CHAPTER 1 The World of Physical Science · PDF fileNEW TERMS physical science OBJECTIVES! Describe physical science as the study of energy and matter.! Explain the role of physical

Would You Believe . . . ?In the fifteenth century, Leonardo da Vinci,a famous Italian artist and scientist, studiedsea gulls to try to learn the secrets of flight.Although he never built a successful flyingmachine, he did learn a lot about the sci-entific principles of flight. Many other scien-tists have been inspired by nature—includingJames Czarnowski (zahr NOW SKEE) andMichael Triantafyllou (tree AHN ti FEE loo),two scientists from the MassachusettsInstitute of Technology (MIT), in Cambridge.

In 1997, Czarnowski and Triantafyllouwere looking for an example from naturethat could inspire a new way to power boats.On a trip to the New England Aquarium, inBoston, Czarnowski was watching penguinsswim through the water when he realized

that the penguins couldbe nature’s answer. So heand Triantafyllou set out tocreate a boat that would imi-tate the way a penguin swims. After muchthought, many questions, and a lot of research,Proteus (PROH tee uhs)—the penguin boat—was born.

Less than 4 meters long, Proteus is pow-ered by two car batteries. Two broad paddles,similar to a penguin’s flippers, flap together

as often as 200 times per minute.At its top speed, this experimen-tal boat can “swim” through thewater at 2 meters per second. If afull-sized version of Proteus weredeveloped, it could cruise easily atabout 45 kilometers per hour. That’sfaster than most cargo carriers, whichmake up the majority of boats onthe ocean. Also, full-sized penguinboats would use less fuel, whichmeans that they would save moneyand produce less pollution.

Chapter 14

CH

AP

TE

R

1

Proteus (shown above on the Charles River) is namedafter the son of Poseidon, the Greek god of the sea.

The World ofPhysical Science

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

5

Mission Impossible?In this activity, you will do some creative thinkingto figure out a solution to what might seem likean impossible problem.

Procedure1. Examine an index card. Take note of its size

and shape. Your mission is to fit yourself throughthe card, as shown at right.

2. Brainstorm with a partner about possible waysto complete your mission, keeping the follow-ing guidelines in mind: You can use scissors,and you can fold the card, but you can-not use staples, paper clips, tape, glue,or any other form of adhesive.

3. When you and your partner have plannedyour strategy, write your procedure in yourScienceLog.

4. Test your strategy. Did it work? If necessary, getanother index card and try again, recording yournew strategy and results in your ScienceLog.

5. Share your strategies and results with othergroups in your class.

Proteus is acreative solution toa scientific problem.In this chapter, you’ll learnhow Czarnowski and Triantafyllouused a series of steps called thescientific method to develop thisamazing boat.

Analysis6. Why was it helpful to plan your strategy in

advance?

7. How did testing your strategy help you com-plete your mission?

8. How did sharing your ideas with your class-mates help you complete your mission? Whatdid they do differently?

In your ScienceLog, try to answer thefollowing questions based on what youalready know:

1. What is physical science?

2. What are some steps scientists taketo answer questions?

3. What purpose do models serve?


N E W T E R M Sphysical science

O B J E CT I V E S! Describe physical science as the

study of energy and matter.! Explain the role of physical sci-

ence in the world around you.! Name some careers that rely

on physical science.

Section1

6

Exploring Physical ScienceIt’s Monday morning. You’re eating breakfast and trying topull yourself out of an early morning daze. As you eat aspoonful of Crunch Blasters, your favorite cereal, you lookdown and notice your reflection in your spoon. Something’sfunny about it—it’s upside down! “Why is my reflectionupside down even though I’m holding the spoon right sideup?” you wonder. Is your spoon playing tricks on you? Next

you look at the back of the spoon. “A-ha!” youthink, “Now my reflection is right side up!”

However, when you look back at theinside of the spoon, your reflection

is upside down again. What is itabout the spoon that makes

your reflection look right sideup on one side and upsidedown on the other?

That’s Science!What would you say ifsomeone told you that youwere just doing science?

You may not realize it, butthat’s exactly what it was.

Science is all about being curi-ous, making observations, and

asking questions about those obser-vations. For example, you noticed

your reflection in your spoon and becamecurious about it. You observed that it was upside

down, but that when you looked at the back of the spoon,your reflection was right side up. Then you asked what thetwo sides of the spoon had to do with your reflection. Soyou were definitely doing science!

Everyday Science Science is all around you, even if you’renot thinking about it. Everyday actions such as putting on yoursunglasses when you’re outside, timing your microwave pop-corn just right, and using the brakes on your bicycle all useyour knowledge of science. But how do you know how to dothese things? From experience—you’ve gained an understand-ing of your world by observing and discovering all your life.

Because science is all around, you might not be surprisedto learn that there are different branches of science. This bookis all about physical science. So just what is physical science?

Chapter 1Copyright © by Holt, Rinehart and Winston. All rights reserved.

Matter + Energy !! Physical SciencePhysical science is the study of mat-ter and energy. Matter is the “stuff”that everything is made of—evenstuff that is so small you can’t seeit. Your shoes, your pencil, and eventhe air you breathe are made of mat-ter. And all of that matter has energy.Energy is easier to describe than toexplain. For example, energy is partlyresponsible for rainbows in the sky,but it isn’t the rainbow itself. Whenyou throw a ball, you give the ballenergy. Moving objects have energy,as you can see in Figure 1. Food alsohas energy. When you eat food, theenergy in the food is transferred toyou, and you can use that energy tocarry out your daily activities. Butenergy isn’t always associated withmotion or food. All matter hasenergy, even matter that isn’t mov-ing, like that shown in Figure 2.

