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16.1 Thermal Energy and Matter

Reading StrategyPreviewing Copy the table below. Beforeyou read, preview the figures in this sectionand add two more questions to the table. Asyou read, write answers to your questions.

Key ConceptsIn what direction doesheat flow spontaneously?

What is the temperatureof an object related to?

What two variables isthermal energy related to?

What causes thermalexpansion?

How is a change intemperature related tospecific heat?

On what principle does acalorimeter operate?

Vocabulary◆ heat◆ temperature◆ absolute zero◆ thermal expansion◆ specific heat ◆ calorimeter

In the 1700s, most scientists thought heat was a fluid called caloricthat flowed between objects. In 1798, the American-born scientistBenjamin Thompson (1753–1814), also known as Count Rumford,challenged this concept of heat. Rumford managed a factory thatmade cannons. Figure 1 shows how a brass cylinder was drilled tomake the cannon barrel. Water was used to cool the brass so that it didnot melt. Rumford observed that the brass became hot as long as thedrilling continued, producing enough heat to boil the water. Soon afterthe drilling stopped, however, the water stopped boiling. When thedrilling resumed, the water again came to a boil. Based on his observa-tions, Rumford concluded that heat could not be a kind of matter, butinstead was related to the motion of the drill.

Work and HeatA drill is a machine that does work on the cannon. Remember that nomachine is 100 percent efficient. Some of the work done by the drilldoes useful work, but some energy is lost due to friction. Frictioncauses the moving parts to heat up. The more work done by the drill,the more that friction causes the cannon to heat up.

Heat is the transfer of thermal energy from one object to anotherbecause of a temperature difference. Heat flows spontaneouslyfrom hot objects to cold objects. Heat flows from the cannon to thewater because the cannon is at a higher temperature than the water.

Which has more thermal energy,a cup of tea or a pitcher of juice?

Questions About Thermal Energy and Matter

b. ?

d. ?

c. ?

e. ?

a. ?

Answers

474

Figure 1 Count Rumfordsupervised the drilling of brasscannons in a factory in Bavaria.From his observations, Rumfordconcluded that heat is not a formof matter.

474 Chapter 16

FOCUS

Objectives16.1.1 Explain how heat and work

transfer energy.16.1.2 Relate thermal energy to the

motion of particles that makeup a material.

16.1.3 Relate temperature to thermalenergy and to thermalexpansion.

16.1.4 Calculate thermal energy,temperature change, or massusing the specific heat equation.

16.1.5 Describe how a calorimeteroperates and calculate thermalenergy changes or specific heatusing calorimetrymeasurements.

Build VocabularyConcept Map Have students constructa concept map of the vocabulary termsin this section. Instruct students to placethe terms in ovals and connect the ovalswith lines on which linking words areplaced. Students should place the mainconcept (Thermal Energy and Matter) at the top. As they move away from themain concept, the content shouldbecome more specific.

Reading StrategySample answers: a. A pitcher of juiceb. Why did Rumford conclude that heat is not a form of matter? c. The brass washot enough to make water boil onlyduring drilling, so the heat must berelated to the motion of the drill. d. Howis specific heat related to temperature?e. The lower a material’s specific heat, the more its temperature rises when agiven amount of energy is absorbed by a given mass.

INSTRUCT

Work and HeatFYIIt is common usage to talk about heatflowing. More precisely, it is thermalenergy that flows. It is always correct touse “heat” as a verb; using “heat” as anoun should be avoided.

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Reading Focus

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Section 16.1

Print• Reading and Study Workbook With

Math Support, Section 16.1 and Math Skill: Calculating with Specific Heat

• Math Skills and Problem SolvingWorkbook, Section 16.1

• Transparencies, Chapter Pretest andSection 16.1

Technology• Probeware Lab Manual, Lab 7• Interactive Textbook, Section 16.1• Presentation Pro CD-ROM, Chapter Pretest

and Section 16.1• Go Online, NSTA SciLinks, Specific heat

Section Resources

TemperatureHow do you know something is hot? You might use a thermometer tomeasure its temperature. Temperature is a measure of how hot or coldan object is compared to a reference point. Recall that on the Celsiusscale, the reference points are the freezing and boiling points of water.On the Kelvin scale, another reference point is absolute zero,which is defined as a temperature of 0 kelvins.

Temperature is related to the average kineticenergy of the particles in an object due to their randommotions through space. As an object heats up, its particlesmove faster, on average. As a result, the average kinetic energyof the particles, and the temperature, must increase.

Why does heat flow from a high to a low temperature?One way that heat flows is by the transfer of energy in col-lisions. On average, high-energy particles lose energy, andlow-energy particles gain energy in collisions. Overall, col-lisions transfer thermal energy from hot to cold objects.

Thermal EnergyRecall that thermal energy is the total potential and kineticenergy of all the particles in an object. Thermal energydepends on the mass, temperature, and phase (solid, liquid,or gas) of an object.

Thermal energy, unlike temperature, depends on mass.Suppose you compare a cup of tea and a teapot full of tea.Both are at the same temperature, so the average kineticenergy of the particles is the same in both containers.However, there is more thermal energy in the teapot becauseit contains more particles.

Now consider how thermal energy varies with tempera-ture. You can do this by comparing a cup of hot tea with acup of cold tea. In both cases, the tea has the same mass,and the same number of particles. But the average kineticenergy of particles is higher in the hot tea, so it also hasgreater thermal energy than the cold tea.

Figure 2 shows the particles in a cup of hot tea and in apitcher of lemonade. The tea is at a higher temperaturebecause its particles move a little faster, on average. But theyare only moving slightly faster, and the pitcher of lemonadehas many more particles than the tea. As it turns out, thepitcher of lemonade has more thermal energy than the cupof hot tea.

What is thermal energy?

5375& Associates

A

B

Figure 2 Thermal energy depends on mass andtemperature. A The tea is at a highertemperature than the lemonade because itsparticles have a higher average kinetic energy.B The lemonade is at a lower temperature, butit has more thermal energy because it has manymore particles. Inferring In which liquid arewater particles moving faster, on average?

Thermal Energy and Heat 475

Build Reading LiteracyMake Inferences Refer to page 472Din this chapter, which provides theguidelines for making inferences.

Students’ understanding often dependson how they apply prior knowledgetoward making inferences about newsituations. Have students read the twoparagraphs at the bottom of p. 474.Invite students to describe situationsthat are similar to the drill heated byfriction. Then, ask students to make aninference: Based on what you haveread, why do your hands feel warmerafter you rub them together? (Some ofthe work done is lost to friction, and so isconverted to thermal energy.)Logical

Temperature

Students may assume from common-usephrases such as heat transfer and heatflow that heat is a moving substance.Emphasize that heat is a flow, or transfer,of thermal energy from one object ormaterial to another, just as work is atransfer of mechanical energy. Whileconvection involves the movement ofparticles of a fluid from one place toanother, there is obviously no flow ofmatter when thermal energy is trans-ferred from one solid to another. Anamount of heat, like an amount of work,refers to how much energy is transferred.Verbal

Thermal EnergyUse VisualsFigure 2 Stress that the particles in both liquids are mostly water molecules,and that these are not simple spheres.Ask, In what ways can a water moleculemove? (Each molecule can move to thesides in three dimensions, rotate, andstretch along its molecular bonds.) Pointout that some kinetic energy is present in each of these motions, and this affectsthe overall temperature of the liquid.Visual

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Customize for English Language Learners

Reading/Learning LogConcepts such as heat, temperature, andthermal energy are easy to misunderstand andconfuse with each other. Be sure that Englishlanguage learners have a clear understanding

of these concepts by having them construct a Reading/Learning Log. Have students writewhat they understand in the left column, andwhat they still have questions about in theright column.

Answer to . . .

Figure 2 The average speed of waterparticles is greater in the tea becausethe average kinetic energy is greater.

Thermal energy is thetotal potential and kinetic

energy of all the particles in an object.

