Work, Machines, and Energy - · PDF fileUNIT TIMELINE 3 Work, Machines, and Energy Can you imagine living in a world with no machines? In this unit, you will explore the scientific

UNIT

T I M E L I N E

3

Work, Machines, and EnergyCan you imagine living in a world with no machines? In this unit, you will explore the scientific meaning of work and learn how machines make work easier. You will find out how energy allows you to do work and how different forms of energy can be converted into other forms of energy. You will also learn about heat and how heating and cooling systems work. This timeline shows some of the inventions and discoveries made throughout history as people have advanced their understand-ing of work, machines, and energy.

206 Unit 3

Around3000 BCE

The sail is used in

Egypt. Sails use the

wind rather than

human power to

move boats through

the water.

German inventor Baron

Karl von Drais de

Sauerbrun exhibits the

first two-wheeled, rider-

propelled machine.

Made of wood,

this early machine

paves the way for

the invention of

the bicycle.

1972The first American

self-service gas

station opens.

1948Maria Telkes, a Hungarian-born

physicist, designs the heating

system for the first solar-heated

house.

1818

Work, Machines, and Energy 207

1893The “Clasp

Locker,“ an

early zipper,

is patented.

Around200 BCE

Under the Han dynasty,

the Chinese become one

of the first civilizations to

use coal as fuel.

1656Dutch scientist

Christiaan Huygens

invents the

pendulum clock.

1776The American

colonies declare

their independence

from Great Britain.

1908The automobile age begins

with the mass production of

the Ford Model T.

1926American scientist Robert

Goddard launches the first

rocket powered by liquid

fuel. The rocket reaches

a height of 12.5 m and a

speed of 97 km/h.

A wind-powered generator

begins generating electrical

energy in Scotland’s Orkney

Islands.

1988A two-wheeled, battery-

powered “people mover”

is introduced. Gyroscopes

and tilt sensors allow

riders to guide the

scooter-like transporter

by leaning.

2001The 2000 Olympic

Summer Games are

held in Sydney, Australia.

2000

OBJECTIVES LABS, DEMONSTRATIONS, AND ACTIVITIES TECHNOLOGY RESOURCES

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

8 Work and MachinesChapter Planning Guide

Chapter Opener

207A Chapter 8 • Work and Machines

OSP Lesson Plans (also in print) TR Bellringer Transparency* TR P29 Work or Not Work?* TR P30 Force Times Distance* TR LINK TOLINK TO LIFE SCIENCELIFE SCIENCE L80 A Pair of

Muscles in the Arm*CRF SciLinks Activity*gVID Lab Videos for Physical ScienceCD Science Tutor

TE Activity Work in Sports, p. 210g TE Activity Work Done on a Spring Scale, p. 212g SE Quick Lab Get to Work!, p. 213 ◆g

CRF Datasheet for Quick Lab* SE Skills Practice Lab A Powerful Workout, p. 230g

CRF Datasheet for Chapter Lab* LB Inquiry Labs Get an Arm and an Egg Up*a SE Science in Action Math, Social Studies, and Language

Arts Activities, pp. 236–237g

Section 1 Work and Power• Determine when work is being done on an object.• Calculate the amount of work done on an object.• Explain the difference between work and power.

OSP Lesson Plans (also in print) TR Bellringer Transparency* TR P30 Input Force and Distance* TR P31 Machines Change the Size and/or

Direction of a Force* SE Internet Activity, p. 218gCD Science Tutor

TE Connection Activity Home Economics, p. 216g TE Activity Machines as Solutions to Problems,

p. 218a TE Connection Activity Math, p. 218g TE Connection Activity Life Science, p. 219g TE Connection Activity History, p. 219g SE School-to-Home Activity Useful Friction, p. 220g LB Whiz-Bang Demonstrations Pull-Ease, Please!*b LB Whiz-Bang Demonstrations A Clever Lever*b

PACING • 45 min pp. 216–221Section 2 What Is a Machine?• Explain how a machine makes work easier.• Describe and give examples of the force-distance

trade-off that occurs when a machine is used.• Calculate mechanical advantage.• Explain why machines are not 100% efficient.

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

TE Activity Loads on a First-Class Level, p. 222g TE Activity Classifying Tools, p. 223g TE Connection Activity Real World, p. 224g TE Activity Wheels and Axles, p. 225b TE Activity Gears, p. 225a TE Activity Zippers, p. 227g TE Activity Screws, p. 227b TE Connection Activity Math, p. 227g SE School-to-Home Activity Everyday Machines,

p. 228g SE Skills Practice Lab Inclined to Move, p. 719g SE Skills Practice Lab Wheeling and Dealing,

p. 720a SE Inquiry Lab Building Machines, p. 722b LB Long-Term Projects & Research Ideas To Complicate

Things*aCRF Datasheet for LabBook*

PACING • 45 min pp. 222–229Section 3 Types of Machines• Identify and give examples of the six types of simple

machines.• Analyze the mechanical advantage provided by each

simple machine.• Identify the simple machines that make up a

compound machine.

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. 209gpp. 208–215PACING • 135 min

CRF Vocabulary Activity*g SE Chapter Review, pp. 232–233g

CRF Chapter Review* ■g

CRF Chapter Tests A* ■g, B*a, C*s SE Standardized Test Preparation, pp. 234–235g

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 8 • Chapter Planning Guide 207B

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. 210g TE Reading Strategy Prediction Guide, p. 211g TE Support for English Language Learners, p. 211 TE Inclusion Strategies, p. 212 SE Math Focus More Power to You, p. 214g MS Math Skills for Science Work and Power*g

SE Reading Checks, pp. 210, 213, 214g TE Reteaching, p. 214b TE Quiz, p. 214g TE Alternative Assessment, p. 214g SE Section Review,* p. 215 ■g

CRF Section Quiz* ■g

UCP 3; SAI 1, 2; PS 3a; ChapterLab: SAI 1, 2; PS 3a; ST 2



SE Reading Strategy Prediction Guide, p. 216g TE Reading Strategy Concept Mapping, p. 217b SE Math Practice Finding the Advantage, p. 219g TE Support for English Language Learners, p. 219 MS Math Skills for Science Mechanical Advantage*g

SE Reading Checks, pp. 217, 218, 220g TE Homework, p. 218g TE Reteaching, p. 220b TE Quiz, p. 220g TE Alternative Assessment, p. 220g SE Section Review,* p. 221 ■g

CRF Section Quiz* ■g

UCP 3; SAI 1, 2; ST 2



SE Reading Strategy Mnemonics, p. 222g SE Math Focus Mechanical Advantage of an Inclined Plane,

p. 226g TE Support for English Language Learners, p. 226

CRF Reinforcement Worksheet Finding Machines in Everyday Life*bCRF Reinforcement Worksheet Mechanical Advantage and

Efficiency*bCRF Critical Thinking Building Works of Art*a

SE Reading Checks, pp. 223, 225, 226, 228g TE Reteaching, p. 228b TE Quiz, p. 228g TE Alternative Assessment, p. 228g SE Section Review,* p. 229 ■ g

CRF Section Quiz* ■ g

UCP 3, 5; SAI 1; ST 1, 2;LabBook: SAI 1

SE Pre-Reading Activity, p. 208gOSP Science Puzzlers, Twisters & Teasersg

National ScienceEducation Standards

SAI 1

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 HP5CS08T.

• 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 Resources

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 theresources shown here and thefollowing time-saving tools:

• Lab Materials QuickListSoftware

• Customizable lesson plans

• Holt Calendar Planner

•The powerfulExamView® TestGenerator

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 ?

207C Chapter 8 • Work and Machines

8

TEACHING TRANSPARENCIESBELLRINGER

TRANSPARENCIESCHAPTER STARTER

TRANSPARENCY

Would YouBelieve . . . ?

The Great Pyramid was built over4,000 years ago and remains oneof the Seven Wonders of the World.

The Great Pyramid, located in Giza(GEE zuh), Egypt, could be called thelargest tombstone ever created. A mon-ument and tomb for the pharaoh KingKhufu (KOO foo), it covers an area thesize of seven city blocks and rises about40 stories high. The Great Pyramid isthe largest of the three pyramids ofGiza. It was built around 2600 BCE andtook less than 30 years to complete—arelatively short period of time consid-ering that construction equipment didn’texist 4,000 years ago. So how did theEgyptians do it?

To build the Great Pyramid, theEgyptians cut and moved more than 2million stone blocks, most averaging2,000 kg (probably over 40 times yourown mass). The blocks were cut from astone quarry, moved near the pyramid,and then lifted into place. To finish inless than 30 years, the Egyptians would

have had to cut, move, and lift about200 blocks per day! The Egyptians didnot have cranes, bulldozers, or any otherheavy-duty machines. What they hadwere two simple machines—the inclinedplane and the lever.

Archaeologists have found theremains of inclined planes, or ramps,made from mud, stone, and wood. TheEgyptians pushed or pulled the blocksalong these ramps to raise them to theproper height. Using ramps required lessforce than lifting the blocks straight up.In addition, notches in many blocks indi-cate that huge levers were used like giantcrowbars to lift and move the heavyblocks. The workers pushed down on thelever, and the lever pushed up on a stoneblock, lifting it into place.

The Egyptians used simple machinesto create something truly amazing. In thischapter, you’ll learn about work and howmachines can help make work easier.

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

Work and Machines CHAPTER STARTER Work and Machines BELLRINGER TRANSPARENCY


Section: Work and PowerFirst, in your science journal, define what specifickind of work is being done in each activity below.Then, select the activities that require the leastamount of work.• carrying heavy books home• reading a 300-page novel• skiing for 1 hour• lifting a 45 kg mass• holding a steel beam in place for 3 hours• jacking up a car

Section: What Is a Machine?Write a one-paragraph answer in your science

journal to the following question:Why do we use machines?

Work or Not Work?TEACHING TRANSPARENCY


Yes

No

Yes

No

Wo

Example Directionof force

Directionof motion

Doing work?

P29 Force Times DistanceTEACHING TRANSPARENCY


The force needed to lift anobject is equal to the gravita-tional force on the object—inother words, the object’s weight.

W � 80 N � 1 m � 80 J

If you increase the weight, anincreased force is needed tolift the object. This increasesthe amount of work done.

W � 160 N � 1 m � 160 J W � 80 N � 2 m � 160 J

80 N

80 N

160 N

Increasing the distance alsoincreases the amount ofwork done.

P30

Input Force and Distance

W = 450 N × 1 m = 450 J W = 150 N × 3 m = 450 J

Lifting this box straight up requires aninput force equal to the weight of the box.

Using a ramp to lift the box requires an input force less thanthe weight of the box, but the input force must be exertedover a greater distance than if you didn’t use a ramp.

CONCEPT MAPPINGTRANSPARENCY

force

workoutput

applied through a which is which is

and is madeeasier by

machines,such as a

divided by divided by

is defined asis done by machines,

which have

Work and Machines CONCEPT MAPPING TRANSPARENCY


Use the following terms to complete the concept map below:work input, output force, work, lever, distance, input force,mechanical efficiency, mechanical advantage

TEACHING TRANSPARENCIES


TEACH

ING

TRA

NSPA

REN

CY

Machines Change the Size and/or Direction of a Force

A sim

ple pulleychanges thedirection

of theinput force, but thesize of the outputforce is the sam

e asthe input force.

A ham

mer

decreasesthe

force, but appliesit over a

greaterdistance.

When a screw

-driver is usedas a lever,it

increasesthe force anddecreases

thedistance overw

hich the forceis applied.

A nutcracker

increasesthe force butapplies it overa

shorterdistance.

orce

Ou

tpu

tfo

rce

Inp

ut

force

Inp

ut fo

rce

Ou

tpu

tfo

rce

Inp

ut

force

Ou

tpu

tfo

rceIn

pu

tfo

rce

Ou

tpu

tfo

rce

P31

A Pair of Muscles in the Arm


TEACH

ING

TRA

NSPA

REN

CY

Skeletal muscles, such as the biceps and triceps m

uscles, work

in pairs. When the biceps m

uscle contracts, the arm bends.

When the triceps m

uscle contracts, the arm straightens.

Biceps

muscle

Tricepsm

uscle

FlexorExten

sor

L80

Chapter: Body Organization and Structure

SAMPLE SAMPLE SAMPLE

Meeting Individual Needs

Review and Assessments

Labs and Activities

DIRECTED READING A VOCABULARY ACTIVITY REINFORCEMENT

STANDARDIZED TEST PREPARATIONCHAPTER 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

WHIZ-BANGDEMONSTRATIONS


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 new substances: 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 one location to another: ROOSINE

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

LONG-TERM PROJECTS & RESEARCH IDEAS INQUIRY LABS

STUDENT WORKSHEET

LAB

19

Name Date Class

Get an Arm and an Egg UpThe Happy Farm Egg Company has grown from a 20-chicken henhouse to a1,500-chicken corporation in only three years. The increased business is great,but the factory equipment, acquired from an old canning plant, was not built tohandle the fragile eggs. Each day, more than 200 eggs are broken as they aremoved to different parts of the factory for cleaning, sorting, grading, and pack-aging. Losing 1 egg is no big deal, but losing 200 eggs every day creates a highcost for this new company. The costs are mounting.

