dance with Newton’s first law, causing the rig to jackknife. Ask students to speculate on how jackknife accidents might be prevented. l Verbal

M A T E R I A L SFOR EACH GROUP

• skateboard• soda can, empty

Teacher’s Note: Ask your students to bring their skate-boards to school if they have them. If you do not have enough skateboards, you can use other wheeled objects or use empty film canisters on toy cars.

Answers

2. The soda can should fall over after the push.

4. The can should fall over when the skateboard is stopped.

5. In step 2, the skateboard and the can were at rest. When you pushed the skateboard with an unbalanced force, the skateboard started to move. But, no unbalanced force acted on the can, so it fell over backward when the skateboard moved under it. In step 4, the skateboard was stopped by an unbalanced force. But no unbalanced force acted on the can, so it remained in motion and fell over forward.

Section 2 • Newton’s Laws of Motion 159

Inertia and Newton’s First LawNewton’s first law of motion is sometimes called thelaw of inertia. InertiaInertia (in UHR shuh) is the tendency ofall objects to resist any change in motion. Because ofinertia, an object at rest will remain at rest until a forcemakes it move. Likewise, inertia is the reason a movingobject stays in motion with the same velocity unless aforce changes its speed or direction. For example, becauseof inertia, you slide toward the side of a car when thedriver turns a corner. Inertia is also why it is impossiblefor a plane, car, or bicycle to stop immediately.

Mass and InertiaMass is a measure of inertia. An object that has a smallmass has less inertia than an object that has a largemass. So, changing the motion of an object that hasa small mass is easier than changing the motion of anobject that has a large mass. For example, a softball hasless mass and therefore less inertia than a bowling ball.Because the softball has a small amount of inertia, it iseasy to pitch a softball and to change its motion by hit-ting it with a bat. Imagine how difficult it would be toplay softball with a bowling ball! Figure 3 further showsthe relationship between mass and inertia.

Figure 3 Inertia makes it harder to accelerate a car than to accelerate a bicycle. Inertia also makes it easier to stop a moving bicycle than a car moving at the same speed.

inertiainertia the tendency of an object to resist being moved or, if the object is moving, to resist a change in speed or direction until an outside force acts on the object

First-Law Magic1. On a table or desk ,

place a large, empty plastic cup on top of a paper towel.

2. Without touching the cup or tipping it over, remove the paper towel from under the cup. How did you accomplish this? Repeat this step.

3. Fill the cup half full with water, and place the cup on the paper towel.

4. Once again, remove the paper towel from under the cup. Was it easier or harder to do this time?

5. Explain your observations in terms of mass, inertia, and Newton’s first law of motion.

M A T E R I A L SFOR EACH STUDENT

• paper towel or construction paper

• plastic cup, empty• water

Teacher’s Notes: Cupsshould be large (12 oz ormore), or 500 mL plastic bea-kers can be used.

Make sure that students don’tfill the cups more than half-way. This will reduce spills,but it still makes the cupnoticeably more massive.

Instruct students to keep theouter surfaces of the cups dry.A wet paper towel may breakwhen pulled.

Beans or popcorn kernels canbe substituted for the water,if desired.

Be sure to have extra papertowels on hand to clean upany spilled water.

Answers

2. Students will quickly learn thatthey have to jerk the papertowel out from under the cup,as in a magic trick.

5. It should be easier for studentsto do the trick with water in thecup because the cup has moremass and therefore more iner-tia. When the cup has moreinertia, it is harder to move. Itis therefore easier to move thepaper towel out from under it. CHAPTER RESOURCES

Technology

Transparencies• P23 Mass, Force, and Acceleration


Acceleration Acceleration Acceleration

Newton’s Second Law of Motion

The acceleration of an object depends on the mass ofthe object and the amount of force applied.

Newton’s second law describes the motion of an object whenan unbalanced force acts on the object. As with Newton’s firstlaw, you should consider the second law in two parts.

Part 1: Acceleration Depends on MassSuppose you are pushing an empty cart. You have to exert onlya small force on the cart to accelerate it. But, the same amountof force will not accelerate the full cart as much as the emptycart. Look at the first two photos in Figure 4. They show thatthe acceleration of an object decreases as its mass increasesand that its acceleration increases as its mass decreases.

Part 2: Acceleration Depends on ForceSuppose you give the cart a hard push, as shown in the thirdphoto in Figure 4. The cart will start moving faster than if yougave it only a soft push. So, an object’s acceleration increases asthe force on the object increases. On the other hand, an object’sacceleration decreases as the force on the object decreases.

The acceleration of an object is always in the same direc-tion as the force applied. The cart in Figure 4 moved forwardbecause the push was in the forward direction.

✓Reading Check What is the relationship between the force onan object and the object’s acceleration?

If the force applied to the carts is the same,the acceleration of the empty cart is greaterthan the acceleration of the loaded cart.

Acceleration will increase whena larger force is exerted.

Car Sizes and PollutionOn average, newer cars pol-lute the air less than older carsdo. One reason for this is thatnewer cars have less massthan older cars have. An objectthat has less mass requiresless force to achieve the sameacceleration as an object thathas more mass. So, a small carcan have a small engine andstill have good acceleration.Because small engines use lessfuel than large engines use,small engines create less pol-lution. Research three modelsof cars from the same year,and make a chart to comparethe mass of the cars with theamount of fuel they use.

Mass, Force, and AccelerationFigure 4

StrategiesStrategiesINCLUSIONINCLUSION

• Hearing Impaired• Learning Disabled• Attention Deficit DisorderExplore some examplesof forces that will cause anobject at rest to move. Placetwo plastic bowls and awooden board on a desk. Theboard should be about 2 ftlong. Write the followingactions on slips of paper:

• Flick a bowl by using yourthumb and forefinger.

• Slap a bowl with your openhand.

• Blow on the side of a bowl.

• Shove a second bowl so thatit bumps into the first bowl.

• Put a bowl on the left end ofthe board. Lift the left endof the board 4 in. upward.



Ask different students to per-form each action. Discuss theresults. l Kinesthetic


The acceleration of an object increases as theforce exerted on the object increases. (Note:this assumes that the mass of the object isconstant.)

There once was a trucker from Nome,

Whose rig was loaded with foam.

Its very small mass

Made him able to pass

The other trucks all the way home.

SUPPORT FOR

English LanguageLearnersNewton’s Second LawFor practice in careful read-ing, have students read onlythe statement of Newton’ssecond law of motion and,then, write the law in their ownwords. They may use dictionar-ies to look up words or drawdiagrams to clarify their ideas.After students have read thesection on the second law, havestudents orally compare whatthey wrote with what they havelearned. Call on students to en-sure full participation.l Verbal


a � � 9.8 m/s210 kg•m/s2

1.02 kg

a � � 9.8 m/s21 kg•m/s2

0.102 kg

1 N � 1 kg•m/s2

Expressing Newton’s Second Law MathematicallyThe relationship of acceleration (a) to mass (m) and force (F) can be expressed mathematically with the following equation:

Notice that the equation can be rearranged to find the force applied. Both forms of the equation can be used to solve problems.