0472_hsps09te_Ch16.qxp 4/19/07 8:40 AM Page 475

476 Chapter 16

Thermal Contraction and ExpansionIf you take a balloon outside on a cold winter day, it shrinks. Can youexplain why? As temperature decreases, the particles that make up theair inside the balloon move more slowly, on average. Slower particlescollide less often and exert less force, so gas pressure decreases and theballoon contracts. This is called thermal contraction.

If you bring the balloon inside, it expands. Thermal expansion isan increase in the volume of a material due to a temperature increase.

Thermal expansion occurs when particles of matter move fartherapart as temperature increases. Gases expand more than liquids andliquids usually expand more than solids. A gas expands more easilythan a liquid or a solid because the forces of attraction among parti-cles in a gas are weaker.

Thermal expansion is used in glass thermometers. As temperatureincreases, the alcohol in the tube expands and its height increases. Theincrease in height is proportional to the increase in temperature. In anoven thermometer, a strip of brass and a strip of steel are bondedtogether and wound up in a coil. As the coil heats up, the two metalsexpand at different rates, and the coil unwinds. This causes the needleto rotate on the temperature scale.

Specific Heat When a car is heated by the sun, the temperature of the metal doorincreases more than the temperature of the plastic bumper. Do youknow why? One reason is that the iron in the door has a lower specificheat than the plastic in the bumper. Specific heat is the amount of heatneeded to raise the temperature of one gram of a material by one degreeCelsius. If equal masses of iron and plastic absorb the same heat, theiron’s temperature rises more. The lower a material’s specific heat,the more its temperature rises when a given amount of energy isabsorbed by a given mass.

Specific heat is often measured in joules per gram perdegree Celsius, or J/g•�C. Figure 3 gives specific heats fora few common materials. It takes 4.18 joules of energy toraise the temperature of 1.00 gram of water by 1.00 degreeCelsius. How much energy is needed to heat 2.00 grams ofwater to the same temperature? You would have to addtwice as much energy, or 8.36 joules.

What is thermal expansion?

Cooling Air

Procedure1. Inflate a round balloon and

then stretch its openingover the mouth of a 2-Lbottle. Use a tape measureto measure and record theballoon’s circumference.

2. Put a dozen ice cubes intoa plastic bucket. Add coldwater to the bucket to adepth of 15 cm. Submergethe bottom of the bottle inthe ice water and tape thebottle in place.

3. After 10 minutes, measureand record the circum-ference of the balloon.

Analyze and Conclude1. Observing How did

the volume of air in theballoon change?

2. Inferring Explain why theair behaved as it did.

Material (at 100 kPa) Specific Heat (J/g•�C)

Water

Plastic (polypropylene)

Air

Iron

Silver

4.18

1.84–2.09

1.01

0.449

0.235

Specific Heats of Selected Materials

Figure 3 Specific heat is the heat needed to raise the tempera-ture of 1 gram of material by 1ºC. Analyzing Data Which material in the table has the highest specific heat? The lowest?

Thermal Contraction and Expansion

Cooling Air

ObjectiveAfter completing this activity, studentswill be able to• describe the effect of temperature on

the volume of a gas.

Skills Focus Measuring, Comparingand Contrasting

Prep Time 20 minutes

Materials round balloon, 2-L plasticbottle, metric tape measure, plasticbucket, ice

Advance Prep The circumference ofthe balloon can be found by wrapping a string around the balloon and thenmeasuring the length of the string.

Class Time 20 minutes

Safety Students should wear safetygoggles and lab aprons and must wipeup any spills immediately to avoid falls.

Teaching Tips• Students can calculate the volume of

the balloon from its circumference by approximating the shape of the balloon as a sphere and using theequation C � 2�r to find the radius.The volume is then given by V � �r3.Make sure students include the bottleto determine the total volume of theenclosed air.

Expected Outcome The ballooncontracts as the air in the bottle cools.

Analyze and Conclude1. The volume decreased when cool.2. Cooling the air inside the bottle andballoon reduced the kinetic energy of itsparticles, and therefore the pressure onthe balloon, causing it to contract.Visual, Logical

Specific HeatBuild Science SkillsAnalyzing Data Have students examinethe specific heat values in Figure 3. Ask,Which substance requires nearly 1 J ofenergy to raise the temperature of 1 gby 1°C? (Air) What amount of energywould be required to raise the temper-ature of 2.00 g of water by 1.00°C?(4.18 � 2.00 � 8.36 J) Logical

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Section 16.1 (continued)

Thermal Contraction One of the fewexceptions to thermal expansion is water nearits freezing point. Over most temperatureranges, water increases in volume as itstemperature increases, but between 0°C and4°C water actually contracts as it gets warmer.This unusual behavior occurs because hydro-gen bonding between water molecules in ice

arranges them in a way that occupies a greatervolume than in liquid water. This results in ice being less dense than liquid water. In thewinter, when a pond begins to freeze, thedenser, warmer water sinks to the bottom, and the cooler, less dense ice floats. This formsa layer of warmer water at the bottom of thepond, in which fish are able to live.

Facts and Figures

476 Chapter 16


The heat (Q) absorbed by a material equals the product of the mass(m), the specific heat (c), and the change in temperature (ΔT).

Specific Heat Q � m � c � ΔT

In this formula, heat is in joules, mass is in grams, specific heat is inJ/g•°C, and the temperature change is in degrees Celsius.

Calculating Specific HeatAn iron skillet has a mass of 500.0 grams. The specific heat of ironis 0.449 J/g•°C. How much heat must be absorbed to raise theskillet’s temperature by 95.0°C?

Read and UnderstandWhat information are you given?

Mass of iron, m � 500.0 g

Specific heat of iron, c � 0.449 J/g•°C

Temperature change, ΔT � 95.0°C

Plan and SolveWhat unknown are you trying to calculate?

Amount of heat needed, Q � ?

What formula contains the given quantities andthe unknown?

Q � m � c � ΔT

Replace each variable with its known value.

Q � 500.0 g � 0.449 J/g•°C � 95.0°C

� 21,375 J � 21.4 kJ

Look Back and CheckIs your answer reasonable?

Round off the data to give a quick estimate.

Q � 500 g � 0.5 J/g•°C � 100°C � 25 kJ

This is close to 21.4 kJ, so the answer is reasonable.

1. How much heat is needed toraise the temperature of 100.0 gof water by 85.0°C?

2. How much heat is absorbed by a 750-g iron skillet when itstemperature rises from 25°C to 125°C?

3. In setting up an aquarium, theheater transfers 1200 kJ of heatto 75,000 g of water. What isthe increase in the water’stemperature? (Hint: Rearrangethe specific heat formula to solvefor ΔT.)

4. To release a diamond fromits setting, a jeweler heats a10.0-g silver ring by adding 23.5 J of heat. How much does the temperature of thesilver increase?

5. What mass of water will changeits temperature by 3.0°C when525 J of heat is added to it?

For: Links on specific heat

Visit: www.SciLinks.org

Web Code: ccn-2161

Build Math SkillsFormulas and Equations Studentsshould become familiar with rearrange-ments of the formula Q � m � c � �T, so that any one of these quantities can be calculated in terms of the other three.Have students rearrange the equation in order to calculate specific heat c � Q/(m � �T), mass m � Q/(c � ΔT),and temperature ΔT � Q/(m � c).Logical, Portfolio

Direct students to the Math Skills in the Skills and Reference Handbookat the end of the student text foradditional help.

Solutions1. Q � m � c � ΔT� (100.0 g)(4.18 J/g•°C)(85.0°C) � 35.5 kJ 2. Q � m � c � ΔT� (750 g)(0.449 J/g•°C)(125°C � 25°C)� (750 g)(0.449 J/g•°C)(100°C) � 34 kJ3. ΔT � Q/(m � c)� 1,200,000 J/(75,000 g � 4.18 J/g•°C)� 3.8°C 4. ΔT � Q/(m � c)� 23.5 J/(10.0 g � 0.235 J/g•°C) � 10.0°C 5. m � Q/(ΔT � c)� 525 J/(3.0°C � 4.18 J/g•°C) � 42 g Logical

For Extra HelpMake sure students start by writing out the equation required to solve eachproblem. Then, check that they are ableto solve the equation for the unknownvariable using basic algebra skills. Logical

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Answer to . . .