The owner of Happy Farms, Shelly Kluq, has decided to invest in a new typeof hydraulic technology. This system consists of a series of hydraulic arms thatlift eggs from the gatherers to the pickup window, across to the sorting and grad-ing section, and down to the packaging area.

As a hydraulics designer, you have been asked to provide Happy Farms with aworking model. However, you are competing against several other hydraulics de-signers. The designer with the most effective model will be awarded the contractto build the full-scale hydraulic system. You have one week to turn Happy Farms’scrambled system into an over-easy operation. Good luck!

Ask a QuestionHow do you build a hydraulic system for movingan egg upward, to the left, and then down?

Conduct an ExperimentJoin with 2 or 3 other students to discuss how you might solvethe problem. Hydraulic arms are moved by actuators, devicesthat use the pressure of a liquid to move or control an object.

1. Cut a 2.5 cm length of plastic tubing. Carefully thread thestem of the balloon through the plastic tubing.

2. From inside the tennis-ball can, carefully thread the tubingand balloon stem out through the hole of the can, as shownbelow. Secure the tubing in place with tape.

3. Repeat steps 1–2 with the second tennis-ball can.

4. Inflate both balloons to about half their capacity. For eachballoon, hold the balloon closed while inserting one end ofthe rest of the tubing into the balloon. Seal each connectionwith a twist tie. For a tight seal, wrap the tie at least twicearound the balloonstem. You have con-structed an actuator.

MATERIALS FOR THEACTUATOR

• 90 cm of flexible plas-tic tubing

• metric ruler• scissors• 2 small, round bal-

loons• 2 empty tennis-ball

cans (no lids)• masking tape• 2 metal twist ties• 12 oz aluminum

cans (4)

USEFUL TERMS

hydraulicoperated by the pres-sure created when fluidis forced through a tube

actuatora device that uses thepressure of a fluid tomove or control an object

Inputactuator

Outputactuator

Metal twist tie

DATASHEETS FOR QUICKLABS

DATASHEETS FOR QUICK LABS

VOCABULARY AND SECTION 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 Thinking Skills 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 by a. 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 sediment a . 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 break a. in the surf. c. in the open ocean.b. in the breaker zone. d. as their wavelength increases.

______ 6. Most ocean waves are formed by a . 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 is a. waxing. c. in the new moon phase.b. waning. d. in the full moon phase.

______10. The Milky Way is thought to be a. 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 means A 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

Chapter 8 • Chapter Resources 207D

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®.

Parallel Puzzle1. What do all the words in the left column have in common that is

not shared by any of the words in the right column?

ramp hammer

screw faucet

chisel axle

doorstop hinge

Wheel Puzzle2. The wheels of this machine are identical. They all have an outer

circumference of 10 cm and an inner shaft circumference of 5 cm.If the crank is rotated one quarter turn counterclockwise, wherewill the clock’s hand point?

Name _______________________________________________ Date ________________ Class______________

SCIENCE PUZZLERS, TWISTERS & TEASERS8

Work and Machines

CHAPTER

Don’t Keep It Simple1. Build your own Rube Goldberg machine that lifts a shoe

at least 30 cm, waters a plant, turns off an alarm clock, orperforms another simple action. Be creative in your choiceof materials, but be sure they are not flammable or haz-ardous. The machine should perform at least five steps toaccomplish its task. Try to keep your machine compact—it shouldn’t be bigger than 1 m3. Use as many simplemachines as you can in your Rube Goldberg machine.Compete with your classmates to see who can be the mostcreative and use the most steps.

Another Long-Term Project Idea2. Wind power is one of the most promising sources of

pollution-free energy for the future. Research windmilldesigns that have been used throughout history in differ-ent parts of the world. Build models of different wind-mills, and find out which designs work best for certaintasks. Consider the following questions: How have wind-mill designs changed? Where and how are windmills beingused today? Write this information on note cards, andattach them to your models.

Research Idea3. Did you know that some bicycles built in the 1800s

had wooden wheels and iron tires? These bikes were souncomfortable to ride that they were called “bone-shakers.”Research the history of the bicycle. What were the earlybicycle designs? When was the first “modern” bicyclebuilt? What variations have there been on the modernbicycle? How could current bicycle designs be improved?Draw a series of diagrams of bicycles, from the earliestmodels through today’s models. Include your design forthe “bike of the future.”

Name ___________________________________________________ Date _________________ Class _____________

PROJECT

STUDENT WORKSHEET58

To Complicate Things

PH

YSIC

AL S

CIE

NC

E

▼▼▼

Rube Goldberg was a cartoonist famous for drawing elaborate, complicatedmachines that accomplished simple tasks. His work was so unique and well likedthat his name is used to describe all machines that are similar to the ones hedrew. There are even contests to see who can design and build the most elabo-rate Rube Goldberg machines. A good Rube Goldberg machine uses many com-plex steps to complete a task that would normally take only one or two steps.For instance, a machine designed to turn on a light switch might involve rollingbowling balls, burning candles, jumping frogs, popping rubber bands, andspilling water. The more complicated Rube Goldberg machines are, the better.

TEACHER-LED DEMONSTRATION

DEMO

48

Purpose

Students observe how a simple machinecan make work easier.

Time Required

5–10 minutes

What to Do

1. Ask two students to hold the broomshorizontally about 50 cm apart.

2. Tie the rope or cord to one broom, andwrap it around the handles as shown.

3. Invite a third student to hold the freeend of the rope. Ask the class: Do youthink the third student can pull thebrooms together while the other twoare holding them apart? Why or whynot? (Expected answer: No; two studentsshould be able to exert more force thanone.)

4. Tell the student holding the rope topull on it. The two brooms will movetogether even while the other two stu-dents try to keep them apart.

Explanation

The brooms and rope act together to forma pulley system. A pulley is a simple ma-chine that can be used to increase a force.The force of the student pulling the ropewas multiplied by the number of pointswhere the rope pulled on the broom.Therefore, the third student exerted aforce that was five times that of each ofthe other students.

Pull-ease, Please!

MATERIALS

• 2 identical brooms• rope or strong cord, about 3 m long• metric ruler or measuring tape

Pull this end

TEACHER PREP

CONCEPT LEVEL

CLEAN UP

E A S Y H A R D

Lab Ratings

Richard PetittBardstown Middle School

Bardstown, Kentucky

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

GENERAL

GENERAL

GENERALGENERAL

GENERAL

GENERAL

GENERAL

GENERAL

SPECIAL NEEDS

SPECIAL NEEDS GENERAL

GENERAL

SAMPLE

SAMPLE SAMPLE

SAMPLE SAMPLE

SAMPLE

SAMPLE

SAMPLE

SAMPLESAMPLE

SAMPLE

SAMPLE

SAMPLE

SAMPLE

SAMPLE

SAMPLE

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

Is That a Fact!

Is That a Fact!

What Is a Machine?Leonardo da Vinci (1452–1519)• Leonardo da Vinci was an Italian painter, sculptor,

and inventor. The motivating interest behind allof his work was the appearance of everyday thingsand the way they operated. He studied the flight ofbirds, the movement of water, the growth of plants,and the anatomy of the human body.

• One of da Vinci’s interests was the mechanical advan-tage that could be obtained with gears. Da Vinci madedrawings of complex machines that were centuriesahead of their time. Among his drawings were plansfor tanks, a helicopter, and other aircraft. He wasespecially concerned with the problems of frictionand resistance. He described and drew screws,gears, hydraulic jacks, transmission gears, andswiveling devices.

• Da Vinci thought that the basic laws of mechanicsoperated the same way in all aspects of the worldand were the keys to understanding the world andreproducing it through art.

◆ Many industrial towns in early America were locatedwhere water flow could be assured all year. Water andwind were the primary sources of mechanical energyuntil the end of the 18th century, when steam powerwas developed. Steam-powered mechanical deviceslaunched the Industrial Revolution.

Chapter Enrichment

This Chapter Enrichment provides relevant and

interesting information to expand and enhance

your presentation of the chapter material.

Work and PowerJames Prescott Joule (1818–1889)• James Joule was an English physicist who established

that mechanical energy, electrical energy, and thermalenergy are basically the same and that one type ofenergy can be converted into another. This principleis the basis of the first law of thermodynamics, theconservation of energy. It states that the total energyin any closed system remains the same, even when theenergy is converted from one type to another.

• Joule developed mathematical equations that describedthe thermal energy of current in electrical wire andthe amount of work needed to produce a unit ofthermal energy. The standard unit of work and energyis called the joule and was named in Joule’s honor.

Converting Energy• In physics, energy is the ability to do

work. Energy can exist in differ-ent forms, such as thermal,electrical, nuclear, potential,kinetic, and chemical. Allforms of energy haveto do with motionor position. Energycan be convertedfrom one form toanother. For example, electrical energy is usuallyconverted from chemical, nuclear, or mechanical energy.

◆ The term horsepower was coined in the late 18thcentury by Scottish engineer James Watt, who usedhorses as a measure of power in his experiments.In the English system, 1 horsepower can accomplish33,000 foot-pounds of work per minute, or allow oneto exert the force necessary to lift 33,000 lb by 1 ft in1 min. This unit was based on the draft horse, a horseadapted for pulling heavy loads.

207E Chapter 8 • Work and Machines

8

Is That a Fact!

For background information about teaching strategies and

issues, refer to the Professional Reference for Teachers.

Perpetual Motion• For centuries, inventors have tried to build a perpetual-

motion machine—a device that would run forever once it is set in motion. However, no such machines can work because the laws of thermodynamics would be violated.

• A perpetual-motion machine would have to deliver as much or more energy than is put into it. The first law of thermodynamics states that the total energy of a closed system is constant. The second law states that some energy is always lost as thermal energy from a closed system when energy is used to do work. The practical effect of these two laws is that the output energy from any machine will never be as great asthe energy put into it.

• Friction—in which kinetic energy is converted to thermal energy—can be reduced but never eliminated. Although some machines can be made to run very efficiently, they will always need a source of energy to operate, and they will never be able to produce more energy than is put into them.

Types of MachinesThe Invention of Machines• The first machines were tools used by prehistoric

people to help them hunt and gather food. A wedge shaped out of stone made an excellent cutting tool. Early axes were wedges made of stone. Levers were used in hoes, oars, and slings. Because simple ma-chines multiply force or distance, they provided our early ancestors with a tremendous survival advantage.

The Plow• The plow was one of the first agricultural machines

to be invented, and it is still one of the most impor-tant. Evidence shows that plows first appeared more than 6,000 years ago. The first plow was not much more than a digging stick drawn by a person or an animal. As primitive as it was, the plow allowed people to dig deeper to turn over and loosen the soil. This simple machine magnified the effort of a single person enough to produce food for many people.

◆ Tiny machines are being built with gears and levers so small they can be seen only under a powerful microscope. Scientists are learning how to make even tinier machines out of molecules. Tiny gears have been shaped out of strands of DNA molecules, and hydrogen molecules may one day control microscopic computers.

Topic: Work and PowerSciLinks code: HSM1675

Topic: Mechanical EfficiencySciLinks code: HSM0929

Topic: Simple MachinesSciLinks code: HSM1395

Topic: Compound MachinesSciLinks code: HSM0331

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

Developed and maintained by theNational Science Teachers Association

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

Chapter 8 • Chapter Enrichment 207F

OverviewThis chapter describes the rela-tionship between energy andwork, the way machines dowork, and the different types ofsimple and compoundmachines.

Assessing PriorKnowledgeStudents should be familiarwith the following topics:

• matter

• forces

• motion

IdentifyingMisconceptionsAs students learn the conceptsin this chapter, they willencounter the scientific usageof the word work. Students willneed to learn the meaning ofwork in terms of force appliedover a distance instead of interms of effort expended.Students may also have to over-come the common usage of theword machine, which connotes alarge and complicated apparatus,such as a car engine. Studentsmay be slow to consider a sim-ple device, such as a lever, to bea machine.

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

Section 1 Work and PowerUCP 3; SAI 1, 2; PS 3a

Section 2 What Is a Machine?UCP 3; SAI 1, 2; ST 2

Section 3 Types of MachinesUCP 3, 5; SAI 1; ST 1, 2; LabBook: SAI 1

Chapter Lab A Powerful WorkoutSAI 1, 2; PS 3a; ST 2

Chapter ReviewSAI 1; PS 3a; ST 2

Science in ActionSAI 1, 2

Standards Correlations

208 Chapter 8 • Work and Machines

PRE-READINGPRE-READING

Work and Machines

About the

“One, two, stroke!” shouts the coach as theteam races to the fi nish line. This paddlingteam is competing in Hong Kong’s annualDragon Boat Races. The Dragon Boat Festivalis a 2,000-year-old Chinese tradition thatcommemorates Qu Yuan, a national hero.The paddlers that you see here are usingthe paddles to move the boat forward. Eventhough they are celebrating by racing theirdragon boat, in scientifi c terms, this team isdoing work.