Newton’s second law explains why objects fall to Earth with the same acceleration. In Figure 5, you can see how the large force of gravity on the watermelon is offset by its large mass. Thus, you find that the accelerations of the watermelon and the apple are the same when you solve for acceleration.

a � , or F � m � aFm

Second-Law Problems What is the acceleration of a 3 kg mass if a force of 14.4 N is used to move the mass? (Note: 1 N is equal to 1 kg•m/s2)

Step 1: Write the equation for acceleration.

Step 2: Replace F and m with the values given in the problem, and solve.

Now It’s Your Turn1. What is the acceleration of a 7 kg mass

if a force of 68.6 N is used to move it toward Earth?

2. What force is necessary to accelerate a 1,250 kg car at a rate of 40 m/s2?

3. Zookeepers carry a stretcher that holds a sleeping lion. The total mass of the lion and the stretcher is 175 kg. The lion’s forward acceleration is 2 m/s2.What is the force necessary to produce this acceleration?

The apple has less mass than the watermelon does. So, less force is needed to give the apple the same acceleration that the watermelon has.

Newton’s Second Law and Acceleration Due to GravityFigure 5

a �Fm

a � � 4.8 m/s214.4 kg•m/s2

3 kg

m � 1.02 kg

F � 10 N

10 N � 10 kg •m/s2

m � 0.102 kg

F � 1 N

Discussion ----------------------------------aRearranging Newton’s Second Law Discuss with students how the equation F � m � a can be used to find the mass of an object. Have them imagine that they hit an object of unknown mass with a force of 15 N and that the object accelerates at 5 m/s2. What is the mass of the object? (3 kg) l Logical

CONNECTION toCONNECTION toMath ---------------------------------------------------------------b

Evaluating the Equation When you introduce the equation for Newton’s second law, point out to students that acceleration and force are directly proportional (as force increases, acceleration increases) and that acceleration and mass are inversely pro-portional (as mass increases, acceleration decreases). These relationships are explained qualitatively, but students may not see the connection on their own. Also remind students of the definition of a newton:

1 newton � 1 kilogram-meter per second per second

OR

1 N � 1 kg•m/s2

This is important for helping students through the unit can-cellation in the Math Focus and in Figure 5.

CONNECTIONCONNECTION vvMath ---------------------------------------------------------------------------g

More Second Law Problems Have stu-dents do the following problems:

• Calculate the gravitational force acting on your 6 kg backpack. (This force is the weight of your backpack.) (F � 6 kg � 9.8 m/s2 � 58.8 N)

• A 50 kg skater pushes off from a wall with a force of 200 N. What is the skater’s acceleration? (a � 200 N � 50 kg �200 kg•m/s2 � 50 kg � 4 m/s2)l Logical


1. a � F � m � 68.6 N � 7 kg �9.8 m/s2 (This is acceleration due to gravity.)

2. F � m � a � 1,250 kg � 40 m/s2 � 50,000 N3. F � m � a � 175 kg � 2 m/s2 � 350 N



Newton’s Third Law of Motion

Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.

Newton’s third law can be simply stated as follows: All forces act in pairs. If a force is exerted, another force occurs that is equal in size and opposite in direction. The law itself addresses only forces. But the way that force pairs interact affects the motion of objects.

How do forces act in pairs? Study Figure 6 to learn how one force pair helps propel a swimmer through water. Action and reaction force pairs are present even when there is no motion. For example, you exert a force on a chair when you sit on it. Your weight pushing down on the chair is the action force. The reaction force is the force exerted by the chair that pushes up on your body. The force is equal to your weight.

✓Reading Check How are the forces in each force pair related?

Force Pairs Do Not Act on the Same ObjectA force is always exerted by one object on another object. This rule is true for all forces, including action and reaction forces. However, action and reaction forces in a pair do not act on the same object. If they did, the net force would always be 0 N and nothing would ever move! To understand how action and reaction forces act on objects, look at Figure 6 again. The action force was exerted on the water by the swimmer’s hands. But the reaction force was exerted on the swimmer’s hands by the water. The forces did not act on the same object.

Figure 6 The action force and reaction force are a pair. The two forces are equal in size but opposite in direction.

Newton BallPlay catch with an adult. As you play, discuss how Newton’s laws of motion are involved in the game. After you finish your game, make a list in your science journal of what you discussed.

The action force is the swimmer’shands pushing on the water.

The reaction force is the water push-ing on the hands. The reaction force moves the swimmer forward.

CHAPTER RESOURCESWorkbooks

Math Skills for Science • Newton: Force and Motion g

Discussion ----------------------------------g

Newton’s Third Law and Spacewalking Underwater training to simulate spacewalk-ing is a major part of astronaut training. Discuss with students what would happen to astro-nauts in space who forget Newton’s third law of motion as they tried to work on a spacecraft. (Sample answers: The spacecraft would seem to repel the astronauts every time they touched it because each touch is a small force.) l Verbal

CONNECTIONCONNECTION vvLife Science -----------------------------------g

Squid Propulsion Ask students to find out how a squid propels itself through the water and to explain the squid’s movement using Newton’s third law. Have students make a poster or do a presentation to demonstrate what they have learned about squid propulsion. l Visual/Verbal

h--------------------------------b

PORTFOLIO

Poster Project Ask stu-dents to find several

magazine pictures of sporting events. Have students identify the action-reaction force pairs in each picture. l Visual


Action and Reaction Study Figures 6 and 7 in this section with students. Be sure they understand that in any force pair, the distinction between the action and reaction force is arbitrary. It doesn’t matter which force we call the action and which force we call the reaction. l Visual


The forces in a force pair are equal in size and opposite in direction.

CONNECTION toCONNECTION toReal World -----------------------------------g

Artillery Recoil Newton’s third law explains that when a shell is fired from an artillery piece, the force opposite to that which propels the shell forward causes the gun to recoil, or move backward. Because the mass of the gun is so much greater than the mass of the shell, the shell moves forward with a far greater velocity than the gun moves backward. This same law applies to the human cannonball at the circus!

Action force

Reaction force

All Forces Act in Pairs—Action and ReactionNewton’s third law says that all forces act in pairs. When aforce is exerted, there is always a reaction force. A force neveracts by itself. Figure 7 shows some examples of action and reac-tion force pairs. In each example, the action force is shownin yellow and the reaction force is shown in red.