Figure 3 Silver has the lowest specific heat. Water has the highestspecific heat.

Thermal expansion is theincrease in volume of a

material due to a temperature increase.

Download a worksheet on specificheat for students to complete, andfind additional teacher supportfrom NSTA SciLinks.

Additional Problems1. Gold has a specific heat of 0.13 J/g•°C. If asample of gold with a mass of 250 g undergoes a temperature increase of 4.0°C, how much heatdoes it absorb? (130 J)2. A piece of iron at a temperature of 145.0°C coolsoff to a temperature of 45.0°C. If the iron has amass of 10.0 g and a specific heat of 0.449 J/g•°C,how much heat is given up? (449 J)Logical, Portfolio


478 Chapter 16

Section 16.1 Assessment

Reviewing Concepts1. In what direction does heat flow on its

own spontaneously?

2. How is the temperature of an objectrelated to the average kinetic energy ofits particles?

3. Name two variables that affect thethermal energy of an object.

4. What causes thermal expansion of anobject when it is heated?

5. How do the temperature increasesof different materials depend on theirspecific heats?

6. What principle explains how a calorimeteris used to measure the specific heat of asample material?

Critical Thinking 7. Applying Concepts Why is it necessary to

have regularly spaced gaps between sectionsof a concrete sidewalk?

8. Predicting An iron spoon and silver spoonhave the same mass. Which becomes hotterwhen both are left in hot tea for one minute?(Hint: Use the specific heats given in Figure 3.)

9. Calculating If it takes 80.0 joules to raise thetemperature of a material by 10.0�C, howmuch heat must be added to cause anadditional increase of 20.0�C?

10. The specific heat of copper is0.39 J/g•°C. How much heat is neededto raise the temperature of 1000.0 g ofcopper from 25.0°C to 45.0°C?

11. A peanut burned in a calorimetertransfers 18,200 joules to 100.0 g ofwater. What is the rise in the water’stemperature? (Hint: Rearrange thespecific heat formula to solve for �T.)

Measuring Heat Changes A calorimeter is an instrument used to measure changes inthermal energy. A calorimeter uses the principle that heatflows from a hotter object to a colder object until both reachthe same temperature. According to the law of conservationof energy, the thermal energy released by a test sample is equalto the thermal energy absorbed by its surroundings. Thecalorimeter is sealed to prevent thermal energy from escaping.

Figure 4 shows how a calorimeter can be used to measurethe specific heat of aluminum. A known mass of water isadded to the calorimeter. The mass of the sample of aluminumis measured. The aluminum is heated and then placed in thewater. The calorimeter is sealed. As the aluminum cools off,the water is stirred to distribute thermal energy evenly. Thewater heats up until both the aluminum and the water are at thesame temperature. The change in temperature of the water ismeasured. The thermal energy absorbed by the water is calcu-lated using the specific heat equation. Since this same amountof thermal energy was given off by the sample of aluminum,the specific heat of aluminum can be calculated.

Figure 4 A calorimeter is used to measurespecific heat. A sample to be tested is heatedand placed in the calorimeter. The lid is put onand the temperature change is observed.Hypothesizing Why does the calorimeterneed a stirrer?

ThermometerStirrer

Lid

Water

Aluminumsample

Calorimeter

Measuring HeatChanges

Calorimetry

Purpose Students observe a calorimetermeasuring changes in thermal energy.

Materials plastic foam cup with lid,thermometer, water, iron bolt (~75 g)

Procedure Place the iron bolt in afreezer for one hour prior to thedemonstration. Fill the cup two-thirds fullwith room-temperature water and recordits temperature. Place the cold iron in thewater and cover the cup. After threeminutes, record the temperature of thewater. Ask what students can infer aboutthe bolt’s initial temperature.

Safety Wipe up spills immediately.

Expected Outcome Students shouldconclude that the bolt was colder thanthe water. Visual, Group

ASSESSEvaluate UnderstandingAsk students to write a summaryparagraph relating thermal energy,temperature, and heat.

ReteachUse Figure 2 to summarize key conceptsabout thermal energy.

Solutions10. Q � m � c � ΔT � (1000.0 g) �(0.39 J/g•°C) � (45.0 � 25.0°C) � 7800 J11. ΔT � Q/(m � c)� 18,200 J/(100.0 g) (4.18 J/g•°C) � 43.5°C

If your class subscribesto the Interactive Textbook, use it toreview key concepts in in Section 16.1.

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6. A calorimeter uses the principle that heatflows from a hotter object to a colder objectuntil both reach the same temperature.7. The gaps provide space for concrete slabsto expand into so they do not buckle.8. Both spoons absorb the same energy and have the same mass. Because silver has alower specific heat (0.235 J/g•°C) than iron (0.449 J/g•°C), the silver becomes hotter.9. Doubling the temperature change doublesthe energy required, so 160 joules must be added.


1. Heat flows spontaneously from hot objectsto cold objects.2. Temperature is related to the averagekinetic energy of the particles in an object dueto their random motions through space.3. Mass of the object, temperature4. Particles of matter tend to move fartherapart as temperature increases.5. The lower a material’s specific heat, the moreits temperature increases when equal amountsof thermal energy are added to equal masses.

478 Chapter 16

Answer to . . .

Figure 4 The stirrer keeps tempera-ture uniform.

16.2 Heat and Thermodynamics

Reading StrategyBuilding Vocabulary Copy the table below.As you read, add definitions and examples tocomplete the table.

Key ConceptsWhy is conduction slowerin gases than in liquidsor solids?

In what natural cycles doconvection currents occur?

How does an object’stemperature affectradiation?

What are the three lawsof thermodynamics?

Vocabulary◆ conduction◆ thermal conductor◆ thermal insulator◆ convection◆ convection current◆ radiation◆ thermodynamics◆ heat engine◆ waste heat

To bake cookies, you put cookie dough on a baking sheet and pop itin the oven. When the timer goes off, you use oven mitts to pull out thebaking sheet. Why isn’t your bare arm burned by the hot air in the oven?One reason is that air is not a very good conductor of thermal energy.

ConductionConduction is the transfer of thermal energy with no overall transferof matter. Conduction occurs within a material or between materialsthat are touching. To understand conduction, look at the Newton’scradle in Figure 5. When a ball is pulled back and released, you mightexpect all of the balls to move to the right after the impact. Instead,most of the kinetic energy is transferred to one ball on the end. Similarly,in conduction, collisions between particles transfer thermal energy,without any overall transfer of matter.

Recall that forces are weak among particles ina gas. Compared to liquids and solids, the particlesin gases are farther apart. Conduction in gasesis slower than in liquids and solids because theparticles in a gas collide less often. In most solids,conduction occurs as particles vibrate in place andpush on each other. In metals, conduction is fasterbecause some electrons are free to move about.These free electrons collide with one another andwith atoms or ions to transfer thermal energy.

Conduction: transfer of thermalenergy without transfer of matter

Convection:

Radiation:

Definitions

a. ?

c. ?

Examples

Frying panhandle heats up.

b. ?

d. ?


Figure 5 Conduction is thetransfer of thermal energywithout transferring matter. Thisdevice, called Newton’s cradle,helps to visualize conduction.After one ball strikes the rest,most of the kinetic energy istransferred to one ball on the end.

FOCUS

Objectives16.2.1 Describe conduction,

convection, and radiation and identify which of these isoccurring in a given situation.

16.2.2 Classify materials as thermalconductors or thermalinsulators.

16.2.3 Apply the law of conservationenergy to conversions betweenthermal energy and otherforms of energy.

16.2.4 Apply the second law ofthermodynamics in situationswhere thermal energy movesfrom cooler to warmer objects.

16.2.5 State the third law ofthermodynamics.

Build VocabularyWord-Part Analysis Ask studentswhat words they know that have the keyword parts therm, con, duct, and radia.(Thermal energy, conductor, and radiator)Give a definition of a word part. (Thermmeans “heat,” con means “with,” ductmeans “to lead,” and radia means“rays.”) Give additional examples thatshare the word parts in question.(Thermometer, contact, deduct, radio)

Reading Strategya. The transfer of thermal energy by themovement of particles in a fluid b. Hot air circulates in an oven. c. The transfer ofenergy by waves moving through spaced. Heating coil of an electric stove glows.