As you explore physical science,you’ll learn more about the rela-tionship between matter and energyby answering questions such as thefollowing: Why does paper burn butgold does not? Why is it harder tothrow a bowling ball than a base-ball? How can water turn into steamand back to water? All of the answershave to do with matter and energy.And although it is difficult to talkabout matter without talking aboutenergy, sometimes it is useful tofocus on one or the other. That’s why physical science is often dividedinto two categories—chemistry andphysics.

The World of Physical Science 7

Figure 2 All matter has energy—even this monumental stone headthat is over 1.5 m tall!

Figure 1 The cheetah, the fastest land mammal, has a lot ofenergy when running full speed. The cheetah also uses a lotof energy to run so fast. But a successful hunt will supply theenergy the cheetah needs to continue living.

!


Chemistry Studying all forms of matter and how they inter-act is what chemistry is all about. You’ll learn about theproperties and structure of matter and how different substances

behave under certain conditions, such as high tempera-ture and high pressure. You’ll also discover how and

why matter can go through changes, such as the oneshown in Figure 3. Check out the chart below tofind out what you can learn by studying chemistry.

Physics Like chemistry, physics deals with mat-ter. But unlike chemistry, physics is mostly con-cerned with energy and how it affects matter.Studying different forms of energy is whatphysics is all about. When you study physics,you’ll discover how energy can make matter dosome interesting things, as shown in Figure 4.You’ll also begin to understand aspects of yourworld such as motion, force, gravity, electricity,light, and heat. Check out the chart below tofind out what you can learn by studying physics.

Chapter 18

List three items in your class-room that you think resultedfrom advances in chemistry,and list three items that youthink resulted from advancesin physics. Compare the twolists. What do the items onthe two lists have in com-mon? Explain why. Compareyour lists with lists made byyour classmates.

By studying chemistry, you can find out . . .

! why yeast makes breaddough rise before you put itin the oven.

! how the elements chlorineand sodium combine to formtable salt, a compound.

! why water boils at 100°C.

! why sugar dissolves faster inhot tea than in iced tea.

! how pollution affects ouratmosphere.

By studying physics, you can find out . . .

! why you move to the rightwhen the car you’re in turnsleft.

! why you would weigh less onthe moon than you do onEarth.

! why you see a rainbow aftera rainstorm.

! how a compass works.

! how your bicycle’s gears helpyou pedal faster or slower.

Figure 4 When you study physics you’lllearn how energy causes the motion thatmakes a roller coaster ride so exciting.

Figure 3 When you wash your clothes, the detergent and the stains interact. The result? Clean clothes!


Physical Science Is All Around YouBelieve it or not, the things that you’ll learn about matter andenergy by studying physical science are important for whatyou’ll learn in other science classes, too. Take a look belowto see the role of physical science in areas that you mighthave thought only involved Earth science or life science.


Ecology uses physical science toexplain the nitrogen cycle andthe transfer of energy between organisms in a food chain.

Astronomy uses physical science to explain the composition ofplanets, the light given offby stars, and the motion ofdifferent galaxies in the universe.

Meteorology applies physical sciencein its study of the movement of airmasses, weather patterns, and thecomposition of the atmosphere.

Geology uses physical scienceto explain earthquake wavesand rock composition.

Botany, the study of plants, usesphysical science to explain howplants use carbon dioxide andwater to make food.

Oceanography uses physicalscience to explain waves,currents, and the chemistryof ocean water.

Biology uses physical scienceto explain how the heartpumps blood, how the eyesand ears work, and how thebrain sends electrical impulsesthroughout the body.


Physical Science in Action Now that you know physical science is all around you, youmay not be surprised to learn that a lot of careers rely onphysical science. What’s more, you don’t have to be a scien-tist to use physical science in your job! On this page, you cansee some career opportunities that involve physical science.

1. What is physical science all about?

2. List three things you do every day that use your experi-ence with physical science.

3. Applying Concepts Choose one of the careers listed inthe chart at left. How do you think physical science isinvolved in that career?

Chapter 110

REVIEWOther Careers Involving Physical Science

ArchitectPharmacistFirefighterEngineerConstruction workerOpticianPilotElectricianComputer technician

Gene Webb is an auto mechanic.He understands how the parts ofa car engine move and how tokeep cars working efficiently.

Sung Park is a photojournalist.He knows how to use differentamounts of light to ensure that his photographs capturethe best story.

Shirley Ann Jackson has used physical science as a researcher inthe semiconductor and opticalphysics industries. Former chair ofthe Nuclear Regulatory Commission,she became president of RensselaerPolytechnic Institute in 1999.

Julie Fields is a chemist whostudies the structures ofchemical substances foundin living organisms. Sheinvestigates how these sub-stances can be made in thelaboratory and turned intoproducts such as medicines.

Roberto Santibanez is a chef. Heknows how ingredients interactand how energy can cause thechemical changes that producehis delicious meals.


N E W T E R M Sscientific method datatechnology theoryobservation lawhypothesis

O B J E CT I V E S! Identify the steps used in the

scientific method.! Give examples of technology.! Explain how the scientific

method is used to answer ques-tions and solve problems.

! Describe how our knowledge ofscience changes over time.

Section2 Using the Scientific Method

When you hear or read about advancements in science, doyou wonder how they were made? How did the scientists maketheir discoveries? Were they just lucky? Maybe, but chancesare that it was much more than luck. The scientific methodprobably had a lot to do with it!

What Is the Scientific Method?The scientific method is a series of steps that scientists use toanswer questions and solve problems. The chart below showsthe steps that are commonly used in the scientific method.Although the scientific method has several distinct steps, it isnot a rigid procedure whose steps must be followed in a certainorder. Scientists may use the steps in a different order, skip steps,

or repeat steps. It all dependson what works best to answerthe question.

Do you remember JamesCzarnowski and MichaelTriantafyllou, the two scien-tists discussed at the begin-ning of this chapter? Whatscientific problem were theytrying to solve? In the nextfew pages, you’ll learn howthey used the scientificmethod to develop new technology—Proteus, the pen-guin boat.