The Effect of a Reaction Can Be Difficult to SeeAnother example of a force pair is shown in Figure 8. Gravityis a force of attraction between objects that is due to theirmasses. If you drop a ball, gravity pulls the ball toward Earth.This force is the action force exerted by Earth on the ball. Butgravity also pulls Earth toward the ball. The force is the reac-tion force exerted by the ball on Earth.

It’s easy to see the effect of the action force—the ball fallsto Earth. Why don’t you notice the effect of the reactionforce—Earth being pulled upward? To find the answer to thisquestion, think about Newton’s second law. It states that theacceleration of an object depends on the force applied to it andon the mass of the object. The force on Earth is equal to theforce on the ball. But the mass of Earth is much larger thanthe mass of the ball. Thus, the acceleration of Earth is muchsmaller than the acceleration of the ball. The acceleration ofthe Earth is so small that you can’t see or feel the accelera-tion. So, it is difficult to observe the effect of Newton’s thirdlaw on falling objects.

Why do objects fall toward Earth?

Figure 8 The force of gravitybetween Earth and a fallingobject is a force pair.

The rabbit’s legs exert aforce on Earth. Earth exertsan equal force on therabbit’s legs and causes therabbit to accelerate upward.

The bat exerts a force on theball and sends the ball fly-ing. The ball exerts an equalforce on the bat, but the batdoes not move backwardbecause the batter is exert-ing another force on the bat.

The space shuttle’sthrusters push theexhaust gases down-ward as the gases pushthe shuttle upwardwith an equal force.

Examples of Action and Reaction Force PairsFigure 7

✓Reading Check

Reteaching -------------------------------------bSecond-Law Practice Havestudents demonstrate the rela-tionships between mass, force,and acceleration by pushing awheeled cart with differentforces. Change the mass of thecart by placing heavy books onthe cart. Ask the class to describethe accelerations they observed.l Kinesthetic

Quiz ---------------------------------------------------------------------g

1. How does Newton’s secondlaw explain why it is easierto push a bicycle than to pusha car with the same accelera-tion? (The bicycle has a smallermass, so a smaller force isrequired to give it the sameacceleration as the car.)

2. Use Newton’s third law toexplain how a rocket acceler-ates. (The hot gases expelledfrom the back of the rocket pro-duce a reaction force on therocket that accelerates it.)

AlternativeAssessment ---------------------------g

Writing Story Have studentswrite a story about anastronaut who spacewalks

to fix a satellite. The only itemsshe is carrying are her tools. Asshe completes the job, her back-pack rocket fails. In the story,students should explain how theastronaut returns to the space-craft. (Using Newton’s third law,she could move toward the space-craft by throwing her tools awayfrom the spacecraft.) l Verbal


Objects accelerate toward Earth becausethe force of gravity pulls them toward Earth.

CulturalAwarenessCulturalAwareness g

Gunpowder The Chinese inventedgunpowder by the 10th century andused it in rockets for fireworks. Theserockets were later adapted to warfare.In the 13th century, Chinese armieslaunched rockets over enemy troops.



SummarySummary

Review

• Newton’s first law of motion states that themotion of an object will not change if nounbalanced forces act on it.

• Objects at rest will not move unless actedupon by an unbalanced force.

• Objects in motion will continue to moveat a constant speed and in a straight lineunless acted upon by an unbalanced force.

• Inertia is the tendency of matter to resista change in motion. Mass is a measure ofinertia.

• Newton’s second law of motion states thatthe acceleration of an object depends onits mass and on the force exerted on it.

• Newton’s second law is represented by thefollowing equation: F � m � a.

• Newton’s third law of motion states thatwhenever one object exerts a force on asecond object, the second object exertsan equal and opposite force on the firstobject.

Using Key Terms

1. In your own words, write a definition for theterm inertia.


2. Which of the following will increase the accel-eration of an object that is pushed by a force?

a. decreasing the mass of the objectb. increasing the mass of the objectc. increasing the force pushing the objectd. Both (a) and (c)

3. Give three examples of force pairs that occurwhen you do your homework.

4. What does Newton’s first law of motion sayabout objects at rest and objects in motion?

5. Use Newton’s second law to describe the rela-tionship between force, mass, and acceleration.

Math Skills

6. What force is necessary to accelerate a 70 kgobject at a rate of 4.2 m/s2?

Critical Thinking

7. Applying Concepts When a truck pulls atrailer, the trailer and truck accelerate forwardeven though the action and reaction forces arethe same size but are in opposite directions.Why don’t these forces balance each other?

8. Making Inferences Use Newton’s first lawof motion to explain why airbags in cars areimportant during head-on collisions.

Interpreting Graphics

9. Imagine you accidentally bumped your handagainst a table, as shown in the photo below.Your hand hurts after it happens. Use Newton’sthird law of motion to explain what causedyour hand to hurt.

Topic: Newton’s Laws of MotionSciLinks code: HSM1028


1. Sample answer: Inertia is thetendency of an object to resistchanges in motion.

2. d3. Accept all reasonable answers.

Students should list three exam-ples of force pairs. Partial sam-ple answer: using a pencil or pen(action: hand pushing on pencil;reaction: pencil pushing back onhand OR action: pencil pushingon paper; reaction: paper push-ing on pencil).

4. Newton’s first law states thatobjects at rest stay at rest andobjects in motion stay in motionunless acted on by an unbal-anced force.

5. Newton’s second law statesthat the acceleration of an objectincreases as the force acting onit increases but the accelerationdecreases as the mass of theobject increases.

6. F � 70 kg � 4.2 m/s2 � 294 N7. The action and reaction forces

do not balance each otherbecause the forces are acting ontwo different objects. Becausethey act on two different objects,you cannot combine them todetermine a net force.

8. Sample answer: During a head-on collision, an unbalanced forcestops the motion of the car. Butno unbalanced force immediatelyacts on the people inside the car.The people continue to moveforward. Airbags are importantbecause they provide unbal-anced forces to stop the motionof the people in the car. Theairbags prevent the people fromhitting the dashboard or wind-shield of the car.

9. Your hand hit the table witha certain amount of force.According to Newton’s third lawof motion, the table exerts anequal and opposite force on yourhand. The force exerted by thetable causes your hand to hurt.

CHAPTER RESOURCES


CRF • Section Quizg• Section Reviewg• Vocabulary and Section Summaryg• SciLinks Activityg• Datasheet for Quick Lab


READING STRATEGY

MomentumImagine a compact car and a large truck traveling with the same velocity. The drivers of both vehicles put on the brakes at the same time. Which vehicle will stop fi rst?

You would probably say that the compact car will stop first. Youknow that smaller objects are easier to stop than larger objects.But why? The answer is momentum (moh MEN tuhm).