INSTRUCT

ConductionUse VisualsFigure 5 Use the Newton’s cradle toreinforce why energy is transferred moreefficiently by conduction in a liquid orsolid. Ask, How could the balls bearranged to demonstrate conductionin a gas? (The balls could be detachedand spread on a table. When one ball isrolled toward any of the others, collisionswould occur only occasionally and withoutorder.)Visual

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Reading Focus

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Print• Laboratory Manual, Investigations 16A

and 16B• Reading and Study Workbook With

Math Support, Section 16.2• Transparencies, Section 16.2

Technology• Interactive Textbook, Section 16.2• Presentation Pro CD-ROM, Section 16.2• Go Online, NSTA SciLinks, Thermodynamics

Section Resources

Section 16.2

PPLS

0472_hsps09te_Ch16.qxp 3/6/07 1:54 PM Page 479

Thermal Conductors Figure 6 shows a frying pan on a hotstove. The bottom of the pan heats up first. The metal handle heats uplast. You can see that the flames do not directly heat the handle. Thehandle heats up because the metal is a good thermal conductor.

A thermal conductor is a material that conducts thermal energywell. A wire rack in a hot oven can burn you because the metal con-ducts thermal energy so quickly. Pots and pans often are made ofcopper or aluminum because these are good conductors.

A thermal conductor doesn’t have to be hot. Why does a tile floorfeel colder than a wooden floor? Both floors are at room temperature.But the tile feels colder because it is a better conductor and transfersthermal energy rapidly away from your skin.

Thermal Insulators Why is it safe to pick up the wooden spoonshown in Figure 6? Wood heats up slowly because it is a poor conduc-tor of thermal energy. A material that conducts thermal energy poorlyis called a thermal insulator.

Air is a very good insulator. A double-pane window has an air spacecontained between two panes of glass. The air slows down conductionto reduce heat loss in winter and to keep heat out of a building insummer. More expensive windows use argon gas, which is an even betterinsulator than air. Wool garments and plastic foam cups are two moreexamples of insulators that use trapped air to slow down conduction.

ConvectionConvection is the transfer of thermal energy when particles of a fluidmove from one place to another. Look at the people building a wallwith sandbags in Figure 7A. The moving sandbags are like the particlesin a fluid. The wall grows taller as more and more sandbags arrive. Inmuch the same way, particles in a fluid can transfer thermal energyfrom a hot area to a cold area.

Figure 6 The arrows show howthermal energy is conducted awayfrom the heat source in a metalfrying pan. Predicting Would itbe safe to touch the handle ofthe wooden spoon?

A

Figure 7 Convection is thetransfer of thermal energy by themovement of particles in a fluid.A Passing sandbags along a line islike transferring thermal energyby convection.B The arrows show convectionof air in an oven. Predicting Which part of theoven should have the highesttemperature?

B

Chapter 16

480 Chapter 16

Conductors and InsulatorsPurpose To show the similarities anddifferences between types of thermalconductors and insulators.Materials a block of wood, an aluminum pie plate, a metal spoon, a plastic spoon, a silk or cotton handker-chief, a metal screwdriver

Procedure Place the objects on a win-dowsill that is well-exposed to sunlight.Leave half of each object lying in thesunlight and the other half lying in theshade. Place the screwdriver so that thehalf of the metal shaft nearest the handleis in the shade. Leave the objects in thesunlight for at least 30 minutes. Haveeach student pick up each object by theend that has been in shade. Have themnote carefully any difference between the temperatures of the two ends of each object.

Safety Remind students that the partsof the objects that have been in sunlightmay be very hot.

Expected Outcome The pie plate, themetal spoon, and the shaft of the screw-driver are all metals, and so are goodthermal conductors. The parts of theseobjects that have been in the shadeshould feel warm. The wood, handker-chief, plastic spoon, and handle of thescrewdriver are thermal insulators, andshould not feel very warm. Kinesthetic, Group

ConvectionBuild Reading LiteracySequence Refer to page 290D inChapter 10, which provides theguidelines for a sequence.

Convection involves a sequence of steps.Have students describe the convection of warm air as a sequence of events,starting with “air heated by sunlight.”(The sequence may resemble the following:1) The temperature of the air increases.2) The air expands. 3) The less dense airrises while cooler, denser air sinks.) Logical

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Customize for Inclusion Students

Learning DisabledLearning-disabled students may processinformation in different ways, depending ontheir individual learning preferences andstrengths. Some may respond better to visualstimuli, while others may learn best throughthe aural or kinesthetic modes. In presentinginformation for these students, involve asmany modalities as possible. For example,

teach conduction by placing a stainless steelspoon and a plastic spoon in warm water.Have students observe the spoons andcompare the way they feel when they areremoved from the water. In similar ways,involve students’ aural, visual, and kinestheticsenses to reinforce your explanation ofscientific concepts.


Baking instructions sometimes tell you to use the top rack of anoven. Figure 7B shows why the temperature is lower at the top of theoven. When air at the bottom of the oven heats up, it expands andbecomes less dense than the surrounding air. Due to the difference indensity, the hot air rises. The rising air cools as it moves away from theheat source. As a result, the coolest air is at the top of the oven.

Air circulating in an oven is an example of a convection current. Aconvection current occurs when a fluid circulates in a loop as it alter-nately heats up and cools down. In a heated room, convection currentshelp keep the temperature uniform throughout the room.

Convection currents are important in many natural cycles, suchas ocean currents, weather systems, and movements of hot rock inEarth’s interior.

RadiationAt a picnic, you might use a charcoal grill to cook food. When youstand to the side of the grill, heat reaches you without convection orconduction. In much the same way, the sun warms you by radiation ona clear day. The space between the sun and Earth has no air to trans-fer thermal energy. Radiation is the transfer of energy by wavesmoving through space. Heat lamps used in restaurants are a familiarexample of radiation.

All objects radiate energy. As an object’s temperatureincreases, the rate at which it radiates energy increases. In Figure 8,the electric heating coil on a stove radiates so much energy that itglows. If you are close to the heating coil, you absorb radiation, whichincreases your thermal energy. In other words, it warms you up. Thefarther you are from the heating coil, the less radiation you receive,and the less it warms you.

What is radiation?

ObservingConvectionProcedure1. Fill a 100-mL beaker

halfway with cold water.

2. Fill a dropper pipet withhot water colored withfood coloring. Wipe thepipet with a paper towel sono food coloring is on theoutside of the pipet.

3. Insert the tip of the pipetinto the cold water,halfway between thesurface of the water andthe bottom of the beaker.

4. Slowly squeeze the pipetbulb. Observe the water inthe beaker from the side.

Analyze and Conclude1. Observing Describe the

motion of the colored hotwater in the beaker.

2. Inferring Explain why thehot water behaved as it did.

3. Predicting How wouldcolored cold water move ina beaker of hot water?

Figure 8 A heating coil on astove radiates thermal energy.The changing color of the redarrows indicates that the fartheryou are from the coil, the lessradiation you receive.

Observing Convection

ObjectiveStudents will learn to• use the concept of convection to

describe fluid motion.

Skills Focus Observing, Predicting


Advance Prep Provide a 500-mLbeaker of hot water with several dropsof food coloring.


Safety Turn off the hot plate at thestart of the activity. Remind students notto touch anything that is hot, to handleglassware carefully, and to wear safetygoggles and lab aprons.

Teaching Tips• Remind students to release the colored

water slowly, so that its movement willdepend only on its temperature.

Expected Outcome The colored watershould float to the top of the beaker.