Technology is the application of knowledge, tools, and materials to solve problems and accomplish tasks. Technology can also refer to the objects used to accomplish tasks. For example,computers, headphones, and the Internet are allexamples of technology. But even things liketoothbrushes, light bulbs, and pencils areexamples of technology. A toothbrushhelps you accomplish the task of clean-ing your teeth. A light bulb solves theproblem of how to read when thesun goes down. A pencil helps youaccomplish the task of writing.

Spotlight on Technology

11

Scienceand technology

are not the same thing.The goal of science is to

gain knowledge about thenatural world. The goal of tech-

nology is to apply scientificunderstanding to solve prob-

lems. Technology is some-times called applied

science.

The World of Physical Science

The Scientific Method

Ask a question.

Form a hypothesis.

Test the hypothesis.

Analyze the results.

Draw conclusions.

Communicate results.


Ask a Question Asking questions helps you focus your inves-tigation. A question identifies something you don’t know butwant to find out. Usually, scientists ask a question after they’vemade a lot of observations. An observation is any use of thesenses to gather information. Measurements are observationsthat are made with instruments, such as those shown in Figure 5. The chart below gives you some examples of obser-vations. Keep in mind that you can make observations at anypoint while using the scientific method.

So what question did the scientists who made Proteus ask?Czarnowski and Triantafyllou, shown in Figure 6, are engineers(EN juh NIRZ), scientists who put scientific knowledge to workfor practical human uses. Engineers create technology. Whilea graduate student in the department of Ocean Engineeringat the Massachusetts Institute of Technology, Czarnowskiworked with Triantafyllou, his professor, on improving boattechnology. Specifically, they wanted to observe boat propul-sion systems and investigate how to make them work better.

A propulsion system is what makes a boatmove; most boats are driven by propellers.

One thing that Czarnowski andTriantafyllou were studying is the efficiencyof boat propulsion systems. Efficiency com-pares energy output (the energy used tomove the boat forward) with energy input(the energy supplied by the boat’s engine).Czarnowski and Triantafyllou learned fromtheir observations that boat propellers,shown in Figure 7 on the next page, arenot very efficient.

Figure 6 James Czarnowski (left) and MichaelTriantafyllou (right) made observations abouthow boats work in order to develop Proteus.

12 Chapter 1

Figure 5Stopwatches and rulers are some of the manytools used to makeobservations.

Examples of Observations

! The sky is blue.

! The ice began to melt 30 sec-onds after it was taken out ofthe freezer.

! This soda bottle has a volumeof 1 liter.

! Cotton balls feel soft.

! The box was easier to movewhen I put it on wheels.

! He is 125 centimeters tall.

! Adding food coloring turnedthe water red. Adding bleachmade the water clear again.

! This brick feels heavier thanthis sponge.

! Sandpaper is rough.

! My dog responded to thewhistle, but I couldn’t hear it.


Why is boat efficiency important? Most boats are only about70 percent efficient. Making only a small fraction of the UnitedStates’ boats and ships just 10 percent more efficient wouldsave millions of liters of fuel per year. Saving fuel means sav-ing money, but it also means using less of the Earth’s supplyof fossil fuels. Based on their observations and all of this infor-mation, Czarnowski and Triantafyllou knew what they wantedto find out.

Propellers require a lot ofenergy to rotate, and someof that energy gets wastedin churning up the water.Only 70 percent of theenergy put into a propellersystem actually works tomove the boat forward.

Efficiency =

Efficiency is usually expressed as a percent-age. If much more energy is put into a sys-tem than the system puts out, then thesystem is not very efficient, and the percentefficiency will be low.

output energy!!input energy

The Question:How can boat propulsion systems be made more efficient?


Figure 7 Observations About the Efficiency of Boat Propellers

Propellers are rotated bymotors. As the propellers whirlaround, they push against thewater. As the water pushesback, the boat moves forward.

Ask some questions of yourown on page 516 in the

LabBook.

a

b

c


Form a Hypothesis Once you’ve asked your question, yournext step is forming a hypothesis. A hypothesis is a possibleexplanation or answer to a question. You can use what youalready know and any observations that you have made toform a hypothesis. A good hypothesis is testable. If no obser-vations or information can be gathered or if no experimentcan be designed to test the hypothesis, it is untestable.

In thinking of possible answers to their question,Czarnowski and Triantafyllou used their knowledge from

past boat projects. They were also looking for an exam-ple from nature on which to base their hypothesis.Czarnowski had made observations of penguinsswimming at the New England Aquarium. Figure 8shows how penguins propel themselves. He observedhow quickly and easily the penguins moved throughthe water. He also observed that penguins have a

rigid body, similar to a boat. These observa-tions led Czarnowski to wonder if penguins

could provide an answer to his question.Using their past experience and new

observations of penguins, the two sci-entists came up with a possible answerto their question: a propulsion systemthat works the way a penguin swims!

Before scientists test a hypothesis, they often make pre-dictions that state what they think will happen during theactual test of the hypothesis. Scientists usually state predic-tions in an “If . . . then . . .” format. The engineers at MITmight have made the following prediction: If two flippers are attached to a boat, then the boat will be more efficientthan a boat powered by propellers.

1. How do scientists and engineers use the scientific method?

2. Give three examples of technology from your everyday life.

3. Analyzing Methods Explain how the accuracy of yourobservations might affect how you develop a hypothesis.

Chapter 114

REVIEW

life scienceC O N N E C T I O N

Penguins, although flightless,are better adapted to waterand extreme cold than anyother bird. Most of the world’s18 penguin species live andbreed on islands in the sub-antarctic waters. Penguins canswim as fast as 40 km/h, andsome can leap more than 2 mabove the water.