Momentum, Mass, and VelocityThe momentummomentum of an object depends on the object’s mass andvelocity. The more momentum an object has, the harder it is tostop the object or change its direction. In the example above,the truck has more mass and more momentum than the car has.So, a larger force is needed to stop the truck. Similarly, a fast-moving car has a greater velocity and thus more momentumthan a slow-moving car of the same mass. So, a fast-movingcar is harder to stop than a slow-moving car. Figure 1 showsanother example of an object that has momentum.

Calculating MomentumMomentum (p) can be calculated with the equation below:

In this equation, m is the mass of an object in kilograms andv is the object’s velocity in meters per second. The units ofmomentum are kilograms multiplied by meters per second, orkg•m/s. Like velocity, momentum has a direction. Its directionis always the same as the direction of the object’s velocity.

3

momentummomentum a quantity defined as the product of the mass and velocity of an object

Figure 1 The teen on the right has less mass than the teen on the left. But, the teen on the right can have a large momentum by moving quickly when she kicks.

p � m � v

What You Will Learn

Calculate the momentum of movingobjects.Explain the law of conservation ofmomentum.

Vocabularymomentum

Prediction Guide Before readingthis section, write the title of eachheading in this section. Next, undereach heading, write what you thinkyou will learn.

OverviewIn this section, students learnabout momentum and performcalculations with the equationfor momentum. Students alsostudy the law of conservationof momentum and learn howit relates to Newton’s third lawof motion.

BellringerTell students that this sectionis about momentum. Then,ask students to make a listof five things that they thinkhave momentum and five thingsthat don’t have momentum.

GroupGroup vv -------g

Testing Momentum Give eachgroup of students two balls thathave different masses. Have stu-dents take turns rolling the ballsto each other with the samevelocity. Ask the students tocompare the forces needed tostop the balls. (More force isneeded to stop the ball with moremass.) Ask students to explainwhy different forces are needed.(The ball that has more mass hasmore momentum. Therefore, it isharder to stop.) l Kinesthetic

3

CHAPTER RESOURCES


CRF • Lesson Plan • Directed Reading Ab • Directed Reading Bs

Technology

Transparencies • Bellringer

Workbooks

Interactive Textbook Struggling Readers Struggling Readers

Math Skills for Science • Momentumg


The Law of Conservation of MomentumWhen a moving object hits another object, some or all of themomentum of the first object is transferred to the object thatis hit. If only some of the momentum is transferred, the restof the momentum stays with the first object.

Imagine that a cue ball hits a billiard ball so that the bil-liard ball starts moving and the cue ball stops, as shown inFigure 2. The white cue ball had a certain amount of momen-tum before the collision. During the collision, all of the cueball’s momentum was transferred to the red billiard ball. Afterthe collision, the billiard ball moved away with the sameamount of momentum the cue ball had. This example showsthe law of conservation of momentum. The law of conservationof momentum states that any time objects collide, the totalamount of momentum stays the same. The law of conservationof momentum is true for any collision if no other forces acton the colliding objects. This law applies whether the objectsstick together or bounce off each other after they collide.

✓Reading Check What can happen to momentum when twoobjects collide? (See the Appendix for answers to Reading Checks.)

Momentum Calculations What is the momen-tum of an ostrich with a mass of 120 kg thatruns with a velocity of 16 m/s north?

Step 1: Write the equation for momentum.

p � m � v

Step 2: Replace m and v with the values givenin the problem, and solve.

p � 120 kg � 16 m/s north

p � 19,200 kg•m/s north

Now It’s Your Turn1. What is the momentum of a 6 kg bowl-

ing ball that is moving at 10 m/s downthe alley toward the pins?

2. An 85 kg man is jogging with a velocityof 2.6 m/s to the north. Nearby, a 65 kgperson is skateboarding and is travelingwith a velocity of 3 m/s north. Whichperson has greater momentum? Showyour calculations.

Figure 2 The momentumbefore a collision is equalto the momentum afterthe collision.

Momentum

Momentum

Research -------------------------------------------aConservation of Momentum inTwo Dimensions In this sec-tion, the discussion of conserva-tion of momentum is limitedto head-on, one-dimensional(or straight-line) collisions.Momentum is also conservedin two and three dimensions,but, the calculations are morecomplex. Have students researchconservation of momentum intwo dimensions. Then, ask themto make a poster of real-life situ-ations in which momentum isconserved in two dimensions.l Logical/Visual


Momentum Vectors Themomentum arrows, or vectors, inFigure 2 do not represent forces.Momentum, like force, is a vectorquantity and can therefore beshown with arrows. However, thearrows in Figure 4 in this sectionare force vectors. l Visual


When two objects collide, some or all of themomentum of each object can be transferredto the other object.


1. p � 6 kg � 10 m/s down the alley �

60 kg•m/s down the alley2. The man jogging has greater momentum.

p � 85 kg � 2.6 m/s north �

221 kg•m/s north (man jogging)p � 65 kg � 3 m/s north �

195 kg•m/s north (person skateboarding)

SUPPORT FOR

English LanguageLearnersToy Car Momentum Studentswill better understand conser-vation of momentum with theaid of a demonstration. As younarrate the process, write keyterms on the board. Check tomake sure students understandthese terms before beginning.First, place one toy car in thecenter of a table. Then, roll anidentical car so that it hits thefirst car head on. The secondcar should stop moving, andthe first car should start mov-ing with a velocity equal tothe second car’s initial velocity.You can demonstrate differenttypes of collisions by changingthe initial velocity of one orboth cars. (Note: Momentumwill not be perfectly conservedbecause friction will act on thecars.)l Visual

Section 3 • Momentum 167

Objects Sticking TogetherSometimes, objects stick together after a collision. The footballplayers shown in Figure 3 are an example of such a collision.A dog leaping and catching a ball and a teen jumping on askateboard are also examples. After two objects stick together,they move as one object. The mass of the combined objectsis equal to the masses of the two objects added together. In ahead-on collision, the combined objects move in the directionof the object that had the greater momentum before the colli-sion. But together, the objects have a velocity that differs fromthe velocity of either object before the collision. The objectshave a different velocity because momentum is conserved anddepends on mass and velocity. So, when mass changes, thevelocity must change, too.

Objects Bouncing Off Each OtherIn some collisions, the objects bounce off each other. Thebowling ball and bowling pins shown in Figure 3 are examplesof objects that bounce off each other after they collide. Bil-liard balls and bumper cars are other examples. During thesetypes of collisions, momentum is usually transferred from oneobject to another object. The transfer of momentum causesthe objects to move in different directions at different speeds.However, the total momentum of all the objects will remainthe same before and after the collision.

✓Reading Check What are two ways that objects may interactafter a collision?