Booklet Before you readthe chapter, create theFoldNote entitled “Booklet”

described in the Study Skills sectionof the Appendix. Label each page ofthe booklet with a main idea from thechapter. As you read the chapter, writewhat you learn abouteach main idea on theappropriate page of thebooklet.

SECTION

Work is the transfer of energyto an object, and power isthe rate at which work isdone. Machines are devicesthat help make work easier.

8

1 Work and Power . . . . . . . . . . . 210

2 What Is a Machine? . . . . . . . . . 216

3 Types of Machines . . . . . . . . . . 222

8

START-UPC’mon, Lever a Little!In this activity, you will use a simple machine, alever, to make your task a little easier.

Procedure1. Stack two books, one on top of the other, on

a table.

2. Slide your index finger underneath the edge of thebottom book. Using only the force of your finger,try to lift one side of the books 2 or 3 cm off thetable. Is it hard to do so? Write your observations.

3. Slide the end of a wooden ruler underneath theedge of the bottom book. Then, slip a large pencileraser or similar object under the ruler.

4. Again, using only your index finger, push downon the edge of the ruler and try to lift the books.Record your observations. Caution: Push downslowly to keep the ruler and eraser from flipping.

Analysis1. Which was easier: lifting the books with your fin-

ger or lifting the books with the ruler? Explain youranswer.

2. In what way did the direction of the force thatyour finger applied on the books differ from thedirection of the force that your finger applied onthe ruler?

Would YouBelieve . . . ?

The Great Pyramid was built over4,000 years ago and remains oneof the Seven Wonders of the World.

The Great Pyramid, located in Giza(GEE zuh), Egypt, could be called thelargest tombstone ever created. A mon-ument and tomb for the pharaoh KingKhufu (KOO foo), it covers an area thesize of seven city blocks and rises about40 stories high. The Great Pyramid isthe largest of the three pyramids ofGiza. It was built around 2600 BCE andtook less than 30 years to complete—arelatively short period of time consid-ering that construction equipment didn’texist 4,000 years ago. So how did theEgyptians do it?

To build the Great Pyramid, theEgyptians cut and moved more than 2million stone blocks, most averaging2,000 kg (probably over 40 times yourown mass). The blocks were cut from astone quarry, moved near the pyramid,and then lifted into place. To finish inless than 30 years, the Egyptians would

have had to cut, move, and lift about200 blocks per day! The Egyptians didnot have cranes, bulldozers, or any otherheavy-duty machines. What they hadwere two simple machines—the inclinedplane and the lever.

Archaeologists have found theremains of inclined planes, or ramps,made from mud, stone, and wood. TheEgyptians pushed or pulled the blocksalong these ramps to raise them to theproper height. Using ramps required lessforce than lifting the blocks straight up.In addition, notches in many blocks indi-cate that huge levers were used like giantcrowbars to lift and move the heavyblocks. The workers pushed down on thelever, and the lever pushed up on a stoneblock, lifting it into place.

The Egyptians used simple machinesto create something truly amazing. In thischapter, you’ll learn about work and howmachines can help make work easier.


Work and Machines CHAPTER STARTER

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

FOR EACH GROUP• books (2)• pencil eraser, large• ruler, wooden• table

Safety Caution: The rulersshould be fairly stiff and sturdy.Use lightweight books if neces-sary. If the books are not tooheavy and the activity is donecarefully, the rulers should notget broken.

Teacher’s Notes: The wordlever comes from the Latin wordlevare, meaning “to lift.” Thelever was one of the first simplemachines to be developed. Itis thought that tree limbs mayhave been used by early humansas pry bars to move heavy rocks.

Answers

1. Students should find that liftingthe books with the ruler waseasier because less effort (force)was required.

2. The direction of the force appliedby students’ fingers on the bookswas up, and the direction of theforce applied on the ruler wasdown. Using the ruler changedthe direction of the force.

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• Work and Machinesg

Chapter Starter TransparencyUse this transparency to help studentsbegin thinking about concepts of workand machines.

READINGSKILLS

Chapter 8 • Work and Machines 209

READING STRATEGY

Work and PowerYour science teacher has just given you tonight’s homework assignment. You have to read an entire chapter by tomorrow! That sounds like a lot of work!

Actually, in the scientific sense, you won’t be doing much workat all! How can that be? In science, workwork is done when a forcecauses an object to move in the direction of the force. In theexample above, you may have to put a lot of mental effort intodoing your homework, but you won’t be using force to moveanything. So, in the scientific sense, you will not be doingwork—except the work to turn the pages of your book!

What Is Work?The student in Figure 1 is having a lot of fun, isn’t she? Butshe is doing work, even though she is having fun. She isdoing work because she is applying a force to the bowling balland making the ball move through a distance. However, sheis doing work on the ball only as long as she is touching it.The ball will keep moving away from her after she releasesit. But she will no longer be doing work on the ball becauseshe will no longer be applying a force to it.

1

Figure 1You might be surprised to find out that bowling is work!

Transfer of EnergyOne way you can tell that the bowler in Figure 1has done work on the bowling ball is that theball now has kinetic energy. This means that theball is now moving. The bowler has transferredenergy to the ball.

Differences Between Force and WorkApplying a force doesn’t always result in workbeing done. Suppose that you help push a stalledcar. You push and push, but the car doesn’tbudge. The pushing may have made you tired.But you haven’t done any work on the car,because the car hasn’t moved.

You do work on the car as soon as the carmoves. Whenever you apply a force to an objectand the object moves in the direction of theforce, you have done work on the object.

✓✓Reading Check Is work done every time a force is applied to an object? Explain. (See the Appendix foranswers to Reading Checks.)

What You Will Learn

Determine when work is being doneon an object.Calculate the amount of work doneon an object.Explain the difference between workand power.

Vocabularywork powerjoule watt

Reading Organizer As you read thissection, make a table comparing workand power.

OverviewThis section introduces the sci-entific definitions of work andpower and explains how to cal-culate work and power.

BellringerWrite the following task forstudents on the board:

Select the activities belowthat require the least amountof work.

• carrying heavy books home

• reading a 300-page novel

• skiing for 1 h

• lifting a 45 kg mass

• holding a steel beam inplace for 3 h

• jacking up a car

Remind students to explainwhat work is being done in eachof their selected activities.

vv---------------------------------------------------g

Work in Sports Have students,in groups of three or four, selecta sport and discuss the differentways work is done in that sport.Have them estimate how muchwork is done in an averagegame. l Kinesthetic

Answer to Reading Check

No, work is done on an object only if forcemakes the object move in a direction that isparallel to the force.

1

CHAPTER RESOURCES

Chapter Resource File

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

Technology

Transparencies• Bellringer• P29 Work or Not Work?• LINK TOLINK TO LIFE SCIENCELIFE SCIENCE L80 A Pair of Muscles

in the Arm

Workbooks

Interactive Textbook Struggling Readers Struggling Readers


Force and Motion in the Same DirectionSuppose you are in the airport and late for a flight. You haveto run through the airport carrying a heavy suitcase. Becauseyou are making the suitcase move, you are doing work on it,right? Wrong! For work to be done on an object, the objectmust move in the same direction as the force. You are apply-ing a force to hold the suitcase up, but the suitcase is movingforward. So, no work is done on the suitcase. But work is doneon the suitcase when you lift it off the ground.

Work is done on an object if two things happen: (1) theobject moves as a force is applied and (2) the direction of theobject’s motion is the same as the direction of the force. Thepictures and arrows in Figure 2 will help you understand whenwork is being done on an object.

work the transfer of energy to anobject by using a force that causesthe object to move in the directionof the force

Yes

No

Yes

No

Work or Not Work?Figure 2

Example Directionof force

Directionof motion

Doing work?

SKILLWork in theHuman Body

You may not be doing anywork on a suitcase if you arejust holding it in your hands,but your body will still gettired from the effort becauseyou are doing work on themuscles inside your body. Yourmuscles can contract thou-sands of times in just a fewseconds while you try to keepthe suitcase from falling. Whatother situations can you thinkof that might involve workbeing done somewhere insideyour body? Describe these situ-ations in your science journal.

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

Prediction Guide Beforestudents read this section, askthem whether they agree withthe following statements:

1. Any time a force is applied toan object, work is being done.(false)

2. Power, work, and force arethe same. (false)

3. More power means doingwork faster. (true)

l Logical

MISCONCEPTIONALERT

Work and Force The text states that thegirl does work on the bowling ball onlywhen she is touching it. The ball con-tinues to move when she lets go of it,but she’s no longer applying a force toit. Disregarding friction, once the ball ismoving, no additional force is neededto keep it moving at constant speedbecause of Newton’s first law of motion.

SUPPORT FOR

English LanguageLearnersWork and the Direction ofForce Students will betterunderstand when work is be-ing performed if they createtheir own examples. Afterthey have read the text andchart on these pages, reviewthe examples in the chartas a class. Ask volunteers topoint out where work is beingdone and why. Then, haveeach student create a similarchart with four of their ownexamples from their everydaylives, including sports andgames. They should draweach example, specify direc-tion of force and motion witharrows, and indicate whetheror not work is being done.Emphasize to students thatthey should not just copy theinformation from the chartin the text. When charts arecompleted, ask students toexchange charts and look forany misconceptions aboutwork. Discuss these in class.l Visual/Interpersonal

Section 1 • Work and Power 211

How Much Work?Would you do more work on a car by pushing itup a long road to reach the top of a hill or byusing a cable to raise the car up the side of a cliffto the top of the same hill? You would certainlyneed a different amount of force. Common useof the word work may make it seem that therewould be a difference in the amount of workdone in the two cases as well.

Figure 4 Climbers going to thetop of a mountain do the sameamount of work whether they hikeup a slope or go straight up a cliff.

W � F1 � d1 � F2 � d2

F1

d1 F2d2

Figure 3 For each path, thesame work is done to movethe car to the top of the hill,although distance and forcealong the two paths differ.

Same Work, Different ForcesYou may be surprised to learn that the same amount of workis being done to push the car up a road as to raise it up thecliff. Look at Figure 3. A certain amount of energy is needed tomove the car from the bottom to the top of the hill. Becausethe car ends up at the same place either way, the work doneon the car is the same. However, pushing the car along theroad up a hill seems easier than lifting it straight up. Why?

The reason is that work depends on distance as well asforce. Consider a mountain climber who reaches the top of amountain by climbing straight up a cliff, as in Figure 4. Shemust use enough force to overcome her entire weight. But thedistance she travels up the cliff is shorter than the distancetraveled by hikers who reach the top of the same mountainby walking up a slope. Either way, the same amount of workis done. But the hikers going up a slope don’t need to use asmuch force as if they were going straight up the side of thecliff. This shows how you can use less force to do the sameamount of work.

StrategiesStrategiesINCLUSIONINCLUSION

• Learning Disabled• Developmentally Delayed• Visually ImpairedOn a piece of paper write theword “Force” with a thickarrow drawn underneath andmake 4 copies. On anotherpiece of paper write “Motion”with a thick arrow drawnunderneath and make 4 cop-ies. Write a large “Yes” on athird piece of paper and alarge “No” on a fourth pieceof paper and make 4 copiesof each.Divide the class into 4 teams.Give each team one Forcearrow, one Motion arrow, aYes, and a No. Assign one ofthe following tasks. Ask eachteam to determine whethertheir task is work. Have eachteam demonstrate theirassigned task, use the arrowsto show the direction of theforce and the motion, andYes or No to state whetherwork is done.Shut the door. (Both arrowsto the right; Yes.) Carry abook. (Force arrow up,motion arrow sideways; No.)Push a rolling chair. (Botharrows to the right; Yes.) Lifta book. (Both arrowsup; Yes.)l Interpersonal ee

vv--------------------------------------g

Work Done on a Spring Scale Obtain ameter stick, string, a spring scale, and vari-ous objects to lift. Organize students intopairs. Have each pair attach each object inturn to the spring scale and slowly lift orpull the object and then record how muchforce was used. Next, have them measurethe distance that the object moved andrecord the distance in meters. Have themcalculate how much work was done.l Kinesthetic


Calculating WorkThe amount of work (W) done in moving an object, such asthe barbell in Figure 5, can be calculated by multiplying theforce (F) applied to the object by the distance (d) through whichthe force is applied, as shown in the following equation:

W � F � d

Force is expressed in newtons, and the meter is the basic SIunit for length or distance. Therefore, the unit used to expresswork is the newton-meter (N � m), which is more simply calledthe joule. Because work is the transfer of energy to an object,the joule (J) is also the unit used to measure energy.

✓Reading Check How is work calculated?

The force needed to lift anobject is equal to the gravita-tional force on the object—inother words, the object’s weight.

W � 80 N � 1 m � 80 J

If you increase the weight, anincreased force is needed tolift the object. This increasesthe amount of work done.