Hypothesis:A propulsion system that mimics the way a penguinswims will be more efficient than propulsion systems thatuse propellers.

Figure 8 Penguins use their flippers almost like wings to “fly” under-water. As they pull theirflippers toward theirbody, they push againstthe water, which propelsthem forward.


Test the Hypothesis After you form a hypothesis, you musttest it to determine whether it is a reasonable answer to yourquestion. In other words, testing helps you find out if yourhypothesis is pointing you in the right direction or if it is wayoff the mark. Often a scientist will test a hypothesis by test-ing a prediction.

One way to test a hypothesis is to conduct a controlledexperiment. In a controlled experiment, there is a control groupand an experimental group. Both groups are the same exceptfor one factor in the experimental group, called a variable. Theexperiment will then determine the effect that this variablehas on the system.

Sometimes a controlled experiment is not possible. Stars,for example, are too far away to be used in an experiment. Insuch cases, you can test your hypothesis by making additionalobservations or by conducting research. If your scientific inves-tigation involves creating technology to solve a problem, youtest your hypothesis in a different way. You make or buildwhat you want to test and see if it does what you expected itto do. That’s just what Czarnowski and Triantafyllou did—theybuilt Proteus, the penguin boat, shown in Figure 9.

Figure 9 Testing Penguin Propulsion

Proteus is only 3.4 m longand 50 cm wide, too narrowfor even a single passenger.

Proteus has two flipper-like paddles, calledfoils. Both foils moveout and then in, muchas a penguin uses itsflippers underwater.

A desktop computerprograms the numberof times the foils flapper second.

Each of Proteus’s flappingfoils is driven by a motorthat gets its energy fromtwo car batteries.

As the foils flap, they pushwater backward. The waterpushes against the foils,propelling the boat forward.


That’s Swingin’!1. Make a pendulum

by tying a piece ofstring to a ringstand and hanging a smallmass, such as a washer,from the end of the string.

2. Form a hypothesis aboutwhich factors (such aslength of string, mass, etc.)affect the rate at which thependulum swings.

3. In your ScienceLog, recordwhat factors you will con-trol and what factor will beyour variable.

4. Test your hypothesis byconducting several trials,recording the number ofswings made in a giventime, such as 10 seconds,for each trial.

5. Was your hypothesis sup-ported? In your ScienceLog,analyze your results.

e

a

b

c

d


Once constructed, Proteus was ready to test. After a few tri-als in a laboratory tank, Czarnowski and Triantafyllou tookProteus out into the open water of the Charles River. They wereready to collect data. Data are any pieces of information acquiredthrough experimentation. The engineers used an onboard com-puter to adjust the flapping motion and to measure how muchenergy the motors used. These measurements were data for theenergy input. The engineers did several tests, each time chang-ing only the flapping rate. For each test, data such as the flap-ping rate, energy used, and the speed achieved by the boatwere carefully recorded. The output energy was determined fromthe speed Proteus achieved.

Analyze the Results After you collect and record your dataand other observations, you must analyze them to determinewhether the results of your test support the hypothesis. To dothis, you must organize and study your data and observations.Sometimes doing calculations can help you learn more aboutyour results. Organizing numerical data into tables and graphsmakes relationships between information easier to see.

To analyze their results, Czarnowski and Triantafyllou usedthe data for energy input and energy output to calculateProteus’s efficiency for different flapping rates. These data canbe graphed as shown in the line graph in Figure 10. Rememberthat their hypothesis was that penguin propulsion would bemore efficient than propeller propulsion. The scientists com-pared Proteus’s highest level of efficiency—the efficiency at 1.7 flaps per second—with the average efficiency of a propeller-driven boat. Look at the bar graph in Figure 10 to see if theirdata support their hypothesis.

This bar graph shows that Proteusis 17 percent more efficient than a propeller-driven boat.

This line graph shows that Proteus was mostefficient when its foils were flapping about 1.7 times per second.

Chapter 116

Self-CheckWhat variable wereCzarnowski andTriantafyllou testing?(See page 596 to checkyour answer. )

Figure 10 Graphs of the Test Results

!

Flaps per second

Effic

ienc

y

0.7 1.2 1.7 2.2

70%

87%

Propeller-driven boat

Proteus


Draw Conclusions At the end of an investigation, you mustdraw a conclusion. You could conclude that your results sup-ported your hypothesis, that your results did not support yourhypothesis, or that you need more information. If your resultssupport your hypothesis, you can ask further questions. If yourresults do not support your hypothesis, you should check yourresults or calculations for errors. You may have to modify yourhypothesis or form a newone and conduct anotherinvestigation. If you findthat your results neithersupport nor disprove yourhypothesis, you may needto gather more information,test your hypothesis again,or redesign the procedure.

After Czarnowski andTriantafyllou analyzed theresults of their test, theyconducted many more tri-als. Still they found that thepenguin propulsion systemwas more efficient than apropeller propulsion sys-tem. So they concluded thattheir hypothesis was sup-ported, which led to morequestions, as you can see inFigure 11.

Communicate Results One of the most important steps inany investigation is to communicate your results. You canwrite a scientific paper explaining your results, make a pre-sentation, or create a Web site. Telling others what you learnedis how science keeps going. After you’ve completed an inves-tigation, other scientists can conduct their own tests, modifyyour tests to learn something more specific, or study a newproblem based on your results.

Czarnowski and Triantafyllou published their results inacademic papers, but they also displayed their project and itsresults on the Internet. In addition, science magazines andnewspapers have reported the work of these engineers. Thesereports allow you to conduct some research of your ownabout Proteus.


Figure 11 Could a penguin propulsion system be used on largeships, such as an oil tanker? Other scientists are conducting moreresearch to find out!