When football players tackle another player, they sticktogether. The velocity of each player changes after thecollision because of conservation of momentum.

Although the bowling ball and bowling pins bounceoff each other and move in different directions aftera collision, momentum is neither gained nor lost.

Momentumand Language

The word momentum is oftenused in everyday language. Forexample, a sports announcermay say that the momentumof a game has changed. Oryou may read that an ideais gaining momentum. Inyour science journal, writea paragraph that explainshow the everyday use of theword momentum differs frommomentum in science.

WRITINGSKILL

Examples of Conservation of MomentumFigure 3

Reteaching -------------------------------------bVelocity and Momentum Tellstudents that slow-moving objectsthat have large masses canhave more momentum thanfast-moving objects that havesmaller masses. For example, alarge cruise ship moving slowlyinto port has more momentumthan a person running very fast.Have students describe otherslow-moving objects that havea large momentum. l Verbal

Quiz ---------------------------------------------------------------------g

1. What is the equation formomentum? (p � m � v)

2. Give an example of an objectwith a small mass that has alarge momentum. Explainyour answer. (Sample answer:A fastball pitched by a baseballpitcher has a small mass but alarge velocity. Therefore, the ballhas a large momentum.)

AlternativeAssessment ---------------------------a

Writing Momentum AnalysisHave students choose asport that they partici-

pate in or that they can watch.Then, ask students to write aone-page paper describing howconservation of momentumaffects the movement of theplayers or the objects used inthe game. l Verbal


After a collision, objects can stick togetheror can bounce off each other.




SummarySummary

Review

Conservation of Momentum and Newton’s Third LawConservation of momentum can be explained by Newton’sthird law of motion. In the example of the billiard ball, thecue ball hit the billiard ball with a certain amount of force.This force was the action force. The reaction force was theequal but opposite force exerted by the billiard ball on the cueball. The action force made the billiard ball start moving, andthe reaction force made the cue ball stop moving, as shownin Figure 4. Because the action and reaction forces are equaland opposite, momentum is neither gained nor lost.

• Momentum is a propertyof moving objects.

• Momentum is calcu-lated by multiplying themass of an object by theobject’s velocity.

• When two or moreobjects collide, momen-tum may be transferred,but the total amountof momentum doesnot change. This is thelaw of conservation ofmomentum.

Using Key Terms

1. Use the following term in a sen-tence: momentum.


2. Which of the following has thesmallest amount of momentum?

a. a loaded truck driven at high-way speeds

b. a track athlete running a racec. a baby crawling on the floord. a jet airplane being towed

toward an airport

3. Explain the law of conservationof momentum.

4. How is Newton’s third law ofmotion related to the law ofconservation of momentum?

Math Skills

5. Calculate the momentum of a2.5 kg puppy that is runningwith a velocity of 4.8 m/s south.

Critical Thinking

6. Applying Concepts A car and atrain are traveling with the samevelocity. Do the two objectshave the same momentum?Explain your answer.

7. Analyzing Ideas When youcatch a softball, your hand andglove move in the same direc-tion that the ball is moving.Analyze the motion of yourhand and glove in terms ofmomentum.

Topic: MomentumSciLinks code: HSM0988

Figure 4 The action forcemakes the billiard ball beginmoving, and the reaction forcestops the cue ball’s motion.

Action force Reaction force


1. Sample answer: To calculatethe momentum of an object,multiply the mass of the objectby its velocity.

2. c3. The law of conservation of

momentum states that any timeobjects collide, the total amountof momentum stays the same. Thelaw of conservation of momen-tum is true when no other forcesact on the objects.

4. Newton’s third law can explainthe law of conservation ofmomentum. Because the actionand reaction forces are equaland opposite, momentum isneither gained nor lost.

5. p � 2.5 kg � 4.8 m/s south �

12 kg•m/s south6. No, although the train and the

car have the same velocity, thetrain has more mass than thecar, so the train has greatermomentum.

7. The softball has momentum as ittravels toward your glove. Whenthe ball hits your glove, some ofits momentum is transferred toyour glove and your hand. As aresult, your glove and hand movein the direction that the ball wasmoving before the catch.

CHAPTER RESOURCES


CRF • Section Quizg• Section Reviewg• Vocabulary and Section Summaryg• Critical Thinkinga

Section 3 • Momentum 169

LabSkills Practice

Observe several effects ofinertia.

Describe the motion ofobjects in terms of inertia.

Station 1

• egg, hard-boiled

• egg, rawStation 2

• card, index

• coin

• cupStation 3

• mass, hanging, 1 kg

• meterstick

• scissors

• thread, spool

Inertia-Rama!Inertia is a property of all matter, from small particles of dustto enormous planets and stars. In this lab, you will investigatethe inertia of various shapes and kinds of matter. Keep inmind that each investigation requires you to either overcomeor use the object’s inertia.

Station 1: Magic EggsProcedure

1 There are two eggs at this station—one is hard-boiled (solidall the way through) and the other is raw (liquid inside). Themasses of the two eggs are about the same. The eggs are notmarked. You should not be able to tell them apart by theirappearance. Without breaking them open, how can you tellwhich egg is raw and which egg is hard-boiled?

2 Before you do anything to either egg, make some predictions.Will there be any difference in the way the two eggs spin?Which egg will be the easier to stop?

3 First, spin one egg. Then, place your finger on it gently to makeit stop spinning. Record your observations.

4 Repeat step 3 with the second egg.

5 Compare your predictions with your observations. (Repeatsteps 3 and 4 if necessary.)

6 Which egg is hard-boiled and which one is raw? Explain.

Analyze the Results

1 Explaining Events Explain why the eggs behave differentlywhen you spin them even though they should have the sameinertia. (Hint: Think about what happens to the liquid insidethe raw egg.)

Draw Conclusions

2 Drawing Conclusions Explain why the eggs react differentlywhen you try to stop them.

OBJECTIVES

SAFETY

MATERIALS

?

Skills PracticeSkills Practice LabLab

Inertia-Rama!

Teacher’s Notes

Time RequiredTwo 45-minute class periods

Lab Ratings

rTeacher Prep ff

Student Set-Up f

Concept Level ff

Clean Up f

M A T E R I A L S1. Be sure to have a few extra raw

and hard-boiled eggs on hand.Having students spin their eggs ina box may reduce the chancethat an egg will break.

2. Use a relatively large coin, suchas a quarter or 50-cent piece. Oryou may have students try theStation 2 procedure with coinsof different sizes and comparethe results.

3. The mass used at Station 3should be at least 1 kg. A largermass will give better results.

Safety CautionRemind students to review allsafety cautions and icons beforebeginning this lab activity.

Preparation NotesThis lab may be done in oneclass period if enough suppliesare available to avoid changingstations.