W � 160 N � 1 m � 160 J W � 80 N � 2 m � 160 J

joule the unit used to expressenergy; equivalent to the amountof work done by a force of 1 N act-ing through a distance of 1 m in thedirection of the force (symbol, J)

Force Times DistanceFigure 5

Get to Work!1. Use a loop of string to attach a spring scale

to a weight.2. Slowly pull the weight across a table by

dragging the spring scale. Record the amountof force that you exerted on the weight.

3. Use a metric ruler to measure the distancethat you pulled the weight.

4. Now, use the spring scale to slowly pull theweight up a ramp. Pull the weight the samedistance that you pulled it across the table.

5. Calculate the work you did on the weight forboth trials.

6. How were the amounts of work and forceaffected by the way you pulled the weight? Whatother ways of pulling the weight could you test?

80 N

80 N

160 N

Increasing the distance alsoincreases the amount ofwork done.

M A T E R I A L SFOR EACH STUDENT

• ramp• ruler, metric• scale, spring• string, loop• table• weight

Teacher’s Note: Be sure thatstudents pull the weight witha constant speed. Theyshould also keep the springscale parallel to the tabletopor ramp when pulling.

Answer

6. Sample answer: More forcewas needed to pull the weightacross the ramp than to pull itacross the table. Therefore,more work was done whenpulling the weight across theramp. Other ways of pullingthe weight might includeusing a much steeper ramp orpulling the weight straight upa vertical surface.


Work is calculated as force timesdistance.


Transparencies• P30 Force Times Distance

Workbooks

Math Skills for Science• Work and Powerg

Q: Did you hear about the criminals who

never had to do any work?

A: They were joule thieves.


Power: How Fast Work Is DoneLike the term work, the term power is used a lot in everydaylanguage but has a very specific meaning in science. Power isthe rate at which energy is transferred.

Calculating PowerTo calculate power (P), you divide the amount of work done(W) by the time (t) it takes to do that work, as shown in thefollowing equation:

The unit used to express power is joules per second (J/s),also called the watt. One watt (W) is equal to 1 J/s. So if youdo 50 J of work in 5 s, your power is 10 J/s, or 10 W.

Power measures how fast work happens, or how quicklyenergy is transferred. When more work is done in a givenamount of time, the power output is greater. Power output isalso greater when the time it takes to do a certain amount ofwork is decreased, as shown in Figure 6.

✓Reading Check How is power calculated?

power the rate at which work isdone or energy is transformed

watt the unit used to expresspower; equivalent to joules persecond (symbol, W)

More Power to You A stage manager at a playraises the curtain by doing 5,976 J of work onthe curtain in 12 s. What is the power outputof the stage manager?

Step 1: Write the equation for power.

Step 2: Replace W and t with work and time.

Now It’s Your Turn1. If it takes you 10 s to do 150 J of work

on a box to move it up a ramp, whatis your power output?

2. A light bulb is on for 12 s, and duringthat time it uses 1,200 J of electricalenergy. What is the wattage (power) ofthe light bulb?

Figure 6 No matter how fast youcan sand by hand, an electricsander can do the same amount ofwork faster. Therefore, the electricsander has more power.

P �Wt

P �Wt

P � � 498 W5,976 J

12 s

Reteaching -------------------------------------bWork and Power After studentsread the section on work andpower, discuss with students theuse of the words work and powerin everyday language. Identifyusages that do not match thescientific definition of work,and discuss why the two usagesare different.l Verbal ee

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

1. What are the two things thatmust happen for work to bedone? (A force must be exertedon an object, and the object mustmove in the direction of theforce.)

2. You use 75 N of force to pusha box 3 m across the floor.How much work has beendone? (225 J)

3. What is the power of a smallmotor that can do 4,500 J ofwork in 25 s? (180 W)

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

Concept Mapping Have stu-dents create a concept mapusing the words work, force,distance, power, and time in away that matches their scientificdefinitions. l Visual


Power is calculated as work done (in joules)divided by the time (in seconds) in which thework was done.

Answers to Math Focus

1. 150 J � 10 s �15 W2. 1,200 J � 12 s �100 W

Q: What is the unit of power?

A: Watt.

Q: I said, What is the unit of power?

A: Watt!

Q: I SAID . . .


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

SummarySummary

W � F1 � d1 � F2 � d2

F1

d1 F2d2

Review

Increasing PowerIt may take you longer to sand a wooden shelf by hand thanby using an electric sander, but the amount of energy neededis the same either way. Only the power output is lower whenyou sand the shelf by hand (although your hand may getmore tired). You could also dry your hair with a fan, but itwould take a long time! A hair dryer is more powerful. It cangive off energy more quickly than a fan does, so your hairdries faster.

Car engines are usually rated with a certain power output.The more powerful the engine is, the more quickly the enginecan move a car. And for a given speed, a more powerful enginecan move a heavier car than a less powerful engine can.

• In scientific terms, workis done when a forcecauses an object tomove in the directionof the force.

• Work is calculated asforce times distance.The unit of work is thenewton-meter, or joule.

• Power is a measure ofhow fast work is done.

• Power is calculated aswork divided by time.The unit of power isthe joule per second,or watt.

Using Key Terms

For each pair of terms, explain howthe meanings of the terms differ.

1. work and joule

2. power and watt

Understanding Key Ideas

3. How is work calculated?

a. force times distanceb. force divided by distancec. power times distanced. power divided by distance

4. What is the difference betweenwork and power?

Math Skills

5. Using a force of 10 N, you pusha shopping cart 10 m. Howmuch work did you do?

6. If you did 100 J of work in 5 s,what was your power output?

Critical Thinking

7. Analyzing Processes Work isdone on a ball when a pitcherthrows it. Is the pitcher stilldoing work on the ball as it fliesthrough the air? Explain.

8. Applying Concepts You lifta chair that weighs 50 N to aheight of 0.5 m and carry it10 m across the room. Howmuch work do you do onthe chair?

Interpreting Graphics

9. What idea about work and forcedoes the following diagramdescribe? Explain your answer.

Topic: Work and PowerSciLinks code: HSM1675

WRITING

SKILLHorsepower Theunit of power most

commonly used to rate carengines is the horsepower(hp). Look up the word horse-power in a dictionary. Howmany watts is equal to 1 hp?Do you think all horsesoutput exactly 1 hp? Why orwhy not? Write your answersin your science journal.

Answers to Section Review

1. Sample answer: Work occurswhen a force causes an objectto move in the direction of theforce. Joule is the unit in whichwork is measured.

2. Sample answer: Power is therate at which work is done.Watt is the unit in which poweris measured.

3. a4. Work is done when a force

causes an object to move in thedirection of the force, and poweris the rate at which work is done.

5. 10 N � 10 m � 100 J6. 100 J � 5 s � 20 W7. no; Once the ball leaves the

pitcher’s hand, work is no longerbeing done on the ball. Themotion of the ball after that pointis due to the kinetic energyalready given to the ball by thepitcher.

8. 50 N � 0.5 m � 25 J; No furtherwork has been done on the chaironce it has been lifted, becausethe direction in which you walkis perpendicular to the directionin which you lifted the chair.

9. The diagram describes the factthat for either path taken, thesame work is done on an object,although distance and forcebetween the two paths vary.

CHAPTER RESOURCES


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


READING STRATEGY

What Is a Machine?You are in the car with your mom on the way to a party when suddenly—KABLOOM hisssss—a tire blows out. “Now I’m going to be late!” you think as your mom pulls over to the side of the road.

You watch as she opens the trunk and gets out a jack and a tireiron. Using the tire iron, she pries the hubcap off and beginsto unscrew the lug nuts from the wheel. She then puts the jackunder the car and turns the jack’s handle several times untilthe flat tire no longer touches the ground. After exchangingthe flat tire with the spare, she lowers the jack and puts thelug nuts and hubcap back on the wheel.

“Wow!” you think, “That wasn’t as hard as I thought itwould be.” As your mom drops you off at the party, you thinkhow lucky it was that she had the right equipment to changethe tire.

Machines: Making Work EasierNow, imagine changing a tire without the jack and the tireiron. Would it have been easy? No, you would have neededseveral people just to hold up the car! Sometimes, you need thehelp of machines to do work. A machinemachine is a device that makeswork easier by changing the size or direction of a force.

When you think of machines, you might think of thingssuch as cars, big construction equipment, or even computers.But not all machines are complicated. In fact, you use manysimple machines in your everyday life. Figure 1 shows someexamples of machines.

Ch

Scissors

Wheelchair

2

Figure 1

What You Will Learn

Explain how a machine makeswork easier.Describe and give examples of theforce-distance trade-off that occurswhen a machine is used.Calculate mechanical advantage.Explain why machines are not100% efficient.

Vocabularymachinework inputwork outputmechanical advantagemechanical efficiency

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

OverviewThis section explains howmachines make work easier. Italso explains how to calculateand compare the mechanicaladvantage of machines and themechanical efficiency ofmachines.

BellringerPose the following question toyour students, and have themwrite a one-paragraph answerin their science journal: “Whydo we use machines?”

Discussion ----------------------------------gExamples of Machines Showstudents a selection of picturesof familiar objects that representsimple machines either alone orin combination. Discuss withstudents how each of the objectscan be used to make work easier.Later, when simple machines areintroduced, you can have stu-dents identify the simplemachines in each picture.l Visual

CONNECTIONCONNECTION vvHome Economics---------g

Kitchen Utensils as Machines Show stu-dents some common kitchen utensils, suchas knives, forks, can and bottle openers,nutcrackers, and manual eggbeaters. Allowstudents to examine the utensils and dis-cuss their uses. Then, have students specu-late how each machine makes work easier.l Visual

2

CHAPTER RESOURCES



Technology

Transparencies• Bellringer

Workbooks



Work In, Work OutSuppose that you need to get the lid off a can of paint. Whatdo you do? One way to pry the lid off is to use a commonmachine known as a lever. Figure 2 shows a screwdriver beingused as a lever. You place the tip of the screwdriver underthe edge of the lid and then push down on the screwdriver’shandle. The tip of the screwdriver lifts the lid as you pushdown. In other words, you do work on the screwdriver, andthe screwdriver does work on the lid.

Work is done when a force is applied through a distance.Look again at Figure 2. The work that you do on a machineis called work input. You apply a force, called the input force,to the machine through a distance. The work done by themachine on an object is called work output. The machine appliesa force, called the output force, through a distance.

How Machines HelpYou might think that machines help you because theyincrease the amount of work done. But that’s not true. If youmultiplied the forces by the distances through which the forcesare applied in Figure 2 (remember that W � F � d), you wouldfind that the screwdriver does not do more work on the lidthan you do on the screwdriver. Work output can never begreater than work input. Machines allow force to be appliedover a greater distance, which means that less force will beneeded for the same amount of work.

✓Reading Check How do machines make work easier? (See theAppendix for answers to Reading Checks.)

machine a device that helps dowork by either overcoming a force orchanging the direction of the appliedforce

Figure 2 When you use amachine, you do work on themachine, and the machine doeswork on something else.

work input the work done on amachine; the product of the inputforce and the distance through whichthe force is exerted

work output the work done by amachine; the product of the outputforce and the distance through whichthe force is exerted

Output force

Input force

READINGSTRATEGY --------------------b

Concept Mapping Havestudents begin constructinga concept map of this sectionand continue it as they progressthrough the section. They shouldillustrate at least half the bubbleswith their own drawings orphotographs from magazines.The illustrations should elabo-rate on or relate to the ideasincluded in the map. l Visual

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

Benefits and Drawbacks ofMachines Encourage a studentdebate about the benefits anddrawbacks of machines since theIndustrial Revolution. Studentsshould understand that althoughmachines have many benefits,machines may bring problems,such as pollution and workplaceinjuries. l Interpersonal

Using ScienceFiction---------------------------------------------------------a

Have students read the story“Clean Up Your Room!” byLaura Anne Gilman in the HoltAnthology of Science Fiction. Asyou discuss the story, ask stu-dents to compare the positiveand negative aspects of tech-nology in our lives. l Verbal


Machines make work easier by allowing forceto be applied over a greater distance.

It is a physical law that the work outputof a machine is always less than the workinput, yet people continue to try toinvent machines that will run forever.Known as perpetual-motion machines,these devices promise unlimitedoperation but can never deliver becausethey violate the laws of physics.

Section 2 • What Is a Machine? 217

Same Work, Different ForceMachines make work easier by changing the size or direction(or both) of the input force. When a screwdriver is used as alever to open a paint can, both the size and direction of theinput force change. Remember that using a machine does notchange the amount of work you will do. As Figure 3 shows,the same amount of work is done with or without the ramp.The ramp decreases the size of the input force needed to liftthe box but increases the distance over which the force isexerted. So, the machine allows a smaller force to be appliedover a longer distance.

The Force-Distance Trade-OffWhen a machine changes the size of the force, the distancethrough which the force is exerted must also change. Forceor distance can increase, but both cannot increase. When oneincreases, the other must decrease.

Figure 4 shows how machines change force and distance.Whenever a machine changes the size of a force, the machinealso changes the distance through which the force is applied.Figure 4 also shows that some machines change only thedirection of the force, not the size of the force or the distancethrough which the force is exerted.