Breaking the Mold of the Scientific Method Not all sci-entists use the same scientific method, nor do they always fol-low the same steps in the same order. Why not? Sometimesyou may have a clear idea about the question you want toanswer. Other times, you may have to revise your hypothesisand test it again. While you should always take accurate meas-urements and record data correctly, you don’t always have tofollow the scientific method in a certain order. Figure 12 showsyou some other paths through the scientific method.

Building Scientific KnowledgeUsing the scientific method is a way to find answers to ques-tions and solutions to problems. But you should understandthat answers are very rarely final answers. As our understand-ing of science grows, our understanding of the world aroundus changes. New ideas and new experiments teach us newthings. Sometimes, however, an idea is supported again andagain by many experiments and tests. When this happens, theidea can become a theory or even a law. As you will read onthe next page, theories and laws help to build new scientificknowledge.

Chapter 118

No

Yes

Draw Conclusions

Do they support your hypothesis?

MakeObservations Form a

Hypothesis

Test YourHypothesis

Analyzethe Results

Ask a Question

Communicatethe Results

Turn to page 33 to discover a tale of young Einstein’s

encounter with some otherscience heavyweights.

Figure 12 Scientific investiga-tions do not always proceed fromone step of the scientific methodto the next. Sometimes steps areskipped, and sometimes they arerepeated.


Scientific Theories You’ve probably heard a detectiveon a TV show say, “I’ve got a theory about who com-mitted the crime.” Does the detective have a scientifictheory? Probably not; it might be just a guess. A sci-entific theory is more complex than a simple guess.

In science, a theory is a unifying explanation fora broad range of hypotheses and observations thathave been supported by testing. A theory not onlycan explain an observation you’ve made but also canpredict an observation you might make in the future.Keep in mind that theories, like the one shown in Figure 13, can be changed or replaced as new observationsare made or as new hypotheses are tested.

Scientific Laws What do you think of when you hear theword law? Traffic laws? Federal laws? Well, scientific laws arenot like these laws. Scientific laws are determined by nature,and you can’t break a scientific law!

In science, a law is a summary of many experimental resultsand observations. A law tells you how things work. Laws arenot the same as theories because laws only tell you what hap-pens, not why it happens, as shown in Figure 14. Although alaw does not explain why something happens, the law tellsyou that you can expect the same thing to happen every time.

1. Name the steps that can be used in the scientific method.

2. How is a theory different from a hypothesis?

3. Analyzing Ideas Describe how our knowledge of sciencechanges over time.


Figure 14 Dropping a ball illustrates thelaw of conservation of energy. Although theball doesn’t bounce back to its originalheight, energy is not lost—it is transferredto the ground.

REVIEW

WPS-P01-029-P

Figure 13 According to the big-bang theory, the universe wasonce a small, hot, and dense vol-ume of matter. About 10 to 20billion years ago, an event calledthe big bang sent matter in alldirections, forming the galaxiesand planets.


Chapter 120

N E W T E R M Smodel

O B J E CT I V E S! Explain how models represent

real objects or systems.! Give examples of different ways

models are used in science.

Section3 Using Models in

Physical ScienceThink again about Proteus. How much like a penguin was it?Well, Proteus didn’t have feathers and wasn’t a living thing,but its “flippers” were designed to create the same kind ofmotion as a penguin’s flippers. The MIT engineers built Proteusto mimic the way a penguin swims so that they could gain agreater understanding about boat propulsion. In other words,they created a model.

What Is a Model?A model is a representation of an object or system. Models areused in science to describe or explain certain characteristics ofthings. Models can also be used for making predictions andexplaining observations. A model is never exactly like the realobject or system—if it were, it would no longer be a model.Models are particularly useful in physical science because manycharacteristics of matter and energy can be either hard to seeor difficult to understand. You can see some examples of sci-entific models below.

Examples of Models

A cell diagram is amodel that lets youlook at all the parts ofa cell up close—withoutusing a microscope.

A model of a building can be designed on acomputer before moneyis spent constructingthe actual building.

A model rocket is muchsmaller than a real rocket,but launching one in yourbackyard can help youunderstand how real rock-ets blast off into space.

You can’t see the tinyparts that make up matter, but you canmake a model thatshows how the parts fit together.


Models Help You Visualize InformationWhen you’re trying to learn about something that you can’tsee or observe directly, a model can help you visualize it, orpicture it in your mind. Familiar objects or ideas can help youunderstand something a little less familiar.

Objects as Models When you use a realobject as a model for something you cannotsee, the object must have characteristics sim-ilar to those of the real thing. For example,a coiled spring toy is often used as a modelof sound waves. You’ve probably used thiskind of spring toy before, so it’s a familiarobject. Sound waves are probably a little lessfamiliar—after all, you can’t see them. Butthe spring toy behaves a lot like sound wavesdo. So using the spring toy as a model, asshown in Figure 15, can make the behaviorof sound waves easier to understand.

Ideas as Models When you’re trying tounderstand something but don’t have anobject to use as a model, you can create amodel from an idea. For example, when sugardissolves in iced tea, it seems to disappear. Totry to understand where the sugar went, imag-ine a single drop of tea magnified until it isalmost as big as you are, with tiny spacesbetween the particles of water in the tea.Using this model, as shown in Figure 16, youcan understand that the sugar seems to dis-appear because the sugar particles fit intospaces between the water particles in the tea.


You’ve probably seen a weather report on television.Think about the models that a weather reporter uses

to tell you about the weather: satellite pictures, color-codedmaps, and live radar images. How are these models usedto represent the weather? Why do you think that some-times weather forecasts are wrong?

Figure 15 A coiled spring toy can show youhow air particles crowd together in parts ofa sound wave.

Figure 16 Just by imagining a big drop oftea, you are creating a model!


Models Are Just the Right SizeHow can you observe how the phases of the moon occur?That’s a tough problem, because you’re on Earth and you can’teasily get off of the Earth to observe the moon going aroundit. But you can observe a model of the moon, Earth, and sun,as shown in Figure 17. As you can see, models can representthings that are too large to easily observe.