CHAPTER RESOURCES


CRF • Datasheet for Chapter Lab• Lab Notes and Answers

Technology

Classroom Videos• Lab Video

• A Marshmallow Catapult• Blast Off!• Quite a Reaction

Vicky Farland

Crane Junior HighYuma, Arizona

Holt Lab Generator CD-ROMSearch for any lab by topic, standard, difficulty level,or time. Edit any lab to fit your needs, or create yourown labs. Use the Lab Materials QuickList softwareto customize your lab materials list.

CLASSROOM

TESTED& APPRO

VED


Station 2: Coin in a CupProcedure

1 At this station, you will find a coin, an indexcard, and a cup. Place the card over the cup.Then, place the coin on the card over the cen-ter of the cup, as shown below.

2 Write down a method for getting the coin intothe cup without touching the coin and withoutlifting the card.

3 Try your method. If it doesn’t work, try againuntil you find a method that does work.

Analyze the Results

1 Describing Events Use Newton’s first law ofmotion to explain why the coin falls into thecup if you remove the card quickly.

Draw Conclusions

2 Defending Conclusions Explain why pullingon the card slowly will not work even thoughthe coin has inertia. (Hint: Friction is a force.)

Station 3:The Magic ThreadProcedure

1 At this station, you will find aspool of thread and a mass hang-ing from a strong string. Cut apiece of thread about 40 cm long.Tie the thread around the bottomof the mass, as shown at right.

2 Pull gently on the end of thethread. Observe what happens,and record your observations.

3 Stop the mass from moving. Nowhold the end of the thread so thatthere is a lot of slack betweenyour fingers and the mass.

4 Give the thread a quick, hard pull.You should observe a very differ-ent event. Record your observa-tions. Throw away the thread.

Analyze the Results

1 Analyzing Results Use Newton’s first law ofmotion to explain why the result of a gentlepull is different from the result of a hard pull.

Draw Conclusions

2 Applying Conclusions Both moving and non-moving objects have inertia. Explain why throw-ing a bowling ball and catching a thrownbowling ball are hard.

3 Drawing Conclusions Why is it harder to runwith a backpack full of books than to run withan empty backpack?

Station 2Analyze the Results

1. The coin remains at rest,so when the card is removedquickly, there is not enough fric-tion to move the coin. So, thecoin falls into the cup when thecard is removed.

Draw Conclusions

2. When you pull slowly, thereis enough time for the frictionbetween the card and the cointo move the coin. So, the coinremains on the card.


1. The mass tends to stay at rest.A gentle pull exerts a smallforce over a longer time andmoves the mass, but a hardpull breaks the thread beforethe mass moves.

Draw Conclusions

2. It is just as hard to catch thebowling ball as it is to throw thebowling ball because the bowl-ing ball has the same inertia inboth cases.

3. Accept all reasonable answersthat take into account the addedinertia of the objects in thebackpack. Sample answer:Starting and stopping will beharder because the extra massincreases your inertia. In addi-tion, the books in the backpackact as the liquid inside a rawegg does. As you bounce up,they resist your upward move-ment. As you bounce down, theyare still moving upward.

CHAPTER RESOURCESWorkbooks

Whiz-Bang Demonstrations• Newton’s Eggciting Experimentb• Inertia Can Hurt Yag• Fountain of Knowledgeb

Inquiry Labs• On the Fast Tracka

Long-Term Projects & Research Ideas• “Any Color You Want, so Long as It’s

Black”a

Calculator-Based Labs• Falling Objectsa• Graphing Your Motiona


1. The liquid inside the raw egg sloshes,it doesn’t spin smoothly as thehard-boiled egg does.

Draw Conclusions

2. When you stop the eggs, the hard-boiledegg stops as a whole, while the shell ofthe raw egg can be stopped and the liquidinside keeps spinning.

Chapter 6 • Chapter Lab 171

Complete each of the following sen-tences by choosing the correct term from the word bank.

free fall projectile motioninertia terminal velocity momentum

1 An object in motion has , so it tends to stay in motion.

2 An object is falling at its if it falls at a constant velocity.

3 is the path that a thrown object follows.

4 is a property of moving objects that depends on mass and velocity.

5 occurs only when air resistance does not affect the motion of a falling object.

Multiple Choice

6 When a soccer ball is kicked, the action and reaction forces do not can-cel each other out because

a. the forces are not equal in size.b. the forces act on different objects.c. the forces act at different times.d. All of the above

7 An object is in projectile motion if it

a. is thrown with a horizontal push.b. is accelerated downward by gravity.c. does not accelerate horizontally.d. All of the above

8 Newton’s fi rst law of motion applies to

a. moving objects.b. objects that are not moving.c. objects that are accelerating.d. Both (a) and (b)

9 To accelerate two objects at the same rate, the force used to push the object that has more mass should be

a. smaller than the force used to push the object that has less mass.

b. larger than the force used to push the object that has less mass.

c. the same as the force used to push the object that has less mass.

d. equal to the object’s weight.

0 A golf ball and a bowling ball are mov-ing at the same velocity. Which of the two has more momentum?

a. The golf ball has more momentum because it has less mass.

b. The bowling ball has more momen-tum because it has more mass.

c. They have the same momentum because they have the same velocity.

d. There is not enough information to determine the answer.

USING KEY TERMS

UNDERSTANDING KEY IDEAS


ANSWERS

Using Key Terms1. inertia2. terminal velocity3. Projectile motion4. Momentum5. Free fall

Understanding Key Ideas6. b7. d8. d9. b

10. b

Assignment GuideSECTION QUESTIONS

1 2–3, 5, 7, 11–12, 15

2 1, 6, 8–9, 13, 16, 18

3 4, 10, 17, 19

1 and 3 14

Short Answer

q Give an example of an object that is infree fall.

w Describe how gravity and air resistanceare related to an object’s terminalvelocity.

e Why can friction make observingNewton’s fi rst law of motion diffi cult?

Math Skills

r A 12 kg rock falls from rest off a cliffand hits the ground in 1.5 s.

a. Without considering air resistance,what is the rock’s velocity just beforeit hits the ground?

b. What is the rock’s momentum justbefore it hits the ground?

tConcept Mapping Use the followingterms to create a concept map: gravity,free fall, terminal velocity, projectilemotion, and air resistance.

y Identifying Relationships During aspace shuttle launch, about 830,000 kgof fuel is burned in 8 min. The fuelprovides the shuttle with a constantthrust, or forward force. How doesNewton’s second law of motionexplain why the shuttle’s accelerationincreases as the fuel is burned?

uAnalyzing Processes When using ahammer to drive a nail into wood, youhave to swing the hammer throughthe air with a certain velocity. Becausethe hammer has both mass and veloc-ity, it has momentum. Describe whathappens to the hammer’s momentumafter the hammer hits the nail.

iApplying Concepts Suppose you arestanding on a skateboard or on in-lineskates and you toss a backpack fullof heavy books toward your friend.What do you think will happen toyou? Explain your answer in terms ofNewton’s third law of motion.

o The picture below shows a commondesk toy. If you pull one ball up andrelease it, it hits the balls at the bot-tom and comes to a stop. In the sameinstant, the ball on the other sideswings up and repeats the cycle. Howdoes conservation of momentumexplain how this toy works?