✓Reading Check What are the two things that a machine canchange about how work is done?

W = 450 N × 1 m = 450 J W = 150 N × 3 m = 450 J

Lifting this box straight up requires aninput force equal to the weight of the box.

Using a ramp to lift the box requires an input force less thanthe weight of the box, but the input force must be exertedover a greater distance than if you didn’t use a ramp.

Input Force and DistanceFigure 3

For another activity relatedto this chapter, go togo.hrw.com and type in thekeyword HP5WRKW.

vv---------------------------------------------------a

Machines as Solutions toProblems Have students thinkof a problem that has no appar-ent solution. The problem mayalso be something that studentsthink may become a problem inthe future. Challenge them toinvent a machine that solvesthat problem. Have themdescribe it as carefully as possi-ble and illustrate it with theirown artwork. l Logical

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

Graphing Force and DistanceA certain task takes 480 J ofwork. Remind students thatmany combinations of F � dresult in 480 J of work (480 N �

1 m or 64 N � 7.5 m). Help stu-dents find combinations offorces and distances whose prod-ucts are 480 J. Have them usethese number pairs to plot andconnect points on a graph (withF on the x-axis and d on they-axis). Discuss what the graphsshow about the relationshipbetween force and distance.(F and d are inversely related.)Students can start with any twoof the quantities, calculate thethird, and then make thegraph. l Visual

h-----------------------------g

Everyday Use of Machines Have studentskeep a “machine diary” for a week. Eachday, they should describe the machinesthey used or came into contact with overthe course of the day. Have them expandtheir ideas of what a machine is by exam-ining ordinary actions such as writing orplaying and deciding whether a machineis involved. l Intrapersonal


Machines can change the force or the distancethrough which force is applied.


Mechanical AdvantageSome machines make work easier than others do because theycan increase force more than other machines can. A machine’smechanical advantage is the number of times the machinemultiplies force. In other words, the mechanical advantagecompares the input force with the output force.

Calculating Mechanical AdvantageYou can find mechanical advantage by using the followingequation:

For example, imagine that you had to push a 500 N weightup a ramp and only needed to push with 50 N of force theentire time. The mechanical advantage of the ramp would becalculated as follows:

A machine that has a mechanical advantage that is greaterthan 1 can help move or lift heavy objects because theoutput force is greater than the input force. A machine thathas a mechanical advantage that is less than 1 will reduce theoutput force but can increase the distance an object moves.Figure 4 shows an example of such a machine—a hammer.

mechanical advantage a numberthat tells how many times a machinemultiplies force

A simple pulleychanges thedirection of theinput force, but thesize of the outputforce is the same asthe input force.

A hammerdecreases theforce, but appliesit over a greaterdistance.

When a screw-driver is usedas a lever,it increasesthe force anddecreases thedistance overwhich the forceis applied.

A nutcrackerincreasesthe force butapplies it overa shorterdistance.

Machines Change the Size and/or Direction of a ForceFigure 4

Outputforce

Inputforce

Input force

Outputforce

Inputforce

OutputforceInput

force

Outputforce

mechanical advantage (MA) � input forceoutput force

MA � � 10500 N50 N

Finding the AdvantageA grocer uses a handcart tolift a heavy stack of cannedfood. Suppose that he appliesan input force of 40 N to thehandcart. The cart applies anoutput force of 320 N to thestack of canned food. What isthe mechanical advantage ofthe handcart?

CONNECTIONCONNECTION vvHistory ----------------------------------------------------------------g

PORTFOLIO

Prehistoric MachinesHave students research

prehistoric uses of machines,especially the earliest occur-rences of machines that changethe size or direction of a force inthe same ways that the examplesin Figure 4 do. l Logical

Answers to Math Practice

MA � 320 N � 40 N � 8

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

Animals Using Tools Humans aren’t theonly animals that use tools. Chimpanzeesfashion specialized twigs to snare termitesfrom inside their mounds, and some ottersuse carefully selected rocks to crack openshellfish. The use of tools is considered adistinct evolutionary advantage. Have stu-dents find information about such tool useand make some creative presentations tothe class. l Verbal


Transparencies• P30 Input Force and Distance• P31 Machines Change the Size and/or Direction

of a Force

Workbooks

Math Skills for Science• Mechanical Advantageg

SUPPORT FOR

English LanguageLearnersMachines and Force Visualaids may help students un-derstand the different effectsmachines can have on force.Provide pairs of studentspictures of several types ofmachines, such as those usedin construction or industry.Draw a two-circle Venn dia-gram on the board, and labelthe circles size and direction.Have one student from eachpair copy the diagram onto asheet of paper. Ask studentsto analyze whether each ma-chine changes the size or thedirection (or both) of a force,and tape the picture in thecorrect place on the diagram.Remind students that ma-chines affecting both size anddirection of forces should beplaced in the circles’ overlap.When students have finished,ask them to show their dia-grams to the class and brieflyexplain their reasons forplacements.l Visual/Logical


Mechanical EfficiencyThe work output of a machine can never be greater than the work input. In fact, the work output of a machine is always less than the work input. Why? Some of the work done by the machine is used to overcome the friction created by the use of the machine. But keep in mind that no work is lost. The work output plus the work done to overcome friction is equal to the work input.

The less work a machine has to do to overcome fric-tion, the more efficient the machine is. Mechanical efficiency(muh KAN i kuhl e FISH uhn see) is a comparison of a machine’s work output with the work input.

Calculating EfficiencyA machine’s mechanical efficiency is calculated using the following equation:

The 100 in this equation means that mechanical efficiency is expressed as a percentage. Mechanical efficiency tells you what percentage of the work input gets converted into work output.

Figure 5 shows a machine that is used to drill holes in metal. Some of the work input is used to overcome the friction between the metal and the drill. This energy cannot be used to do work on the steel block. Instead, it heats up the steel and the machine itself.

✓Reading Check How is mechanical efficiency calculated?

Useful FrictionFriction is always present when two objects touch or rub together, and friction usually slows down mov-ing parts in a machine and heats them up. In some cases, parts in a machine are designed to increase friction. While at home, observe three situations in which friction is useful. Describe them in your science journal.

Figure 5 In this machine, some of the work input is converted into sound and heat energy.

mechanical efficiency a quantity, usually expressed as a percentage, that measures the ratio of work output to work input; it can be calculated by dividing work output by work input

mechanical efficiency �work inputwork output

� 100


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

Design of Machines For each of the examples of machines in Figure 4 on the previous page, have students design a different machine that would accomplish the same job. The machine can be as simple or as elaborate as desired. Does the new machine change force in the same way as the original? l Visual

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

1. How does a machine make work easier? (by changing the size or direction (or both) of a force)

2. What two things do you need to know in order to calculate mechanical efficiency? (workinput and work output)

3. If the mechanical advantage of a machine is 5, how does the output force compare with the input force? (The output force is 5 times greater than the input force.)

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

Rube Goldberg Machines Show students one of Rube Goldberg’s cartoons. Ask them to decipher what is happening in the car-toon. Focus students’ attention on the action in each step and the results of the action. Challenge students to design and draw their own machine that uses multiple steps to per-form a simple task. l Logical Answer to Reading Check

mechanical efficiency � (work output �

work input) � 100


SummarySummary

Review

Perfect Efficiency?An ideal machine would be a machine that had 100%mechanical efficiency. An ideal machine’s useful workoutput would equal the work done on the machine. Idealmachines are impossible to build, because every machinehas moving parts. Moving parts always use some of thework input to overcome friction. But new technologieshelp increase efficiency so that more energy is availableto do useful work. The train in Figure 6 is floating onmagnets, so there is almost no friction between the trainand the tracks. Other machines use lubricants, such asoil or grease, to lower the friction between their movingparts, which makes the machines more efficient.

• A machine makes workeasier by changing thesize or direction (orboth) of a force.

• A machine can increaseforce or distance, butnot both.

• Mechanical advantagetells how many times amachine multiplies force.

• Mechanical efficiencyis a comparison of amachine’s work outputwith work input.

• Machines are not 100%efficient because someof the work done is usedto overcome friction.

Using Key Terms

For each pair of terms, explain howthe meanings of the terms differ.

1. work input and work output

2. mechanical advantage andmechanical efficiency


3. Which of the following isthe correct way to calculatemechanical advantage?

a. input force � output forceb. output force � input forcec. work input � work outputd. work output � work input

4. Explain how using a rampmakes work easier.

5. Give a specific example of amachine, and describe how itsmechanical efficiency mightbe calculated.

6. Why can’t a machine be100% efficient?

Math Skills

7. Suppose that you exert 60 N on amachine and the machine exerts300 N on another object. Whatis the machine’s mechanicaladvantage?

8. What is the mechanicalefficiency of a machine whosework input is 100 J and workoutput is 30 J?

Critical Thinking

9. Making Inferences For amachine with a mechanicaladvantage of 3, how does thedistance through which theoutput force is exerted differfrom the distance throughwhich the input force is exerted?

10. Analyzing Processes Describethe effect that friction has on amachine’s mechanical efficiency.How do lubricants increase amachine’s mechanicalefficiency?

Topic: Mechanical EfficiencySciLinks code: HSM0929

Figure 6 There is very little frictionbetween this magnetic levitation trainand its tracks, so it is highly efficient.


1. Sample answer: Work input isthe work done on a machine.Work output is the work doneby a machine.

2. Sample answer: Mechani caladvantage is the numberof times a machine multipliesforce. Mechanical efficiencymeasures the ratio of workoutput to work input.

3. b4. A ramp allows you to lift

something by pushing it a lon-ger distance using less force.

5. Sample answer: an elevator;Its work output could bemeasured by the weight anddistance a load is carriedupward, and its work inputcould be measured by theelectrical energy it uses to dothat work. You would thendivide the work output by thework input and multiply by 100to get a percentage: themechanical efficiency.

6. Machines have moving partsin which friction causes energyinput to be lost as heat.

7. MA � 300 N � 60 N � 58. ME � (30 J � 100 J) �

100 � 30 %9. Sample answer: The output

force would be applied througha distance one-third that of thedistance that the input force isapplied.

10. Sample answer: Lubricantsdecrease the friction in amachine, thereby allowingmore of the work input to beconverted to work output.

CHAPTER RESOURCES


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


Inputforce

Fulcrum

Outputforce

Load

READING STRATEGY

Types of MachinesImagine that it’s a hot summer day. You have a whole ice-cold watermelon in front of you. It would taste cool and delicious—if only you had a machine that could cut it!

The machine you need is a knife. But how is a knife a machine?A knife is actually a very sharp wedge, which is one of thesix simple machines. The six simple machines are the lever,the inclined plane, the wedge, the screw, the pulley, and thewheel and axle. All machines are made from one or more ofthese simple machines.

LeversHave you ever used the claw end of a hammer to remove anail from a piece of wood? If so, you were using the ham-mer as a lever. A leverlever is a simple machine that has a barthat pivots at a fixed point, called a fulcrum. Levers are usedto apply a force to a load. There are three classes of levers,which are based on the placements of the fulcrum, the load,and the input force.

First-Class LeversWith a first-class lever, the fulcrum is between the input forceand the load, as shown in Figure 1. First-class levers alwayschange the direction of the input force. And depending onthe location of the fulcrum, first-class levers can be used toincrease force or to increase distance.

When the fulcrum is closer to the load than to the input force, the lever has a mechanical advan-tage of greater than 1. The out-put force is increased because it is exerted over a shorter distance.

When the fulcrum is exactly in the middle, the lever has amechanical advantage of 1.The output force is not increased because the input force’s distance is not increased.

When the fulcrum is closer to the input force than to the load, the lever has a mechanical advan-tage of less than 1. Although the output force is less than the input force, distance increases.

Examples of First-Class LeversFigure 1

3What You Will Learn

Identify and give examples of the sixtypes of simple machines.Analyze the mechanical advantageprovided by each simple machine.Identify the simple machines thatmake up a compound machine.

Vocabularylever wedgepulley screwwheel and compound

axle machineinclined plane

Mnemonics As you read thissection, create a mnemonic deviceto help you remember the differenttypes of levers.

OverviewThis section describes the sixsimple machines and explainshow to determine the mechani-cal advantage of each. Studentslearn about compound ma-chines and combinations of sim-ple machines they commonlyencounter, and they learn howcombining simple machinesaffects efficiency.

BellringerPose the following question tostudents: What type of machinecan be found on at least half thestudents in this room right now?(zipper)

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Loads on a First-Class LeverOrganize the class into smallgroups. Have each group use astring to hang a meterstick froma ring. The meterstick should bebalanced until it hangs level.Then, ask the groups to tie fivelarge metal washers tied togetherto the meterstick at the 2 cmmark. Challenge them to find away to again balance the meter-stick without adding anyweights to the opposite end.Discuss the students’ solutionsto the problem. l Kinesthetic

3

CHAPTER RESOURCES



Technology

Transparencies• Bellringer

Workbooks



Fulcrum

Outputforce

Inputforce

Load

Fulcrum

Outputforce

Inputforce

Load

Second-Class LeversThe load of a second-class lever is between the fulcrum andthe input force, as shown in Figure 2. Second-class levers donot change the direction of the input force. But they allowyou to apply less force than the force exerted by the load.Because the output force is greater than the input force, youmust exert the input force over a greater distance.