Models are also useful for under-standing things that are too small to

see. For example, you can tell just bylooking that a grain of salt has a defi-

nite shape, but you may not know why. Amodel of the structure of salt, as shown in

Figure 18, can help you understand how thearrangement of tiny particles accounts for its shape.

Models Build Scientific KnowledgeModels not only can represent scientific ideas and objects butalso can be tools that you can use to conduct investigationsand illustrate theories.

Testing Hypotheses The MIT engineers were trying to testtheir hypothesis that a boat that mimics the way a penguinswims would be more efficient than a boat powered by pro-pellers. How did they test this hypothesis? By building a model,Proteus. When using the scientific method to develop newtechnology, testing a hypothesis often requires building amodel. By conducting tests with Proteus, the MIT engineerstested their hypothesis and found out what factors affectedthe model’s efficiency. Using the data they collected, theycould consider building a full-sized penguin boat.

Chapter 122

Figure 17 Using this model, you can seehow the Earth’s rotation, in addition to themoon’s revolution around the Earth as theEarth revolves around the sun, results inthe different phases of the moon.

Build a model car and test itsspeed on page 517 in the

LabBook.

Figure 18 The particles of matter in a grain of salt connect in a continuous pattern that forms a cube. That’s why a grain of salt has a cubic shape.


Illustrating Theories Recall that a theory explainswhy things happen the way they do. Sometimes,however, a theory is hard to picture. That’s wheremodels come in handy. A model is different froma theory, but a model can present a picture of whatthe theory explains when you cannot actually observeit. You can see an example of this in Figure 19.

Models Can Save Time and MoneyWhen creating technology, scientists often create a model firstso that they can test its characteristics and improve its designbefore building the real thing. You may recall that Proteus wasn’tbig enough to carry even a single passenger. Why didn’t theMIT engineers begin by building a full-sized boat? Imagine ifthey had gone to all that trouble and found out that theirdesign didn’t work. What a waste! Models allow you to testideas without having to spend the time and money necessaryto make the real thing. In Figure 20, you can see another exam-ple of how models save time and money.

1. What is the purpose of a model?

2. Give three examples of models that you see every day.

3. Interpreting Models Both a globe and a flat world mapmodel certain features of the Earth. Give an example ofwhen you would use a globe and an example of whenyou would use a flat map.

Figure 20 Car engineers canconduct cyber-crashes, in whichcomputer-simulated cars crashin various ways. Engineers usethe results to determine whichsafety features to install on thecar—all without damaging a single automobile.


REVIEW

Figure 19 This model illustratesthe atomic theory, which statesthat all matter is made of tinyparticles called atoms.


Chapter 124

N E W T E R M Smeter temperaturevolume areamass density

O B J E CT I V E S! Explain the importance of the

International System of Units.! Determine the appropriate

units to use for particular measurements.

! Describe how area and densityare derived quantities.

Section4 Measurement and Safety in

Physical ScienceHundreds of years ago, different countries used different sys-tems of measurement. In England, the standard for an inchused to be three grains of barley placed end to end. Otherstandardized units of the modern English system, which isused in the United States, used to be based on parts of thebody, such as the foot. Such units were not very accuratebecause they were based on objects that varied in size.

Eventually people recognized that there was a need for asingle measurement system that was simple and accurate. Inthe late 1700s, the French Academy of Sciences began todevelop a global measurement system, now known as theInternational System of Units, or SI.

The International System of UnitsToday most scientists in almost all countries use the InternationalSystem of Units. One advantage of using SI measurements isthat it helps scientists share and compare their observations andresults. Another advantage of SI is that all units are based onthe number 10, which makes conversions from one unit toanother easy to do. The table in Figure 21 contains the com-monly used SI units for length, volume, mass, and temperature.

Common SI Units

Figure 21 Prefixes are usedwith SI units to convert themto larger or smaller units. Forexample kilo means 1,000times, and milli indicates1/1,000 times. The prefix useddepends on the size of theobject being measured.

Length

Volume

Mass

Temperature

meter (m)kilometer (km)decimeter (dm)centimeter (cm)millimeter (mm)micrometer (µm)nanometer (nm)

cubic meter (m3)cubic centimeter (cm3)liter (L)milliliter (mL)

kilogram (kg)gram (g)milligram (mg)

Kelvin (K)Celsius (!C)

1 km " 1,000 m1 dm " 0.1 m1 cm " 0.01 m1 mm " 0.001 m1 µm " 0.000001 m1 nm " 0.000000001 m

1 cm3 " 0.000001 m3

1 L " 1 dm3 " 0.001 m3

1 mL " 0.001 L " 1 cm3

1 g " 0.001 kg1 mg " 0.000001 kg

0!C " 273 K100!C " 373 K


Length How long is the construction crane shown in Figure 22?To describe its length, a physical scientist would use meters(m), the basic SI unit of length. Other SI units of length arelarger or smaller than the meter by multiples of 10. For exam-ple, 1 kilometer (km) equals 1,000 meters. One meter equals100 centimeters, or 1,000 millimeters. If you divide 1 m into1,000 parts, each part equals 1 mm. This means that 1 mm isone-thousandth of a meter. Although that seems pretty small,some objects are so tiny that even smaller units must be used.To describe the length of a grain of salt, micrometers (!m) ornanometers (nm) are used.

Volume Imagine that you need to move some lenses to alaser laboratory. How many lenses will fit into a crate? Thatdepends on the volume of the crate and the volume of eachlens. Volume is the amount of space that something occupiesor, as in the case of the crate, the amount of space that some-thing contains.