CRITICAL THINKING

INTERPRETING GRAPHICS

CHAPTER RESOURCES


CRF • Chapter Reviewg• Chapter Test Ag• Chapter Test Ba• Chapter Test Cs• Vocabulary Activityg

Workbooks

Study Guide• Study Guide is also available in Spanish.

11. Accept all reasonable answers. Sampleanswers: A feather falling inside a vacuumchamber is in free fall. An object droppedon the moon is in free fall.

12. Gravity and air resistance combine to givea net force on a falling object. When gravityand air resistance are the same size but inopposite directions, the object stops accel-erating downward and has reached itsterminal velocity.

13. Friction is a force that opposes the motionof objects. Friction slows the motion ofmoving objects so you don’t see objectsmoving forever in a straight line.

14. a. �v � g � t � 9.8 m/s2 �

1.5 s � 14.7 m/sb. p � m � v � 12 kg �

14.7 m/s � 176.4 kg•m/s

Critical Thinking15. An answer to this

exercise can befound at the endof this book.

16. Newton’s second law:a � F � m. During takeoff, theshuttle burns fuel and thereforeloses mass. However, theforward force on the shuttleremains the same. So, theshuttle’s acceleration increasesbecause its mass constantlydecreases during takeoff.

17. When the hammer hits thenail, the hammer stops. Itsmomentum is transferred to thenail, driving it into the wood.Momentum is also transferredfrom the hammer to your handand from the nail to the woodand to the work bench ortable top.

18. You will move away from yourfriend (in the direction oppositefrom where you threw thebackpack). The action forceis you pushing the backpacktoward your friend. The reac-tion force is the backpackpushing you away from yourfriend.

Interpreting Graphics19. The law of conservation

of momentum: when two ormore objects interact, the totalamount of momentum must staythe same. The ball moving inthe air has a certain amount ofmomentum, and the balls at resthave no momentum. When themoving ball hits the balls atrest, all of its momentum istransferred to them, and itcomes to a stop. The momen-tum is transferred from ball toball until it reaches the ball onthe other end. The ball on theother end keeps all the momen-tum, and it moves away fromthe other balls.

Chapter 6 • Chapter Review 173

READINGRead each of the passages below. Then, answer the questions that follow each passage.

Passage 1 How do astronauts prepare for trips in the space shuttle? One method is to use simula-tions on Earth that mimic the conditions in space. For example, underwater training lets astronauts experience reduced gravity. They can also ride on NASA’s modified KC-135 airplane. NASA’s KC-135 simulates how it feels to be in a space shuttle. How does this airplane work? It flies upward at a steep angle and then flies downward at a 45° angle. When the airplane flies downward, the effect of reduced gravity is produced. As the plane falls, the astronauts inside the plane can float like astronauts in the space shuttle do!

1. What is the purpose of this passage?

A to explain how astronauts prepare for missions in space

B to convince people to become astronautsC to show that space is similar to EarthD to describe what it feels like to fl oat in space

2. What can you conclude about NASA’s KC-135 from the passage?

F NASA’s KC-135 is just like other airplanes.G All astronauts train in NASA’s KC-135.H NASA’s KC-135 simulates the space shuttle

by reducing the effects of gravity.I Being in NASA’s KC-135 is not very much

like being in the space shuttle.

3. Based on the passage, which of the following statements is a fact?

A Astronauts always have to train underwater.B Flying in airplanes is similar to riding in the

space shuttle.C People in NASA’s KC-135 fl oat at all times.D Astronauts use simulations to learn what

reduced gravity is like.

Passage 2 There once was a game that could be played by as few as 5 or as many as 1,000 players. The game could be played on a small field for a few hours or on a huge tract of land for several days. The game was not just for fun—in fact, it was often used as a substitute for war. One of the few rules was that the players couldn’t touch the ball with their hands—they had to use a special stick with webbing on one end. Would you believe that this game is the same as the game of lacrosse that is played today?

Lacrosse is a game that was originally played by Native Americans. They called the game baggataway, which means “little brother of war.” Although lacrosse has changed and is now played all over the world, it still requires special, webbed sticks.

1. What is the purpose of this passage?

A to explain the importance of rules in lacrosse

B to explain why sticks are used in lacrosseC to describe the history of lacrosseD to describe the rules of lacrosse

2. Based on the passage, what does the word substitute mean?

F something that occurs before warG something that is needed to play lacrosseH something that is of Native American originI something that takes the place of

something else


Answers to the standardized test preparation can help you identify student misconcep-tions and misunderstandings.

Teacher’s NoteTeacher’s NoteTo provide practice under more realistic testing conditions, give students 20 minutes to answer all of the questions in this Standardized Test Preparation.

Passage 21. C2. I Question 1: Although some of the rules of

lacrosse are mentioned in the passage, the main purpose of the article is not to explain the impor-tance of lacrosse rules or to describe lacrosse rules. Instead, the passage focuses on how and why the game that is now known as lacrosse was originally played. Therefore, the purpose of the passage is to describe the history of lacrosse.

Passage 11. A2. H3. D

Question 3: Some students may pick answer choice A because the passage states that astronauts train underwater. However, the passage also states that astronauts train in a modified KC-135 airplane. Students should recognize that the training on this airplane is not done underwater, so the statement that astronauts always have to train underwater is incorrect.

READING

MISCONCEPTIONALERT

Stand

ardized

Test Prep

aration

6

7

1. Which of the following images shows an object with no momentum that is about to be set in motion by an unbalanced force?

A

B

C

D

2. During a laboratory experiment, liquid was collected in a graduated cylinder. What is the volume of the liquid?

F 30 mLG 35 mLH 40 mLI 45 mL

Read each question below, and choose the best answer.

Read each question below, and choose the best answer.

1. The table below shows the accelerations produced by different forces for a 5 kg mass. Assuming that the pattern continues, use this data to predict what acceleration would be produced by a 100 N force.

A 10 m/s2

B 20 m/s2

C 30 m/s2

D 100 m/s2

2. The average radius of the moon is 1.74 � 106 m. What is another way to express the radius of the moon?

F 0.00000174 mG 0.000174 mH 174,000 mI 1,740,000 m

3. The half price bookstore is selling 4 paperback books for a total of $5.75. What would the price of 20 paperback books be?