Analyze and Conclude1. It rose to the top of the beaker andformed a visible layer there.2. The warm water rose to the top dueto convection.3. The cold water would sink. Visual, Logical

Radiation

Students may confuse the term radiationas it is used here with radiation fromnuclear decay. Explain that in both typesof radiation, energy spreads outward, or radiates, from a source. But nucleardecay such as alpha decay can alsotransfer mass. In thermal radiation, themass of an object does not changebecause only energy is transferred. Verbal

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Blackbody Radiation Radiation itself has no temperature because it does not consist ofmatter. Matter, however, can emit and absorbradiation. This changes the thermal energy,and thus the temperature, of an object. Agood emitter of radiation is also a goodabsorber of radiation. Because black surfacesabsorb radiation best, a perfect absorber andemitter of radiation is called an ideal blackbody

or blackbody. Blackbodies emit radiation at all wavelengths with a characteristic curve that depends on the temperature of theobject. By comparing the color and brightnessof the light emitted by an unknown radiatingobject to a blackbody with known properties,the temperature of the unknown object can be determined.

Facts and FiguresAnswer to . . .

Figure 6 Yes, because wood is not agood thermal conductor.

Figure 7 Hot air rises and cools, so thehighest temperature is at the bottom ofthe oven, where the heat source is.

Radiation is the transferof energy through space

without the help of matter to carry it.


ThermodynamicsThe study of conversions between thermal energy and other forms ofenergy is called thermodynamics. Count Rumford made a good startin this field. But many scientists still believed that heat was a kind ofmatter. Then in 1845, James Prescott Joule (1818–1889) published hisresults from a convincing experiment.

Joule carefully measured the energy changes in a system. Recallthat a system is any group of objects that interact with one another.Joule’s system included a falling weight that turned a paddle wheel ina container of water. As the weight fell, the paddle churned a knownmass of water. The water heated up due to friction from the turningpaddle. Joule carefully measured the work done by the falling weight.He found that the work almost exactly equaled the thermal energygained by the water. Joule is often given credit for discovering thefirst law of thermodynamics. That is the law of conservation ofenergy applied to work, heat, and thermal energy.

First Law of Thermodynamics Recall thatenergy cannot be created or destroyed. But energy can be con-verted into different forms. The first law ofthermodynamics states that energy is conserved. Ifenergy is added to a system, it can either increase the ther-mal energy of the system or do work on the system. But nomatter what happens, all of the energy added to the systemcan be accounted for. Energy is conserved.

Look at the bicycle pump in Figure 9. You can considerthe tire, the pump, and the air inside to be a system. Theforce exerted on the pump does work on the system. Someof this work is useful; it compresses air into the tire. Therest of the work is converted into thermal energy. That iswhy a bicycle pump heats up as you inflate a tire.

Second Law of Thermodynamics If you take acold drink from the refrigerator and leave it out in a warmroom, will the drink become colder? Of course it won’t.You know that the drink will warm up. Thermal energyflows spontaneously only from hotter to colder objects.

The second law of thermodynamics states thatthermal energy can flow from colder objects to hotterobjects only if work is done on the system. A refrigera-tor, for example, must do work to transfer thermal energyfrom the cold food compartment to the warm room air.The thermal energy is released by coils at the bottom or inthe back of the refrigerator.

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For: Links on thermodynamics

Visit: www.SciLinks.org

Web Code: ccn-2162

Figure 9 You can consider the bicycle pump, thetire, and the air inside of both to be a system. Theperson does work on the system by pushing onthe pump. Some of the work is converted intothermal energy, which heats the air in the pumpand the tire.

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ThermodynamicsBuild Science SkillsApplying Concepts

Purpose Students apply the concept of conservation of energy.

Materials putty (enough to make 1 golf ball-sized ball per student), table or desktop


Procedure Have students roll puttyinto balls about the size of a golf ball.Students hold the putty balls 2–3 feetabove a table or desk and then dropthem, noting the changes that occur.

Expected Outcome The potentialenergy of the putty ball held above thetable will be converted to kinetic energywhen the ball is released. Finally, it willstick to the table, and so undergo adecrease in kinetic and potential energy.According to the first law of thermody-namics, none of the energy is lost. Someof the mechanical energy is applied tochanging the shape of the putty ball. Therest is converted to increasing the thermalenergy of both the putty and the table,though increased thermal energy may notbe detectable due to the small amount ofenergy involved. Logical

Students may assume that addingenergy to a system by heating it will only increase the system’s thermalenergy. Explain that work may be done,or internal energy may increase (during a phase change). Sometimes the addedheat is mostly used to increase thethermal energy of the system, and littlework is done. Demonstrate this effect byplacing a sealed bottle of apple juice ona sunny windowsill. Only a small amountof work will be done because of the rigidwalls of the bottle, but the temperatureof the juice will increase. Work is negligi-ble compared to the amount of energyadded to the juice. Kinesthetic

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The “Zeroth” Law of ThermodynamicsIn order for a thermometer to give meaningfulinformation, its temperature must be equal to that of the object whose temperature isunknown. This occurs when both objects are in a state of thermal equilibrium, or when thethermal energy transferred by heat from theobject to the thermometer is equal to the heatfrom the thermometer to the object. This is thesame as saying that there is no net heat transferbetween the object and thermometer.

The definition of thermal equilibrium is the basis of what is called the “zeroth” law of thermodynamics—two systems in thermalequilibrium with a third system are in thermalequilibrium with each other. As the nameimplies, this concept is fundamental tothermodynamics, and the first three laws aredependent on it. The zeroth law was establish-ed after the first two laws of thermodynamicshad been accepted.

Facts and Figures

Download a worksheet onthermodynamics for students tocomplete, and find additionalteacher support from NSTA SciLinks.


Reviewing Concepts1. Why is conduction in gases slower than

conduction in liquids or solids?

2. Give three examples of convectioncurrents that occur in natural cycles.

3. What happens to radiation from an objectas its temperature increases?

4. State the first law of thermodynamics.

5. In your own words, what is the secondlaw of thermodynamics?

6. State the third law of thermodynamics.

7. Why does a metal spoon feel colder than awooden spoon at room temperature?

8. Why is solar energy transferred to Earth byradiation?

Critical Thinking9. Applying Concepts If your bedroom is cold,

you might feel warmer with several thinblankets than with one thick one. Explain why.

10. Relating Cause and Effect If everyobject is radiating constantly, why aren’tall objects getting colder?

A heat engine is any device that converts heat into work. One con-sequence of the second law of thermodynamics is that the efficiency ofa heat engine is always less than 100 percent. The best an engine can dois to convert most of the input energy into useful work. Thermal energythat is not converted into work is called waste heat. Waste heat is lost tothe surrounding environment. In fact, a heat engine can do work only ifsome waste heat flows to a colder environment outside the engine.

Spontaneous changes will always make a system less orderly, unlesswork is done on the system. For example, if you walk long enough,your shoelaces will become untied. But the opposite won’t happen;shoelaces don’t tie themselves. Disorder in the universe as a whole isalways increasing. You can only increase order on a local level. Forinstance, you can stop and tie your shoelaces. But this requires work.Because work always produces waste heat, you contribute to the dis-order of the universe when you stop to tie a shoelace!

Third Law of Thermodynamics The efficiency of a heatengine increases with a greater difference between the high tempera-ture inside and the cold temperature outside the engine. In theory, aheat engine could be 100 percent efficient if the cold outside envi-ronment were at absolute zero (0 kelvins). But this would violate thethird law of thermodynamics. The third law of thermodynamicsstates that absolute zero cannot be reached. Scientists have been ableto cool matter almost all of the way to absolute zero. Figure 10 showsthe equipment used to produce the record lowest temperature, just3 billionths of a kelvin above absolute zero!


Conservation of Energy Review energyconservation in Section 15.2. Describe howthe first and the second laws of thermody-namics are consistent with the law of con-servation of energy.

Figure 10 The third law ofthermodynamics states thatabsolute zero cannot be reached.This physicist is adjusting a laserused to cool rubidium atoms to 3 billionths of a kelvin aboveabsolute zero. This record lowtemperature was produced by a team of scientists at theNational Institute of Standardsand Technology.