Third-Class LeversThe input force in a third-class lever is between the fulcrumand the load, as shown in Figure 3. Third-class levers do notchange the direction of the input force. In addition, they donot increase the input force. Therefore, the output force isalways less than the input force.

✓Reading Check How do the three types of levers differ fromone another? (See the Appendix for answers to Reading Checks.)

lever a simple machine that con-sists of a bar that pivots at a fixedpoint called a fulcrum

In a third-class lever, the inputforce is between the fulcrum andthe load.

Using a third-class lever results in a mechanical advantage of lessthan 1 because force is decreased. But third-class levers increasethe distance through which the output force is exerted.

In a second-class lever, the outputforce, or load, is between the inputforce and the fulcrum.

Using a second-class lever results in a mechanical advantage ofgreater than 1. The closer the load is to the fulcrum, the more theforce is increased and the greater the mechanical advantage is.

Examples of Second-Class LeversFigure 2

Examples of Third-Class LeversFigure 3

Making Models--------------bSeesaws as First-ClassLevers Provide students withtriangular blocks and long piecesof wood so that they can makesmall seesaws. Have studentsexperiment with the positionand size of the weights and theplacement of the fulcrum. Havethem write their observationsand descriptions in their sci-ence journal. l Kinesthetic

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Classifying Tools Gather aselection of levers, such asbrooms, shovels, crowbars, fish-ing poles, ice or sugar-cubetongs, pliers, scissors, baseballbats, tennis rackets, hockeysticks, golf clubs, canoe paddles,boat oars, wheelbarrows, nut-crackers, tweezers, and bottleopeners. Divide the class intogroups, and assign each groupseveral tools. Have each groupwork together to locate thefulcrum, load, location ofinput force, and location ofoutput force in each lever.Then, have each group shareits information with othergroups. l Interpersonal


Each class of lever involves adifferent set of mechanical-advantage possibilities.

Is That a Fact!The human body uses simple machines.Muscles and bones form first-class andthird-class levers. When you look up,the skull pivots on the neck vertebrae,forming a first-class lever. When youkick a soccer ball, the contracting mus-cle pulls your leg upward, acting as athird-class lever.

Levers Besides being used in bottleopeners and nail pullers, levers are usedin devices such as fishing rods, cranes,typewriters, pianos, parking meters,and scales.

Section 3 • Types of Machines 223

PulleysWhen you open window blinds by pulling on a cord, you’reusing a pulley. A pulleypulley is a simple machine that has a groovedwheel that holds a rope or a cable. A load is attached to oneend of the rope, and an input force is applied to the otherend. Types of pulleys are shown in Figure 4.

Fixed PulleysA fixed pulley is attached to something that does not move.By using a fixed pulley, you can pull down on the rope tolift the load up. The pulley changes the direction of the force.Elevators make use of fixed pulleys.

Movable PulleysUnlike fixed pulleys, movable pulleys are attached to the objectbeing moved. A movable pulley does not change a force’s direc-tion. Movable pulleys do increase force, but they also increasethe distance over which the input force must be exerted.

Block and TacklesWhen a fixed pulley and a movable pulley are used together,the pulley system is called a block and tackle. The mechanicaladvantage of a block and tackle depends on the number ofrope segments.

pulleypulley a simple machine that con-sists of a wheel over which a rope, chain, or wire passes

Types of PulleysFigure 4

Fixed Pulley Block and TackleMovable Pulley

Outputforce

Inputforce

Inputforce

Outputforce

Inputforce

Outputforce

Inputforce

A fixed pulley only spins. The size of the output force is the same as the size of the input force. Therefore, a fixed pulley provides a mechanical advantage of 1.

A movable pulley movesup with the load as the load is lifted. The mechanical advantage of this movable pulley is 2.

The mechanical advantage of this block and tackle is 4 because there are four rope segments. It multiplies your input force by 4, but you have to pull the rope 4 m just to lift the load 1 m.

Using the Figure -----g

Figure 4 The mechanicaladvantage of a pulley is equal tothe number of rope segmentsthat support the load. Each ofthese supporting rope segmentsapplies a force equal to theinput force to do the work oflifting the load. For this reason,the movable pulley has twoinput force arrows. The com-bined distance through whichthose input forces are exertedis the input distance, which istwice the distance that the loadis actually lifted. l Visual

Guided Practice--------g

PORTFOLIO

Simple MachinesCollage Collect some

old magazines. After studentshave read the section on simplemachines, have them lookthrough the magazines for pic-tures of different types of simplemachines. Have students make acollage that classifies the pic-tures according to the type ofsimple machine they represent.l Visual

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

Machines in Your School Take studentsto visit the custodian’s area in the schoolbuilding. Have the custodian demonstratethe uses of different machines, and discusshow machines make the necessary tasks ofmaintaining the school building easier.l Interpersonal


Wheel

Axle

Input force

Output force

Radius of axle 3 cm

Radius of wheel 15 cm

MA � � 515 cm3 cm

Wheel and AxleDid you know that a faucet is a machine? The faucet shown inFigure 5 is an example of a wheel and axle, a simple machineconsisting of two circular objects of different sizes. Doorknobs,wrenches, and steering wheels all use a wheel and axle. Figure 5shows how a wheel and axle works.

Mechanical Advantage of a Wheel and AxleThe mechanical advantage of a wheel and axle can be foundby dividing the radius (the distance from the center to theedge) of the wheel by the radius of the axle, as shown inFigure 6. Turning the wheel results in a mechanical advantageof greater than 1 be cause the radius of the wheel is larger thanthe radius of the axle.

✓Reading Check How is the mechanical advantage of a wheeland axle calculated?

Figure 6 The mechanical advantageof a wheel and axle is the radius of thewheel divided by the radius of the axle.

wheel and axle a simple machineconsisting of two circular objects ofdifferent sizes; the wheel is the largerof the two circular objects

How a Wheel and Axle WorksFigure 5

When a small input force isapplied to the wheel, thewheel rotates through acircular distance.

a

As the wheel turns, so doesthe axle. But because theaxle is smaller than thewheel, it rotates througha smaller distance, whichmakes the output forcelarger than the input force

b

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Wheels and Axles Brainstormwith students to generate a listof everyday objects that containwheels and axles. Write the liston the board, and then ask stu-dents to point out the wheeland the axle in each one.l Interpersonal

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Gears Set up a small gear sta-tion in the classroom. Obtainseveral gears of different sizes,a pegboard, and some pins tosecure the gears. Also, providestickers or pens to mark thegears. Explain that a gear is awheel with teeth around itsedge. Have students experimentwith the gears and try to calcu-late the mechanical advantageof a series of gears by using theequation for the wheel andaxle. l Kinesthetic


the radius of the wheel divided by the radiusof the axle.


3m 0.6m

MA � � 53 m0.6 m

Inclined PlanesDo you remember the story about how the Egyptians builtthe Great Pyramid? One of the machines they used was theinclined plane. An inclined plane is a simple machine that is astraight, slanted surface. A ramp is an inclined plane.

Using an inclined plane to load a piano into a truck, asFigure 7 shows, is easier than lifting the piano into the truck.Rolling the piano along an inclined plane requires a smallerinput force than is needed to lift the piano into the truck. Thesame work is done on the piano, just over a longer distance.

✓Reading Check What is an inclined plane?

Mechanical Advantage of Inclined PlanesThe greater the ratio of an inclined plane’s length to its heightis, the greater the mechanical advantage is. The mechanicaladvantage (MA) of an inclined plane can be calculated by divid-ing the length of the inclined plane by the height to which theload is lifted. The inclined plane in Figure 7 has a mechanicaladvantage of 3 m/0.6 m � 5.

inclined plane a simple machinethat is a straight, slanted surface,which facilitates the raising of loads;a ramp

Figure 7 The work you do onthe piano to roll it up the rampis the same as the work youwould do to lift it straight up. Aninclined plane simply allows youto apply a smaller force over agreater distance.

MA � lh

MA � � 44.8 m1.2 m

Mechanical Advantage of an Inclined Plane Aheavy box is pushed up a ramp that has anincline of 4.8 m long and 1.2 m high. Whatis the mechanical advantage of the ramp?

Step 1: Write the equation for the mechanicaladvantage of an inclined plane.

Step 2: Replace l and h with length andheight.

Now It’s Your Turn1. A wheelchair ramp is 9 m long and

1.5 m high. What is the mechanicaladvantage of the ramp?

2. As a pyramid is built, a stone block isdragged up a ramp that is 120 m longand 20 m high. What is the mechanicaladvantage of the ramp?

3. If an inclined plane were 2 m long and8 m high, what would be its mechanicaladvantage?


Inclined Planes Use Figure 7to explain how you can deter-mine mechanical advantage ofan inclined plane by using dis-tances. Explain the processas follows:

work input � work output

F (input) � d (input) �

F (output) � d (output)

This equation can be rearrangedinto ratios to show

F (input)�

d (output) F (output) d (input)

The force ratio can be used todetermine mechanical advan-tage. Because the distance ratiois equivalent to the force ratio,the distance ratio can also beused to determine mechanicaladvantage. l Visual


A slanted surface that makes theraising of loads easier, such as aramp.

Answers to Math Focus

1. MA � 9 m � 1.5 m � 62. MA � 120 m � 20 m � 63. MA � 2 m � 8 m � 0.25

SUPPORT FOR

English Language LearnersTypes of Machines Students will needadditional help processing all the infor-mation presented in this section. As theyread, ask them to fill in a table listing eachtype of machine and summarizing itsadvantages in their own words. Encouragestudents to sketch the machine and writethe mechanical advantage equation tohelp them remember it. Allow them to usedictionaries if needed for comprehension,but remind them the information in the

table should relate to the uses of wordsin the textbook. When students havefinished reading and their tables are com-plete, call on students to assist you in nar-rating a brief demonstration of each typeof machine, followed by an open discus-sion of its mechanical advantage. Encour-age full participation.l Verbal/Visual


MA � � 48 cm2 cm

8 cm

2 cm

Figure 8 A knife is a common example of a wedge, a simplemachine consisting of two inclined planes back to back.

wedge a simple machine that ismade up of two inclined planes andthat moves; often used for cutting

screw a simple machine that con-sists of an inclined plane wrappedaround a cylinder

Figure 9 If you couldunwind a screw, you wouldsee that it is actually a verylong inclined plane.

WedgesImagine trying to cut a melon in half with a spoon. It wouldn’tbe easy, would it? A knife is much more useful for cuttingbecause it is a wedge. A wedge is a pair of inclined planes thatmove. A wedge applies an output force that is greater thanyour input force, but you apply the input force over a greaterdistance. For example, a knife is a common wedge that caneasily cut into a melon and push apart its two halves, as shownin Figure 8. Other useful wedges include doorstops, plows, axheads, and chisels.

Mechanical Advantage of WedgesThe longer and thinner the wedge is, the greater its mechanicaladvantage is. That’s why axes and knives cut better when yousharpen them—you are making the wedge thinner. Therefore,less input force is required. The mechanical advantage of awedge can be found by dividing the length of the wedge byits greatest thickness, as shown in Figure 8.

ScrewsA screw is an inclined plane that is wrapped in a spiral arounda cylinder, as you can see in Figure 9. When a screw is turned, asmall force is applied over the long distance along the inclinedplane of the screw. Meanwhile, the screw applies a large forcethrough the short distance it is pushed. Screws are used mostcommonly as fasteners.

Mechanical Advantage of ScrewsIf you could unwind the inclined plane of a screw, you wouldsee that the plane is very long and has a gentle slope. Recallthat the longer an inclined plane is compared with its height,the greater its mechanical advantage. Similarly, the longer thespiral on a screw is and the closer together the threads are,the greater the screw’s mechanical advantage is. A jar lid is ascrew that has a large mechanical advantage.