Volumes of liquids are expressed in liters (L). Liters arebased on the meter. A cubic meter (1 m3) is equal to 1,000 L.So 1,000 L will fit into a box 1 m on each side. A milliliter(mL) will fit into a box 1 cm on each side. So 1 mL = 1 cm3.Graduated cylinders are used to measure the volume of liquids.

Volumes of solid objects are expressed with cubic meters (m3).Volumes of smaller objects can be expressed with cubic cen-timeters (cm3) or cubic millimeters (mm3). To find the volumeof a crate, or any other rectangular shape, multiply the lengthby the width by the height. To find the volume of an irregu-larly shaped object, measure how much liquid that object dis-places. You can see how this works in Figure 23.

Figure 23 This graduated cylinder contains 70 mL of water. Afterthe rock is added, the water level moves to 80 mL. Because therock displaces 10 mL of water, and because 1 mL = 1 cm3, thevolume of the rock is 10 cm3.


Pick an object to use as aunit of measure. It could be apencil, your hand, or anythingelse. Find how many unitswide your desk is, and com-pare your measurement withthose of your classmates.What were some of the unitsthat your classmates used? Inyour ScienceLog, explain whyit is important to use stan-dard units of measure.

Figure 22 The length of thiscrane would be expressed inmeters.

a b

70 mL 80 mL


Mass How many cars can a bridge support? That depends onthe strength of the bridge and the mass of the cars. Mass isthe amount of matter that something is made of. The kilo-gram (kg) is the basic SI unit for mass and would be used toexpress the mass of a car. Grams (one-thousandth of a kilo-

gram) are used to express the mass of smallobjects. A medium-sized apple has a massof about 100 g. Masses of very large objectsare expressed in metric tons. A metric tonequals 1,000 kg.

Temperature How hot is melted iron? Toanswer this question, a physical scientistwould measure the temperature of the liq-uid metal. Temperature is a measure of howhot (or cold) something is. You are prob-ably used to expressing temperature withdegrees Fahrenheit (!F). Scientists often usedegrees Celsius (!C), but the kelvin (K) is theSI unit for temperature. The thermometer inFigure 24 compares !F with !C, the unit youwill most often see in this book.

Derived QuantitiesSome quantities are formed from combinations of other meas-urements. Such quantities are called derived quantities. Botharea and density are derived quantities.

Area How much carpet would it take to cover the floor of yourclassroom? Answering this question involves finding the area ofthe floor. Area is a measure of how much surface an object has.To calculate the area of a rectangular surface, first measure thelength and width, then use the following equation:

Area " length # width

The units for area are called square units, such as m2, cm2,and km2. Figure 25 will help you understand square units.

Figure 25 The area of thisrectangle is 20 cm2. If youcount the smaller squareswithin the rectangle, you’llcount 20 squares that eachmeasure 1 cm2.

Chapter 126

Figure 24 Measuring Temperature

212°F 100°CWater boils Water boils

98.6°F 37°CNormal body Normal bodytemperature temperature

32°F 0°CWater freezes Water freezes

Using Area to Find VolumeArea can be used to find thevolume of an object accord-ing to the following equation:

Volume " Area # height

1. What is the volume of abox 5 cm tall whose lidhas an area of 9 cm2?

2. A crate has a volume of 48 m3. The area of its bot-tom side is 16 m2. What isthe height of the crate?

3. A cube with a volume of8,000 cm3 has a height of20 cm. What is the area ofone of its sides?

MATH BREAK

˚F ˚C

-20

110

-100

020406080

100120140160180200220

102030405060708090100

!"

!"

5 cm

4 cm


Density Another derived quantity is density. Density is massper unit volume. So an object’s density is the amount of mat-ter it has in a given space. To find density (D), first measuremass (m) and volume (V ). Then use the following equation:

D " $mV

$

For example, suppose you want to know the density of the gear shown at right. Its mass is 75 g and its volume is 20 cm3. You can calculate the gear’s density like this:

D " $mV

$ " $75 g

$20 cm3 " 3.75 g/cm3

Safety Rules!Physical science is exciting and fun, but it can also be dan-gerous. So don’t take any chances! Always follow your teacher’sinstructions, and don’t take shortcuts—even when you thinkthere is little or no danger.

Before starting an experiment, get your teacher's permis-sion and read the lab procedures carefully. Pay particular atten-tion to safety information and caution statements. The chartbelow shows the safety symbols used in this book. Get to knowthese symbols and what they mean. Do this by reading thesafety information starting on page 512. This is important!If you are still unsure about what a safety symbol means, askyour teacher.


Stay on the safe side by readingthe safety information on page512. You must do this beforedoing any experiment!

1. Why is SI important?

2. Which SI unit would you use to express the height ofyour desk? Which SI unit would you use to express thevolume of this textbook?

3. Comparing Concepts How is area different from volume?

REVIEW

Safety Symbols

Eye protection

Heating safety

Chemical safety

Clothing protection

Electric safety

Animal safety

Hand safety

Sharp object

Plant safety


Chapter Highlights

Chapter 128

SECTION 1 SECTION 2

Vocabularyphysical science (p. 7)

Section Notes• Science is a process of mak-

ing observations and askingquestions about thoseobservations.

• Physical science is the studyof matter and energy and isoften divided into physicsand chemistry.

• Physical science is part of many other areas of science.

• Many different careersinvolve physical science.

Vocabularyscientific method (p. 11)technology (p. 11)observation (p. 12)hypothesis (p. 14)data (p. 16)theory (p. 19)law (p. 19)

Section Notes• The scientific method is a

series of steps that scientistsuse to answer questions andsolve problems.

• Any information you gatherthrough your senses is anobservation. Observationsoften lead to questions orproblems.

• A hypothesis is a possibleexplanation or answer to aquestion. A good hypothesisis testable.

• After you test a hypothesis,you should analyze yourresults and draw conclusionsabout whether your hypothe-sis was supported.