Integrate Space ScienceAs the universe has expanded, its overalltemperature has decreased. Evidence ofthis is provided by background radiationthat astronomers detect in the universe.This radiation is left over from the bigbang, in which the universe was formed13.7 billion years ago. The radiation fills the universe uniformly, and so hasexpanded with the universe. As a result,the radiation has undergone a Dopplershift toward low-energy radio wavescalled microwaves. These microwaves correspond to the radiation emitted by ablackbody with a temperature of 2.7 K, orjust below three degrees above absolutezero. Were the universe to expand indef-initely, the background radiation wouldcontinue to decrease in energy, but itwould always be greater than zero, so thetemperature of the universe must alwaysbe above absolute zero.Logical

ASSESSEvaluate UnderstandingAsk students to list three examples eachof conduction, convection, and radiation.In each example, have them explain howthermal energy is transferred for thatexample and how energy is conserved in each case.

ReteachUse Figures 5 through 8 to review heattransfer, emphasizing how thermalenergy is changed in each case.

Energy is conserved in both laws. In thefirst law of thermodynamics, thermalenergy added to a system either increasesthe thermal energy of the system or isused to do work. In the second law ofthermodynamics, when work is done to transfer thermal energy from a coldobject to a hot object, some of the workis converted into thermal energy.

If your class subscribes tothe Interactive Textbook, use it toreview key concepts in Section 16.2.

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7. The metal feels colder because it is a betterthermal conductor, and it transfers energy morerapidly from the warm hand to the cool room.8. Radiation is the only type of energy transferthat can occur through a vacuum.9. The thin blankets trap air between thelayers, and air is a good insulator.10. Objects both radiate and absorb thermalenergy. If an object is cooler than itssurroundings, it absorbs more energy than itradiates, and so it heats up.


1. Because particles in a gas collide less oftenthan in a liquid or solid2. Ocean currents, weather systems, themovement of molten rock in Earth’s interior3. Its rate of radiation increases.4. The first law of thermodynamics states thatenergy is conserved.5. Heat can flow from a colder place to a warmerplace only if work is done on the system.6. Absolute zero cannot be reached.


Solar HomeHuge amounts of radiant energy fromthe sun constantly fall on the surface ofour planet. How can this energy beharnessed to help make a home that iswarm and comfortable in all seasons?

Heating a home with solar energy means makingthe best use of available sunlight. To providewarmth, large windows are placed on the southside of the house to trap sunlight, while north-facing walls have good insulation and fewwindows. On the roof, solar collectors absorbenergy from the sun’s rays to heat water, whilesolar panels convert the sun’s energy to electricalenergy for use in household appliances. High-quality insulation is used in all outside walls toreduce heat lost through convection, conduction,and radiation. But because the sun does not shinecontinuously, solar-heated homes also use energyfrom conventional sources to keep the homeheated day and night, year-round.

Large area of glass to trap radiant energy from the sun

Positioning for sunlightWindows should face south to trap asmuch light as possible from the wintersun, with few windows on the westside to reduce overheating in summer.

Automated louvers forcooling when needed

Trees on southand west sides for

summer shade

Planting trees and shrubs Trees placed away from the house act as a wind-break to reduce heat loss. Deciduous trees,planted closer, prevent overheating in summer,and allow sunlight to pass through in winter.

N

S

E

Evergreens provide ayear-round windbreak.

Deciduous trees give summer shade.

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EWintersun

N

WSummer sun

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Solar HomeBackgroundSolar heating for the home can consistof either “passive” systems, which donot use any mechanical device todistribute the fluids heated by the sun,or “active” systems that use fans orpumps to transfer the heated fluids.Although it is not practical to use solarheating systems to completely meetheating needs year round, solar heatingsystems can reduce the amount ofenergy used in conventional heatingsystems, thus reducing heating costs.

Build Science Skills

Observing

Purpose Students observe how passive solar heating can be used for heating.

Materials a box with black interior, a box with white interior, clear plasticwrap, 2 beakers, 2 thermometers

Class Time 50 minutes preparation, or one class period

Procedure Separate students intogroups, each with its own set of materials.Members of each group place one beaker,half full of water, in each of their boxesand cover both boxes with plastic wrap.Both boxes are placed in sunlight for halfan hour. Group members then removethe beakers from the boxes, placing athermometer in each. Finally, all studentsrecord the temperature of the water.

Safety Have students wear lab apronsand safety goggles.

Expected Outcome Because the blackbox absorbs and remits radiation betterthan the white box, the thermal energyof its walls and interior will be greater.The water will be in thermal equilibriumwith the interior of the box. Therefore,the water that had been in the black boxwill have a higher temperature than thewater in the white box.Kinesthetic, Group

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� Research solar-heated pools in the library or onthe Internet. Make a poster display explaininghow solar heating differs froma typical pool heating system.Include diagrams that explainhow radiation, absorption,insulation, and convection areused in a solar-heated pool.

� Take a Discovery Channel Video Field Trip by watching“Powered by the Sun.”

Going Further

Video Field Trip

Solar panelsSolar panels use the sun’s energyto generate electricity for thehome. The panels are made up ofa series of linked photovoltaiccells. Light from the sun releaseselectrons from silicon atoms inthe cells, producing an electriccurrent. Rechargeable batteriescan store electrical energy toprovide power when there is nosunlight.

Solar collectorto heat water

Well-insulatedtimber-framedwalls

Wood siding

Insulatingmaterial

Stud frame

Plasterboard

Heating system

Entertainment orcommunicationappliance

Cooking appliance

Electric circuit

Rechargeablebattery

Lighting

Airconditioning

system

Solar panelon roof

Small windows toreduce heat loss

Solar panel togenerate electricity

Wall insulation Wood is a natural

insulator, so timberconstruction reduces heat

flow through the walls.Filling the wall cavity

with insulating materialseals the walls against

drafts, and greatlyreduces heat loss.

Sun’s rays


Going FurtherStudent posters should clearly showenergy sources and energy transfers insolar-heated and conventionally heatedpools. Diagrams should label placeswhere radiation, absorption, andconvection occur. For example,absorption occurs in the solar collectorand convection occurs in the tubingthat carries heated water to the pool. Toreduce heat loss in a solar-heated pool,insulating plastic is placed on the water’ssurface when the pool is not in use. Visual


After students have viewed the Video Field Trip,ask them the following questions: How long isenergy from the sun expected to be available?(Billions of years) Why is it important to makeeffective use of solar energy? (Other sources ofenergy are being constantly used up.) How doesthe building at the Rocky Mountain Institutemanage to produce crops throughout the year?(By using a greenhouse with glass walls that let in

sunlight. Student answers may include that agreenhouse also stays warm inside partly by keepingout the colder air outside.) How does the heatingsystem in the Rocky Mountain Institute buildingproduce heat? (It converts sunlight into thermalenergy.) How does this heating system work?(Solar panels absorb sunlight and heat a fluid. Thefluid is pumped to a very large water tank. Heat fromthe stored hot fluid is transferred to the water thatpeople use. Students may comment that the watercan be heated to between 130°C and 140°C even inthe coldest weather.)

Video Field Trip

Powered by the Sun


Steam locomotives were one of the most important early uses of thesteam engine. Prior to the locomotive, steam engines provided powerfor coal mines and mills. But don’t think that steam engines are only athing of the past. In fact, most electric power plants today use steamturbines, a very efficient kind of steam engine.

Heat EnginesHeat engines played a key role in the development of the modernindustrial world. The two main types of heat engines are theexternal combustion engine and the internal combustion engine.

External Combustion Engine A steam engine is anexternal combustion engine—an engine that burns fuel outsidethe engine. Thomas Newcomen developed the first practical steamengine in 1712. His engine was used to pump water out of coalmines. In 1765, James Watt designed an engine that was more effi-cient, in part because it operated at a higher temperature.

Figure 11 shows one type of steam engine. Hot steam entersthe cylinder on the right side. When the valve slides to the left,hot steam is trapped in the cylinder. The steam expands andcools as it pushes the piston to the left. Thus heat is convertedinto work. The piston moves back and forth as hot steam entersfirst on one side and then on the other side.

16.3 Using Heat

Key ConceptsWhat are the two maintypes of heat engines?

How do most heatingsystems distribute thermalenergy?