Wedges Use Figure 8 to helpstudents understand that theoutput force from the wedge isapplied perpendicularly to theinput force. For instance, whenyou slide a doorstop under adoor (a horizontal input force),the wedge pushes up on thedoor (a vertical output force).l Visual

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PORTFOLIO

Screws To help stu-dents better understand

the concept of a screw, havethem make a screw by cuttingout the shape of an inclinedplane. Have them color the slop-ing edge of the plane with amarker. Then, have them wrapthe inclined plane around a pen-cil, starting with the tallest endof the plane. Point out that thecolored edge of the inclinedplane forms the thread of ascrew. l Kinesthetic

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

Mechanical Advantages ofScrews Provide three or fourscrews for each student. Havestudents calculate and comparethe mechanical advantage foreach screw by dividing thelength of the inclined planeby the height of the screw. Tomeasure the length of the screwthreads, students should wrap apiece of string around five turnsof the screw and then unwindand measure the string. Bycounting the total number ofscrew threads over the entirelength of the screw, they canestimate the total length. Thistotal length should be used forthe length of the inclined plane.To determine the height, stu-dents should measure the screwfrom the top screw thread tothe bottom. l Logical

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M A T E R I A L SFOR EACH PAIR• cardboard• magnifying lenses• zippers, new or old

Zippers Have pairs of students examinea zipper. Have them discuss how the slideon the zipper works and write two or threeparagraphs describing the parts of the slidein terms of simple machines. l Verbal

h-----------------------------a

The Archimedes Screw Have studentsresearch the invention of the Archimedesscrew and the screw’s use through the cen-turies up to the present day. Have themdescribe as many applications of the screwas they can. l Logical


Everyday MachinesWith an adult, think offive simple or compoundmachines that you encountereach day. List them in yourscience journal, andindicate what type ofmachine each is. Includeat least one compoundmachine and one machinethat is part of your body.

compound machinecompound machine a machinemade of more than one simplemachine

✓✓Reading Check

Wedge

Wheeland axle

Secondclass lever

Figure 10 A can opener is acompound machine. The handle is asecond-class lever, the knob is a wheeland axle, and a wedge is used toopen the can.

Compound MachinesYou are surrounded by machines. You even have machinesin your body! But most of the machines in your world arecompound machines,compound machines, machines that are made of two or moresimple machines. You have already seen one example of acompound machine: a block and tackle. A block and tackleconsists of two or more pulleys.

Figure 10 shows a common example of a compoundmachine. A can opener may seem simple, but it is actuallythree machines combined. It consists of a second-class lever, awheel and axle, and a wedge. When you squeeze the handle,you are making use of a second-class lever. The blade of thecan opener acts as a wedge as it cuts into the can’s top. Theknob that you turn to open the can is a wheel and axle.

Mechanical Efficiency of Compound MachinesThe mechanical efficiency of most compound machines islow. The efficiency is low because compound machines havemore moving parts than simple machines do, thus there ismore friction to overcome. Compound machines, such asautomobiles and airplanes, can involve many simple machines.It is very important to reduce friction as much as possible,because too much friction can damage the simple machinesthat make up the compound machine. Friction can be loweredby using lubrication and other techniques.

What special disadvantage do compoundmachines have?

Reteaching -------------------------------------bSimple Versus CompoundMachines Review the types ofsimple machines and the waysin which each changes size ordirection of force. Then, askstudents for examples of com-pound machines and the simplemachines that compose them.l Logical

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

1. Why are simple machines souseful? (They make work easier.)

2. Identify types of simplemachines you might find ona playground. Describe howeach of them modifies work.(Sample answer: seesaw: leverchanges direction of input force;merry-go-round: wheel and axlemakes the input force on the axlecause the wheel to move in acircle)

3. How does reducing frictionincrease the mechanical effi-ciency of a compound ma-chine? (Less work input is usedto overcome friction, so workoutput is higher, and mechanicalefficiency is higher.)

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

Machines in a Story Have eachstudent write a story that incor-porates six simple or compoundmachines. The machines mustoperate in some way appropriateto the story line. Suggest thatstudents illustrate theirstories. l Verbal


They have more moving parts than simplemachines do, so compound machines tend to beless efficient than simple machines are.



SummarySummary

Review

• In a first-class lever, the fulcrum is betweenthe force and the load. In a second-classlever, the load is between the force andthe fulcrum. In a third-class lever, the forceis between the fulcrum and the load.

• The mechanical advantage of an inclinedplane is length divided by height. Wedgesand screws are types of inclined planes.

• A wedge is a type of inclined plane. Itsmechanical advantage is its length dividedby its greatest thickness.

• The mechanical advantage of a wheel andaxle is the radius of the wheel divided bythe radius of the axle.

• Types of pulleys include fixed pulleys,movable pulleys, and block and tackles.

• Compound machines consist of two ormore simple machines.

• Compound machines have low mechani-cal efficiencies because they have moremoving parts and therefore more frictionto overcome.

Using Key Terms

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

2. Use the following terms in the same sentence:inclined plane, wedge, and screw.


3. Which class of lever always has a mechanicaladvantage of greater than 1?

a. first-classb. second-classc. third-classd. None of the above

4. Give an example of each of the followingsimple machines: first-class lever, second-classlever, third-class lever, inclined plane, wedge,and screw.

Math Skills

5. A ramp is 0.5 m high and has a slope that is 4 mlong. What is its mechanical advantage?

6. The radius of the wheel of a wheel and axleis 4 times the radius of the axle. What is themechanical advantage of the wheel and axle?

Critical Thinking

7. Applying Concepts A third-class lever has amechanical advantage of less than 1. Explainwhy it is useful for some tasks.

8. Making Inferences Which compoundmachine would you expect to have the lowestmechanical efficiency: a can opener or a pairof scissors? Explain your answer.

Interpreting Graphics

9. Indicate two simple machines being used inthe picture below.

Topic: Simple Machines;Compound Machines

SciLinks code: HSM1395; HSM0331


1. Sample answer: A lever is a sim-ple machine consisting of a barthat pivots at a fulcrum, acting tolift a load.

2. Sample answer: Wedges andscrews are two special types ofinclined planes.

3. b4. Sample answer: first-class lever:

seesaw; second-class lever:bottle opener; third-class lever:hammer; inclined plane: ramp;wedge: doorstop; screw: jar lid

5. MA � 4 m � 0.5 m � 86. MA � 4 � 1 � 47. A third-class lever increases the

distance through which force isoutput.

8. Sample answer: a can opener;It is a compound machine thatconsists of three simple machines,whereas a pair of scissors is acompound machine that consistsof two simple machines. Thefewer the number of simplemachines that make up a com-pound, the greater the mechanicalefficiency of the compoundmachine. A compound machineconsisting of few simple machineshas fewer moving parts.

9. The door on its hinge is a lever(second-class); the knob is awheel and axle.

CHAPTER RESOURCES


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


LabSkills PracticeUsing Scientifi c Methods

Calculate the work andpower used to climb afl ight of stairs.

Compare your work andpower with that of a 100 Wlight bulb.

• flight of stairs

• ruler, metric

• stopwatch

A Powerful WorkoutDoes the amount of work that you do depend on how fast youdo it? No! But the amount of time in which you do work doesaffect your power—the rate of work done. In this lab, you’llcalculate your work and power for climbing a flight of stairsat different speeds. Then you’ll compare your power with thatof an ordinary household object—a 100 W light bulb.

Ask a Question

1 How does your power in climbing a flight of stairs comparewith the power of a 100 W light bulb?

Form a Hypothesis

2 Write a hypothesis that answers the question in step 1. Explainyour reasoning.

Data Collection Table

Height ofstep (cm)

Numberof steps

Height ofstairs (m)

Time forslow walk (s)

Time forquick walk (s)

Test the Hypothesis

3 Copy the Data Collection Table onto a separate sheet ofpaper.

4 Use a metric ruler to measure the height of one stair step.Record the measurement in your Data Collection Table. Besure to include units for all measurements.

5 Count the number of stairs, including the top step, and recordthis number in your Data Collection Table.

6 Calculate the height of the climb by multiplying the number ofsteps by the height of one step. Record your answer in meters.(You will need to convert your answer from centimeters tometers.)

7 Use a stopwatch to measure how many seconds it takes youto walk slowly up a flight of stairs. Record your measurementin your Data Collection Table.

OBJECTIVES

MATERIALS

DO NOT WRITE IN BOOKNOT WRITE IN B

Skills PracticeSkills Practice LabLab

A Powerful Workout

Teacher’s Notes

Time RequiredOne or two 45-minute classperiods

Lab Ratings

rTeacher Prep f

Student Set-Up f

Concept Level ff

Clean Up f

M A T E R I A L SThe materials listed for this lab arefor the entire class or for smallergroups. Students in wheelchairs canuse a ramp instead of a flight ofstairs.

Safety CautionStudents who have asthma orany other respiratory problemsshould not perform this lab. Anystudent who becomes windedshould sit down and take deepbreaths. Caution students thatthis is not a race to see who canget the fastest time.

Answer

2. Sample answer: Climbingup a flight of stairs takes lessthan 100 W of power. Thisamount of energy doesn’t seemto be as much energy as a lightbulb gives off. Lab Notes

To help students calculate averages, set upa class data table on the board. The tableshould have four columns: “Student”;“Power S” (for power for slow walk);“Power Q” (for power for quick walk); and“Average” (each student’s average power).An individual’s average power is one-halfof the sum of the power for a slow walkand the power for a quick walk. The classaverage power is all the individual averagestogether divided by the number of studentsin the class.

CHAPTER RESOURCES


CRF • Datasheet for Chapter Lab• Lab Notes and Answers

Technology

Classroom Videos• Lab Video

• Inclined to Move• Wheeling and Dealing• Building Machines


8 Now measure how many seconds it takes youto walk quickly up a flight of stairs. Be carefulnot to overexert yourself. This is not a race tosee who can get the fastest time!

Analyze the Results

1 Constructing Tables Copy the CalculationsTable below onto a separate sheet of paper.

2 Examining Data Determine your weight innewtons, and record it in your CalculationsTable. Your weight in newtons is your weight inpounds (lb) multiplied by 4.45 N/lb.

3 Examining Data Calculate and record yourwork done in climbing the stairs by using thefollowing equation:

work � force � distance

(Hint: If you are having trouble determiningthe force exerted, remember that force is meas-ured in newtons.)

4 Examining Data Calculate and record yourpower output by using the following equation:

The unit for power is the watt (1 watt �

1 joule/second).

Draw Conclusions

5 Evaluating Methods In step 3 of “Analyzethe Results,” you were asked to calculate yourwork done in climbing the stairs. Why weren’tyou asked to calculate your work for each trial(slow walk and quick walk)?

6 Drawing Conclusions Look at your hypothe-sis. Was your hypothesis correct? Now that youhave measured your power, write a statementthat describes how your power compares withthat of a 100 W light bulb.

7 Applying Conclusions The work done tomove one electron in a light bulb is very small.Write down two reasons why the power usedis large. (Hint: How many electrons are in thefilament of a light bulb? How did you use morepower in trial 2?)

power � timework

Communicating Your DataYour teacher will provide a class data tableon the board. Add your average power to thetable. Then calculate the average power fromthe class data. How many students would ittake to create power equal to the power of a100 W bulb?

Calculations Table

Weight(N)

Work(J)

Power forslow walk

(W)

Power forquick walk

(W)

DO NOT WRITE IN BOOK

DO NOT WRITE IN BOOK

Analyze the Results

2. Sample answer: 100 lb �

4.45 N/lb � 445 N. 3. Sample answer: 445 N �

4 m � 1,780 J. 4. Sample answer:

1,780 J�10 s � 178 W;1,780 J�5 s � 356 W

Draw Conclusions

5. The work is the same nomatter how long it takes.

6. Sample answer: The poweroutput in both the slow andquick walks was greater thanthe power of a 100 W light bulb.The original hypothesis wasnot correct.

7. The power of a light bulb islarge because there is a hugenumber of electrons moving inthe filament and the electronsare moving back and forth veryquickly.

Communicating Your DataSample answer: The average powerfor the class was 250 W, so it wouldtake two and a half 100 W bulbs toequal the power of one student.

CHAPTER RESOURCESWorkbooks

Whiz-Bang Demonstrations• Pull-Ease, Please!b• A Clever Leverb

Inquiry Labs• Get an Arm and an Egg Upa

Long-Term Projects & Research Ideas• To Complicate Thingsa

Terry Rakes

Elmwood Junior HighRogers, Arkansas

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

Chapter 8 • Chapter Lab 231

For each pair of terms, explain how the meanings of the terms differ.

1 work and power

2 lever and inclined plane

3wheel and axle and pulley

Multiple Choice

4 Work is being done when

a. you apply a force to an object.b. an object is moving after you

applied a force to it.c. you exert a force that moves an

object in the direction of the force.d. you do something that is diffi cult.

5 What is the unit for work?

a. jouleb. joule per secondc. newtond. watt

6 Which of the following is a simple machine?

a. a bicycleb. a jar lidc. a pair of scissorsd. a can opener

7 A machine can increase

a. distance by decreasing force.b. force by decreasing distance.c. neither distance nor force.d. Either (a) or (b)

8 What is power?

a. the strength of someone or something

b. the force that is usedc. the work that is doned. the rate at which work is done

9 What is the unit for power?

a. newtonb. kilogramc. wattd. joule

Short Answer

0 Identify the two simple machines that make up a pair of scissors.

q Explain why you do work on a bag of groceries when you pick it up but not when you carry it.

w Why is the work output of a machine always less than the work input?

e What does the mechanical advantage of a fi rst-class lever depend upon? Describe how it can be changed.

Math Skills

r You and a friend together apply a force of 1,000 N to a car, which makes the car roll 10 m in 1 min and 40 s.

a. How much work did you and your friend do together?

b. What was the power output?

t A lever allows a 35 N load to be lifted with a force of 7 N. What is the mechanical advantage of the lever?