• Communicating your find-ings allows others to verifyyour results or continue toinvestigate your problem.

• A scientific theory is theresult of many investigationsand many hypotheses.Theories can be changed ormodified by new evidence.

• A scientific law is a summaryof many experimental resultsand hypotheses that havebeen supported over time.

LabsExploring the Unseen (p. 516)

Skills CheckVisual UnderstandingSCIENTIFIC METHOD To answer a question in science, you can use the scientific method.Review the flowchart on page 18 to see that thescientific method does not have to follow aspecific order.

MODELS A model is a representation of an object or system.Look back at the exampleson page 20 to learn moreabout different models.

Math ConceptsAREA To calculate the area of a rectangular surface, first measure its length and width, thenmultiply those values. The area of a piece ofnotebook paper with a length of 28 cm and awidth of 21.6 cm can be calculated as follows:

Area ! length " width

! 28 cm " 21.6 cm

! 604.8 cm2


29The World of Physical Science

SECTION 3 SECTION 4

Vocabularymodel (p. 20)

Section Notes• Scientific models are

representations of objects orsystems. Models makedifficult concepts easier tounderstand.

• Models can represent thingstoo small to see or too largeto observe directly.

• Models can be used to testhypotheses and illustratetheories.

LabsOff to the Races! (p. 517)

Vocabularymeter (p. 25)volume (p. 25)mass (p. 26)temperature (p. 26)area (p. 26)density (p. 27)

Section Notes• The International System of

Units is the standard systemof measurement used aroundthe world.

• Length, volume, mass, andtemperature are quantities ofmeasurement. Each quantityof measurement is expressedwith a particular SI unit.

• Area is a measure of howmuch surface an object has.Density is a measure of massper unit volume.

• Safety rules are importantand must be followed at alltimes during scientificinvestigations.

LabsMeasuring Liquid Volume (p. 518)Coin Operated (p. 519)

Visit the National Science Teachers Association on-line Website for Internet resources related to this chapter. Just type inthe sciLINKS number for more information about the topic:

TOPIC: Matter and Energy sciLINKS NUMBER: HSTP005TOPIC: The Scientific Method sciLINKS NUMBER: HSTP010TOPIC: Using Models in Physical Science sciLINKS NUMBER: HSTP015TOPIC: SI Units sciLINKS NUMBER: HSTP020

Visit the HRW Web site for a variety oflearning tools related to this chapter. Just type in the keyword:

KEYWORD: HSTWPS

GO TO: go.hrw.com GO TO: www.scilinks.org


Chapter ReviewUSING VOCABULARY

For each pair of terms, explain the differencein their meanings.

1. science/technology

2. observation/hypothesis

3. theory/law

4. model/theory

5. volume/mass

6. area/density

UNDERSTANDING CONCEPTS

Multiple Choice

7. Physical science is the study of a. matter and motion.b. matter and energy.c. energy and motion.d. matter and composition.

8. 10 m is equal to a. 100 cm. c. 10,000 mm.b. 1,000 cm. d. Both (b) and (c)

9. For a hypothesis to be valid, it must be a. testable.b. supported by evidence.c. made into a law.d. Both (a) and (b)

10. The statement “Sheila has a stain on her shirt” is an exampleof a(n) a. law.b. hypothesis.c. observation.d. prediction.

11. A hypothesis is often developed out of a. observations. c. laws.b. experiments. d. Both (a) and (b)

12. How many milliliters are in 3.5 kL? a. 3,500 c. 3,500,000b. 0.0035 d. 35,000

13. A map of Seattle is an example of a a. law. c. model.b. quantity. d. unit.

14. Which of the following is an example oftechnology? a. massb. physical sciencec. screwdriverd. none of the above

Short Answer

15. Name two areas of science other thanchemistry and physics, and describe howphysical science has a role in those areasof science.

16. Explain why the results of one experimentare never really final results.

17. Explain why area and density are calledderived quantities.

18. If a hypothesis is not testable, does thatmean that it is wrong? Explain.

Concept Mapping

19. Use the following terms to create aconcept map: science, scientificmethod, hypothesis,problems, questions,experiments,observations.

Chapter 130Copyright © by Holt, Rinehart and Winston. All rights reserved.

MATH IN SCIENCE

24. The cereal box at right has a mass of 340 g. Its dimensions are 27 cm ! 19 cm ! 6 cm.a. What is the volume

of the box?b. What is its density?c. What is the area of

the front side of the box?

INTERPRETING GRAPHICS

Examine the picture below, and answer thequestions that follow:

25. How similar to the real object is thismodel?

26. What characteristics of the real objectdoes this model not show?

27. Why might this model be useful?

CRITICAL THINKING AND PROBLEM SOLVING

20. A tailor is someone who makes or altersitems of clothing. Why might a standardsystem of measurement be helpful to atailor?

21. Two classmates are having a debate aboutwhether a spatula is an example of tech-nology. Using what you know about sci-ence, technology, and spatulas, write acouple of sentences that will help yourclassmates settle their debate.

22. Imagine that you are conducting anexperiment in which you are testing theeffects of the height of a ramp on thespeed at which a toy car goes down theramp. What is the variable in this experi-ment? What factors must be controlled?

23. Suppose a classmate says, “I don’t need to study physical science because I’m notgoing to be a scientist, and scientists arethe only people who use physical sci-ence.” How would you respond? (Hint: In your answer, give several examples ofcareers that use physical science.)

Take a minute to review your answersto the ScienceLog questions on page 5.Have your answers changed? If neces-sary, revise your answers based on whatyou have learned since you began thischapter.

The World of Physical Science 31Copyright © by Holt, Rinehart and Winston. All rights reserved.

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CHAPTER 1 The World of Physical Science · PDF fileNEW TERMS physical science OBJECTIVES! Describe physical science as the study of energy and matter.! Explain the role of physical