How does a heat pumpreverse the normal flowof heat? Power

stroke: b. ?

Intake stroke:Fuel and air

enter cylinder.

Compressionstroke: a. ?

Exhauststroke: c. ?

Vocabulary◆ external

combustion engine◆ internal combustion

engine◆ central heating

system◆ heat pump◆ refrigerant

Reading StrategySequencing Copy the cycle diagram belowand complete it as you read to show thesequence of events in a gasoline engine.

Hot steam in

Slide valve

Exhauststeam out

Cylinder PistonPiston rod

Valverod

Figure 11 In an externalcombustion engine, combustionoccurs outside of the engine.

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FOCUS

Objectives16.3.1 Describe heat engines and

explain how heat enginesconvert thermal energy intomechanical energy.

16.3.2 Describe how the differenttypes of heating systemsoperate.

16.3.3 Describe how cooling systems,such as refrigerators and airconditioners, operate.

16.3.4 Evaluate benefits and draw-backs of different heating andcooling systems.

Build VocabularyLINCS Have students: List the parts ofthe vocabulary that they know, such ascentral, heating, system, heat, and pump.Imagine what a central heating systemmight look like and how the termsmight fit together. Note a reminding,sound-alike term, such as central nervoussystem or sound system. Connect theterms, perhaps in a long sentence or ashort story. Self-test (quiz themselves).

Reading Strategya. Piston compresses the fuel-air mixture.b. Ignited mixture expands and pushesthe piston. c. Exhaust gases leave thecylinder.

INSTRUCT

Heat EnginesBuild Reading LiteracyRelate Cause and Effect Refer to page 260D in Chapter 9, whichprovides the guidelines for relatingcause and effect.

Have students read the paragraphs aboutthe external combustion engine andstudy the illustration in Figure 11. Ask,What causes the piston in the cylinderto do work? (The expanding steampushes the piston, causing it to do work.)What is the effect of the movement ofthe slide valve? (It traps hot steam in thecylinder and allows cool steam to leave.)Logical

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Reading Focus

1

Section 16.3

Print• Reading and Study Workbook With

Math Support, Section 16.3• Math Skills and Problem Solving

Workbook, Section 16.3• Transparencies, Section 16.3

Technology• Interactive Textbook, Section 16.3• Presentation Pro CD-ROM, Section 16.3• Go Online, Science News, Heat

Section Resources

Intake strokeA Compression strokeB Power strokeC Exhaust strokeD

Intakevalve

Cylinder

Piston

Air-fuelmixture

Sparkplug

Exhaustvalve

Exhaustgases


Internal Combustion Engine Most cars use internal com-bustion engines that burn gasoline. An internal combustion engine isa heat engine in which the fuel burns inside the engine. Most internalcombustion engines use pistons that move up and down inside cylin-ders. Each upward or downward motion of a piston is called a stroke.The linear motion of each stroke is converted into rotary motion by thecrankshaft. The crankshaft is connected to the transmission, which islinked to the vehicle’s wheels through the drive shaft.

Figure 12 shows the sequence of events in one cylinder of a four-stroke engine. In the intake stroke, a mixture of air and gasoline vaporenters the cylinder. Next, in the compression stroke, the piston com-presses the gas mixture. At the end of compression, the spark plugignites the mixture, which heats the gas under pressure. In the powerstroke, the hot gas expands and drives the piston down. During theexhaust stroke, gas leaves the cylinder, and the cycle repeats.

Recall that a heat engine must discharge some waste energy in orderto do work. In an internal combustion engine, the cooling system andexhaust transfer heat from the engine to the environment. A coolant—usually water and antifreeze—absorbs some thermal energy from theengine and then passes through the radiator. A fan blows air through theradiator, transferring thermal energy to the atmosphere. Without acooling system, an engine would be damaged by thermal expansion. Ifyou are ever in a car that overheats, stop driving and allow the engineto cool. Otherwise, there is a risk of serious damage to the engine.

Gasoline engines are more efficient than old-fashioned steamengines, but they still are not very efficient. Only about one third of thefuel energy in a gasoline engine is converted to work. Auto makers havetried several ways to make engines more efficient. One design, called ahybrid design, uses a heat engine together with an electric motor. Thisdesign is explained in the How It Works box on the next page.

Figure 12 In an internalcombustion engine, fuel is burnedinside the engine. Most cars havea four-stroke internal combustionengine. This diagram shows onlyone of the cylinders during eachstroke. Classifying In which ofthe strokes does the piston dowork that can be used by the car?

For: Activity on four-stroke engines

Visit: PHSchool.com

Web Code: ccp-2163

Use Community ResourcesSuggest that students learn more aboutinternal combustion engines by visitingan auto repair shop and talking with amechanic. Encourage students toconstruct a KWL chart, and to ask themechanic questions based on whatstudents want to learn about engines.Interpersonal, Portfolio

Build Science SkillsApplying Concepts Have studentswrite a short paragraph about how theincreased temperature of the gasoline-air mixture allows it to do work duringthe power stroke in an internalcombustion engine. Remind them touse what they know about forms ofenergy and the relationship betweentemperature, pressure, and averagekinetic energy of particles that make upa substance. (Answers should indicatethat the energy released during ignition ofthe gasoline-air mixture increases themixture’s temperature, and thus theaverage kinetic energy of the gas particles.This greater energy produces an increasein gas pressure, which in turn does work.)Verbal, Logical

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Customize for English Language Learners

Simplify the PresentationThe details in the operations of heat engines,heat systems, and cooling systems are rathercomplex. By simplifying your presentation, theEnglish language learners in your class will have

a better comprehension of the material. Speakdirectly, use simple words and short sentences,and make frequent use of the diagrams toclarify the workings of thermal systems.

Answer to . . .

Figure 12 Work is done during thepower stroke as the expanding gasespush the piston out of the cylinder.

IPLS

For: Activity on four-stroke enginesVisit: PHSchool.comWeb Code: ccp-2163

Students can interact with asimulation of a four-stroke engineonline.


Tires These tires areinflated to a higherpressure than conventionaltires to reduce friction.

Transmission This convertsthe rotation of shafts in theelectric motor and the gasengine into wheel rotation. Inthis model, both the electricmotor and the engine candirectly drive the transmission.

Battery The batterystores energy for theelectric motor.

Fueltank

Electric motor The electricmotor is more efficientthan a heat engine foraccelerating at low speeds.When the brakes are used,the electric motor acts as agenerator, recharging thebatteries. This way of gen-erating power is calledregenerative braking.

Aerodynamic bodyThe teardrop shape

reduces air resistance,improving efficiency.

Lightweight materials A smallengine and synthetic materials, such

as carbon fiber, reduce the car’sweight to improve fuel efficiency.

Gasoline engine Thissmall heat engine is most

efficient for cruising atconstant speed. It is

assisted by the electricmotor during acceleration.

A new breed of carThis hybrid car was firstproduced in 1999. It is light,aerodynamic, and has asmall, efficient engine.

Hybrid AutomobileInternal combustion engines produce harmfulemissions from the combustion of gasoline. Recently,cleaner electric cars have been developed, but these needfrequent recharging. Hybrid cars solve these problems byusing a combination of smaller gasoline engines and electricmotors. Interpreting Diagrams Which features of thehybrid automobile help to reduce fuel consumption?

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Hybrid AutomobileThe hybrid automobile is a result ofresearch that was begun initially todevelop an efficient electric car. Bycombining a small gasoline engine withan electric motor, the hybrid automobileis able to travel longer distances, like agasoline-powered vehicle, but withreduced fuel consumption and emissions.During regenerative braking, kineticenergy that is normally lost to friction ispartially recovered for later use. This canbe explained to students in simple terms:It takes work to turn a generator. Whenthe spinning wheels do the work ofturning the generator, the wheels losekinetic energy. In other words, the wheelsmust slow down.