UNDERSTANDING KEY IDEAS

USING KEY TERMS


11. Sample answer: When you pick up a bag of groceries, the bag moves in the direction of the force. While you are holding the bag and walking, your forward motion is per-pendicular to the upward force you are using to carry the bag, so you are not doing work on the bag.

12. Friction involved in the operation of the machine’s moving parts causes some of the input energy to be lost as heat.

13. Sample answer: The mechanical advantage of a first-class lever depends upon the placement of the fulcrum. If the fulcrum is closer to the load than to the input force, the lever has a mechanical advantage of greater than 1. If the fulcrum is exactly in the middle of the load and the input force, the mechanical advantage of the lever is 1. If the fulcrum is closer to the input force than to the load, the lever has a mechanical advantage of less than 1.

14. a. W � 1,000 N � 10 m � 10,000 J b. P � 10,000 J � 100 s � 100 W15. MA � 35 N � 7 N � 5

ANSWERS

Using Key Terms1. Sample answer: Work is a

measure of the energy required to exert force over a distance. Power is a measure of the rate at which work is done.

2. Sample answer: A lever is a simple machine that consists of a bar that pivots on a ful-crum. An inclined plane is a simple machine that consists of a straight, slanted surface.

3. Sample answer: A wheel and axle is a simple machine that consists of two attached circular objects of different sizes. A pulley is a simple machine consisting of a grooved wheel that holds a rope or a cable.

Understanding Key Ideas4. c5. a6. b7. d8. d9. c

10. first-class levers and wedges

Assignment GuideSECTION QUESTIONS

1 1, 4–5, 8–9, 11,

2 7, 12, 15–16, 18, 20, 22

3 2–3, 6, 10, 13, 17, 19, 21, 23–24

s Identifying Relationships If the mechanical advantage of a certain machine is greater than 1, what does that tell you about the relation-ship between the input force and dis-tance and output force and distance?

For each of the images below, identify the class of lever used and calculate the mechanical advantage of the lever.

d

f

yConcept Mapping Use the following terms to create a concept map: work,force, distance, machine, and mechanicaladvantage.

uAnalyzing Ideas Explain why levers usually have a greater mechanical efficiency than other simple machines do.

iMaking Inferences The amount of work done on a machine is 300 J, and the machine does 50 J of work. What can you say about the amount of friction that the machine has while operating?

oApplying Concepts The winding road shown below is a series of inclined planes. Describe how a winding road makes it easier for vehicles to travel up a hill.

pPredicting Consequences Why wouldn’t you want to reduce the friction involved in using a winding road?

aMaking Comparisons How does the way that a wedge’s mechanical advantage is determined differ from the way that a screw’s mechanical advantage is determined?

force120 N

40 N

Input force20 N

force4 N

CRITICAL THINKING

INTERPRETING GRAPHICS

Critical Thinking16. An answer to this

exercise can befound at the endof this book.

17. Levers don’t have a lot of mov-ing parts, so they don’t gener-ate as much friction as othermachines do.

18. Sample answer: The work out-put of the machine is muchlower than the work input.Presumably, the machine oper-ates with a lot of friction.

19. It allows the work needed toclimb up the hill to be spreadout over a long distance,thereby requiring less force.

20. Sample answer: This is a casein which friction is useful. Itincreases the traction of thecars’ tires on the road andkeeps them from slipping asthey make turns. Reducing thefriction on the winding roadwould make the road moredangerous to drive on.

21. A wedge’s mechanical advan-tage is its length divided bygreatest width. A screw’smechanical advantage is deter-mined by comparing its spiralthread length with its verticallength.

22. The input force will be less thanthe output force, and the inputdistance will be greater thanthe output distance.

Interpreting Graphics23. second-class lever;

MA � 120 N � 40 N � 324. third-class lever;

MA � 4 N � 20 N � 0.2

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.

Chapter 8 • Chapter Review 233

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

Passage 1 The Great Pyramid, located in Giza, Egypt, covers an area the size of 7 city blocks and rises about 40 stories high. The Great Pyramid was built around 2600 BCE and took less than 30 years to complete. During this time, the Egyptians cut and moved more than 2 million stone blocks, most of which average 2,000 kg. The workers did not have cranes, bulldozers, or any other heavy-duty machines. What they did have were two simple machines—the inclined plane and the lever. Archeologists have found the remains of inclined planes, or ramps, made from mud, stone, and wood. The Egyptians pushed or pulled the blocks along ramps to raise the blocks to the proper height. Notches in many blocks indicate that huge levers were used as giant crowbars to lift and move the heavy blocks.

1. What is the main idea of the passage?

A Archeologists have found the remains of inclined planes near the pyramids.

B The Great Pyramid at Giza was built in less than 30 years.

C The Egyptians cut and moved more than 2 million stone blocks.

D The Egyptians used simple machines to build the Great Pyramid at Giza.

2. Which of the following is a fact stated in the passage?

F The Great Pyramid was made using more than 2 million stone blocks.

G Each of the stone blocks used to build the Great Pyramid was exactly 2,000 kg.

H Ancient Egyptians used cranes to build the Great Pyramid.

I The Great Pyramid at Giza has a mass of about 2 million kg.

Passage 2 While riding a bicycle, you have prob-ably experienced vibrations when the wheels of the bicycle hit bumps in the road. The force of the vibrations travels up through the frame to the rider. Slight vibrations can cause discomfort. Large ones can cause you to lose control of the bike and crash. Early bicycle designs made no attempt to dampen the shock of vibrations. Later designs used air-filled rubber tires and softer seats with springs to absorb some of the vibrations. Today’s bike designs provide a safer, more comfortable ride. Various new materials—titanium, for exam-ple—absorb shock better than traditional steel and aluminum do. More important, designers are putting a variety of shock absorbers—devices that absorb energy—into bike designs.

1. In the passage, what does the term shock mean?

A a medical emergency that can be caused by blood loss

B a dry material used in early bicyclesC a feeling of being stunned and surprisedD a jolt or impact

2. Which of the following is a fact stated in the passage?

F You have experienced vibrations while bicycle riding.

G Slight vibrations can cause severe discomfort.

H Titanium absorbs shock better than aluminum does.

I Today’s bike designs provide a more fashionable ride.


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 11. D2. F

Question 1: The information stated in answers A, B, and C is true, but those answers do not encompass the main idea of the passage as answer D does.

Passage 21. D2. H Question 1: A and C may be true alternative

definitions of the word shock, but D states the meaning of the word given in the passage. This question tests students’ ability to read for meaning in context.

READING

MISCONCEPTIONALERT

Stand

ardized

Test Prep

aration

1. How does this lever make work easier?

A by changing the direction of the forceB by increasing both force and distanceC by increasing force and decreasing distanceD by decreasing force and increasing distance

2. What would the mechanical advantage of this lever be?

F less than 1G 1H greater than 1I There is not enough information to

determine the answer.

3. What type of lever is the lever in the diagram?

A a first-class leverB a second-class leverC a third-class leverD There is not enough information to

determine the answer.

4. Which of the following items is the same type of lever as the lever in the diagram?

F a seesawG a wheelbarrowH a bottle openerI an arm lifting a barbell

1. For a special musical number during a school choir concert, 6 students stood in the first row, 10 students stood in the second row, and 14 students stood in the third row. If the pattern continued, how many students stood in the fifth row?

A 18B 22C 26D 30

2. Michael baked some bread for his friends. He put 2½ cups of flour in each loaf. He used a total of 12½ cups of flour. How many loaves did he make?

F 2 loavesG 4 loavesH 5 loavesI 15 loaves

3. A force of 15 N is exerted over a distance of 6 m. How much work was done? (Use the equation W � F � d.)

A 21 JB 21 NC 90 JD 90 N

4. If 350 J of work was done in 50 s, what was the power output? (Use the equation P � W/t.)

F 7 WG 70 WH 1,750 WI 17,500 W

Fulcrum

Load

Output forceInput force

Use the diagram below to answer the ques-tions that follow.

Read each question below, and choose the best answer.

INTERPRETING GRAPH ICS MATH INTERPRETING GRAPHICS1. D2. F3. C4. I

Question 1: The difference in sizesbetween the input force and outputforce arrows in the diagram indicatesthat the output force is smaller thanthe input force. This information aloneis enough to point to answer D. Youcan tell by the directions of the arrowsthat the direction of the force is notchanged.

MATH1. B2. H3. C4. F

Question 3: The unit of work andenergy is joules, so B and D can beruled out. A would be selected by astudent mistakenly adding force anddistance instead of multiplying them.

CHAPTER RESOURCES


CRF • Standardized Test Preparationg

State Resources

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

Chapter 8 • Standardized Test Preparation 235

Sciencein Action


in Action

MathA conveyor belt on a kinetic sculpture lifts a ball to a point 0.8 m high. It exerts 0.05 N of force as it does so. How much work does the conveyor belt do on the ball?

Language ArtsWrite a short story in which nanobots are used to save

someone’s life. Describe the machines the nanobots use in destroying deadly bacteria, clearing blood clots, or delivering medicine.

Science, Technology,

and SocietyKinetic SculptureThe collection of tubes, tracks, balls, and blocks of wood shown in the photo is an audio-kinetic sculpture. A conveyor belt lifts the balls to a point high on the track, and the balls wind their way down as they are pulled by the force of gravity and pushed by various other forces. They twist through spirals, drop straight down tubes, and some-times go up and around loops as if on a roller coaster. All this is made possible by the artist’s applications of principles of kinetic energy, the energy of motion.

The technology of making things smaller and smaller keeps growing and growing. Powerful computers can now be held in the palm of your hand. But what can motors that are smaller than grains of pepper do? How can gnat-sized robots that can swim through the bloodstream be used? One pos-sible field in which very small machines, nanomachines, can be used is in medicine.

Some scientists are looking into the pos-sibility of creating cell-sized machines called nanobots. These tiny robots may have many uses in medicine if they can be injected into a person’s bloodstream.

WRITINGSKILL

Science, Technology,

and Society

BackgroundThe kinetic sculpture pictured was built by Alexander Calder, who is best known for inventing the mobile. He died at the age of 78, after creating 16,000 works of art.

Weird Science

BackgroundAdvances in microtechnology have allowed scientists to achieve impressive results in many fields. For example, medi-cal researchers are working on special pills equipped with sen-sors, tiny pumps, and drug reservoirs.

Other technological advances include microscopic filters and air turbines for controlling the temperature of microchip arrays. One team of scientists has cre-ated a molecular “on-off switch” that could be used to store infor-mation in computers.

Answer to Math Activity

W � 0.05 N � 0.8 m � 0.04 JAnswer to Language Arts Activity

Encourage creativity and scientific accuracy by providing students with a body atlas or similar reference work. Suggest the idea of specialized nanobots who can travel through only certain systems of the body (such as the circulatory, endocrine, or nervous system). What common problems might occur in that environment, and what could they do to help? For example, a nanobot inside a lung would see bronchial tubes, alveoli, and capillaries. The nanobot could break down contaminants in the air sacs, help fight off infections, or remove fluids in patients who have pneumonia.

Chapter 8 • Science In Action 237

Social Studies

Mike HenslerThe Surf Chair Mike Hensler was a lifeguard at Daytona Beach, Florida, when he realized that it was next to impossible for someone in a wheelchair to come onto the beach. Although he had never invented a machine before, Hensler decided to build a wheelchair that could be driven across sand without getting stuck. He began spending many evenings in his driveway with a pile of lawn-chair parts, designing the chair by trial and error.

The result of Hensler’s efforts looks very different from a conventional wheelchair. With huge rubber wheels and a thick frame of white PVC pipe, the Surf Chair not only moves easily over sandy terrain but also is weather resistant and easy to clean. The new-est models of the Surf Chair come with optional attachments, such as a variety of umbrellas, detachable arm-rests and footrests, and even places to attach fishing rods.

To learn more about these Science in Action topics, visitgo.hrw.com and type in thekeyword HP5WRKF.

Check out Current Science®

articles related to this chapter by visiting go.hrw.com. Just type in the keyword HP5CS08.

List some simple and com-pound machines that are used as access devices for people who are disabled. Research how these machines came to be in common use.

People in Science

BackgroundIn designing the Surf Chair, Hensler purposely avoided mate-rials that would make the chair look cumbersome or clinical. Because the beach is a place to relax and have fun, Hensler designed his chair to blend easily into such an environ-ment. This fun and practical wheelchair is now available at many public beaches. Daytona Beach, for example, provides free use of the Surf Chair for people who need wheelchairs.

Teaching Strategy - GENERAL

Have students design a device to help people at home who are mobility impaired. You might want to give them a specific goal, such as designing a device to retrieve something from the refrigerator.

Answer to Social Studies Activity

Wheelchairs consist of two wheels and axles. Wheelchair access ramps are inclined planes. Elevators (used instead of stairs by people who use wheelchairs) usually involve pulleys.

Documents

Work, Machines, and Energy - · PDF fileUNIT TIMELINE 3 Work, Machines, and Energy Can you imagine living in a world with no machines? In this unit, you will explore the scientific