A $23.00B $24.75C $28.75D $51.75

4. A 75 kg speed skater is moving with a velocity of 16 m/s east. What is the speed skater’s momentum? (Momentum is calculated with the equation: momentum � mass � velocity.)

F 91 kg•m/sG 91 kg•m/s eastH 1,200 kg•m/s eastI 1,200 kg•m/s2 east

INTERPRETING GRAPHICS MATH

Force Acceleration

25 N 5 m/s2

50 N 10 m/s2

75 N 15 m/s2

Chapter 6 • Standardized Test Preparation 175

INTERPRETING GRAPHICS1. B2. G

Question 1: To answer this ques-tion, students must remember that momentum is equal to the product of mass and velocity. Because all objects have mass, the only way an object can have no momentum is if its veloc-ity is 0 m/s. Only answer choices B and D have objects with no momen-tum. However, answer choice D does not show any impending unbalanced force. Answer choice B shows that the cue stick is moving and is about to exert an unbalanced force on the cue ball (that has no momentum). Therefore, B is the correct answer.

MATH1. B2. I3. C4. H

Question 4: The product of 75 and 16 is 1,200. Some students may have difficulty selecting between answer choices H and I because both choices appear to have the correct answer. However, answer choice I has units of kilograms-meters per second squared (kg•m/s2) and the correct units for momentum are kilograms-meters per second (kg•m/s). Answer choice H is correct.

CHAPTER RESOURCES


CRF • Standardized Test Preparation g

State Resources

For specifi c resources for your state, visit go.hrw.com and type in the keyword HSMSTR.

in Action

in Action

Language ArtsImagine that you were in London on June 10, 2000 and walked across the

Millennium Bridge. Write a one-page story about what you think it was like on the bridge that day.

MathThe pound (symbol £) is the currency in England. The inventor of the suit thinks that it will be sold for £1200. How much will the suit cost in dollars if $1 is equal to £0.60?

WRITINGSKILL

Scientific DiscoveriesThe Millennium BridgeYou may have heard the children’s song, “London Bridge is falling down . . .”. Lon-don Bridge never fell. But some people who walked on the Millennium Bridge thought that it might fall instead! The Millennium Bridge is a pedestrian bridge in London, Eng-land. The bridge opened on June 10, 2000, and more than 80,000 people crossed it that day. Immediately, people noticed something wrong—the bridge was swaying! The bridge was closed after two days so that engineers could determine what was wrong. After much research, the engineers learned that the force of the footsteps of the people cross-ing the bridge caused the bridge to sway.

Science, Technology,

and SocietyPower Suit for Lifting PatientsImagine visiting a hospital and seeing someone who looked half human and half robot. No, it isn’t a scene from a science fic-tion movie—it is a new invention that may some day help nurses lift patients easily. The invention, called a power suit, is a metal framework that a nurse would wear on his or her back. The suit calculates how much force a nurse needs to lift a patient, and then the robotic joints on the suit help the nurse exert the right amount of force. The suit will also help nurses avoid injuring their backs.


Scientific Discoveries

BackgroundThe Millennium Bridge swayed because the people walking on the bridge subconsciously started to walk in-step. The steps of the people matched the reso-nant frequency of the bridge, which caused the bridge to sway even more. This phenomenon has been observed on a few other bridges. In fact, march-ing soldiers are often instructed to “break step” when crossing bridges to avoid the possibility of marching at the bridge’s reso-nant frequency.

The engineers who built the Millennium Bridge installed dampers and shock absorbers to stop the swaying of the bridge. The bridge reopened on February 22, 2003.

Science, Technology,

and Society

Discussion ---------------------------------- GENERAL

Lead a discussion about the ben-efits of the power suit. (Sampleanswers: The power suit will make nurses’ jobs easier. The power suit will prevent back injuries.) Ask students to describe other situa-tions or jobs that may benefit from the use of the power suit. (Sample answer: Construction workers and people who move furniture could benefit from the power suit.)

Answer to Language Arts Activity

Accept all reasonable answers. Students may describe the motion of the bridge or how they felt when the bridge started to sway. Students may also describe the reaction of the other people on the bridge.

Answer to Math Activity

£1200 � $1 � £0.60 � $2,000The answer to this Math Activity may vary as the rate of exchange between the dollar and the pound changes. As an extension, you may ask your students to research the current exchange rate and find the current price of the power suit.

Social Studies

Research the history of roller coasters to learn how roller coaster design has changed over time. Make a poster to sum-marize your research.

To learn more about these Science in Action topics, visitgo.hrw.com and type in thekeyword HP5FORF.

Check out Current Science®

articles related to this chapter by visiting go.hrw.com. Just type in the keyword HP5CS06.

Steve OkamotoRoller Coaster Designer Roller coasters have fascinated Steve Okamoto ever since his first ride on one. “I remember going to Disneyland as a kid. My mother was always upset with me because I kept looking over the sides of the rides, trying to fig-ure out how they worked,” he says. To satisfy his curiosity, Okamoto became a mechanical engineer. Today he uses his scientific knowledge to design and build machines, systems, and buildings. But his specialty is roller coasters.

Roller coasters really do coast along the track. A motor pulls the cars up a high hill to start the ride. After that, the cars are powered by only gravity. Designing a successful roller coaster is not a simple task. Okamoto has to cal-culate the cars’ speed and acceleration on each part of the track. He must also consider the safety of the ride and the strength of the structure that supports the track.

Chapter 6 • Science in Action 177

Careers

BackgroundSteve Okamoto has a degree in product design. He studied both mechanical engineering and stu-dio art. Product designers con-sider an object’s form as well as its function and take into account the interests and abili-ties of the product’s consumer.

Two of Okamoto’s first coasters were the Ninjas at Six Flags Over Mid-America, in St. Louis, Missouri, and Six Flags Magic Mountain, in Los Angeles, California.

When designing a ride, Okamoto studies site maps of the location, then goes to the amusement park to look at the actual site. Because most rides he designs are for older parks, fitting a coaster around, above, and between existing rides and buildings is one of his biggest challenges. Most rides and parks also have some kind of theme, so marketing goals and con-cerns figure into his designs as well. (As an example, Okamoto designed a roller coaster named the Mamba. The coaster is named for one of the fastest snakes in Africa and is designed around this theme.)

Answer to Social Studies Activity

Accept all reasonable answers. Student posters may show different types of roller coasters including old-fashioned wooden roller coasters and modern steel-tube roller coasters. You may wish to challenge students to learn when the first roller coaster was built or to learn when the first roller coaster with a loop was built.

6 forces and motion compression guide: chapter planning guide · section 2 newton’s laws of...

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