Interpreting Diagrams Fuelconsumption is reduced by usinglightweight materials, an aerodynamicdesign, and high-pressure tires thatreduce friction. The use of two enginessaves fuel because the small gasolineengine is more efficient than traditionallarger engines, and the electric motor ismore efficient than a gasoline engine foraccelerating at low speeds. Visual

For EnrichmentInterested students can make amultimedia presentation for the classexplaining the hybrid automobile.Numerous articles on the subject can be found on the Internet and in scienceand engineering periodicals.Verbal, Portfolio

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Heating SystemsAt the start of the industrial revolution, wood-burning fireplaces werethe principal method of heating buildings. Rumford was keenly awareof the drawbacks of fireplaces. They were smoky and not very efficient.Too much heat went up the chimney. In 1796, Rumford designed a fire-place that now bears his name. His fireplace was not as deep as standardfireplaces, and it had slanted walls to reflect heat into the room. Hisimprovements were quickly accepted and used throughout England.

Today, fireplaces are often used to supplement central heating sys-tems. A central heating system heats many rooms from one centrallocation. The central location of a heating system often is in thebasement. The most commonly used energy sources for central heat-ing systems are electrical energy, natural gas, oil, and coal. Heatingsystems differ in how they transfer thermal energy to the rest of thebuilding. Most heating systems use convection to distributethermal energy.

Hot-Water Heating Figure 13 shows the main components ofa hot-water heating system. At the boiler, heating oil or natural gasburns and heats the water. The circulating pump carries the hot waterto radiators in each room. The hot water transfers thermal energy tothe radiator by conduction. As the pipes heat up, theyheat the room air by conduction and radiation. Hot airrises and sets up a convection current in each room.After transferring much of its thermal energy to theroom, the cooled water returns to the boiler and thecycle begins again.

Temperature is controlled by a thermostat. Onekind of thermostat is like a thermometer, with a strip ofbrass and steel wound up in a coil. When the heatingsystem is on, the coil heats up. The two metals in thecoil expand at different rates, and the coil rotates. Thistrips a switch to turn off the heat. As the room cools,the coil rotates in the opposite direction, until it tripsthe switch to turn the heat back on.

Steam Heating Steam heating is very similar tohot-water heating except that steam is used instead ofhot water. The transfer of heat from the steam-heatedradiator to the room still occurs by conduction andradiation. Steam heating often is used in older build-ings or when many buildings are heated from onecentral location.

How are fireplaces often used today?

Figure 13 Within the pipes ofthis hot-water heating system, thewater circulates in a convectioncurrent. In each room, the airmoves in a convection current.Relating Cause and Effect Whyhas the water returning to theboiler cooled down?

Exhaustvent

Circulatingpump

Boiler

Radiator

Thermostat

Expansiontank

Heating Systems

Students may think that heating systemsare simply energy conversion devicesbecause they can use a variety of energysources to produce thermal energy.Remind students that the energy requiredto operate a heating system exceeds theamount of thermal energy distributed bythe system, partly because there is alwayssome energy that is lost through exhaustin the original central heating process. In addition, energy is lost through heattransfer processes from pipes and ductsthat transfer heated fluids from the centralheating system to the various rooms. Evenin electric heating, some energy is lost inheating the wires used to transfer electri-cal energy to the heating coils.Logical

Use VisualsFigure 13 Point out that the systemshown must be well insulated so as toprevent the loss of heat. Have studentslook at the various parts of the hot-waterheating system. Ask, Where canthermal energy be lost in this system,and by what manner of heat transfer?(Energy is lost through the water pipesleading from the boiler to the radiator.Most of this energy is lost by radiation,though some conduction to the air takesplace. A good deal of energy is lost byconvection from the exhaust vent. Asmaller amount of heat is lost through thepipes leading from radiators to the boiler.)Visual

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Answer to . . .

Figure 13 Water returning to theboiler has cooled because it has lostthermal energy in the radiator.

Today, fireplaces areoften used to supple-

ment central heating systems.

Heat of Vaporization Although hot-waterheating and steam heating systems are similarin structure, steam systems convey moreenergy for each kilogram of water used. Thisdifference occurs because the phase changethat takes place during the boiling process,when liquid water is vaporized to steam,requires a much greater input of energy than isnecessary to heat water in a hot-water system.The energy required for this phase change,

called the heat of vaporization, is equal to 2.26 � 106 J/kg. This amount is more than 500 times as great as the energy required toraise the temperature of a kilogram of liquidwater by 1°C (about 4180 J/kg). When steamcompletely condenses to liquid water, anamount of energy equal to the heat ofvaporization is given up. This is why steamheating is effective, and also why steam is so hazardous.

Facts and Figures


490 Chapter 16

Electric Baseboard Heating An electricbaseboard heater uses electrical energy to heat aroom. A conductor similar to the heating elementin an electric stove is used to convert electricalenergy to thermal energy. The hot coil heats theair near it by conduction and radiation. Then con-vection circulates the warm air to heat the room.

Radiant heaters are similar to electric base-board heating. They are often sold as smallportable units, and are used to supplement acentral heating system. These “space heaters” areeasy to turn on and off and to direct onto coldtoes or other areas where heat is needed most.Sometimes these heaters have a fan that helps tocirculate heat.

Forced-Air Heating To maintain evenroom temperatures, forced-air heating systemsuse fans to circulate warm air through ducts tothe rooms of a building. In a forced-air heatingsystem, shown in Figure 15, convection circulatesair in each room. Because the warm air enteringthe room rises toward the ceiling, the warm-airvents are located near the floor. Cool room airreturns to the furnace through floor vents on theother side of the room. One advantage of forced-air heating is that the air is cleaned as it passesthrough filters located near the furnace.

Cooling SystemsMost cooling systems, such as refrigerators and air conditioners, areheat pumps. A heat pump is a device that reverses the normal flow ofthermal energy. Heat pumps do this by circulating a refrigerantthrough tubing. A refrigerant is a fluid that vaporizes and condensesinside the tubing of a heat pump. When the refrigerant absorbs heat,it vaporizes, or turns into a gas. When the refrigerant gives off heat, itcondenses, or turns back into a liquid.

Recall that thermal energy flows spontaneously from hot objects tocold objects. Heat pumps must do work on a refrigerant in orderto reverse the normal flow of thermal energy. In this process, a coldarea, such as the inside of a refrigerator, becomes even colder.

How do forced-air heatingsystems circulate air?

For: Articles on heat

Visit: PHSchool.com

Web Code: cce-2163

ChimneyReturnvent

Supplyvent

Furnace

Duct

Hot airrises

Cool airsinks

Figure 14 In a forced-air central heatingsystem, the hot air enters the room througha supply vent in the floor. The hot air rises ascooler, denser air in the room sinks. Thecooler air returns to the furnace through thereturn vent. Inferring If the hot air supplyvent were located near the ceiling, whatwould be the warmest part of the room?

490 Chapter 16

Cooling Systems

Cooling by EvaporationPurpose Students observe howevaporation of a liquid can cool itssurroundings.

Materials paper towels, water, tape,hand-held or electric fan, thermometer

Procedure Wrap a wet paper towelaround the bulb of a thermometer andwait several minutes. Record the ther-mometer’s temperature. Tape the wetpaper towel to the thermometer’s bulb.Blow air across the paper towel with thefan. Read the thermometer’s tempera-ture again.

Safety Clean up any spills immediately.Handle thermometers with care to avoidbreakage. Be sure cords are untangledand cannot trip anyone. Do not handleelectrical equipment with wet hands.

Expected Outcome Water absorbsenergy as it evaporates. This removesenergy from the thermometer bulb, so the temperature reading of thethermometer decreases.Kinesthetic, Visual

Integrate ChemistryDifferent compounds can be used asrefrigerants, just as long as they can bemade to evaporate at low temperatures.Among the refrigerants that have thisproperty are certain chlorofluorocarbons,or CFCs, which have been used widelyin refrigerators and air conditioners. Inthe 1970s, chlorine atoms released byCFCs were found to react with the layerof atmospheric ozone, which absorbsharmful ultraviolet radiation from thesun. The decomposition of the ozonelayer prompted the establishment of theMontreal Accords in 1990 and theeventual replacement of CFCs with lessharmful refrigerants. Verbal, Logical

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Science News provides studentswith current information on heat.

Refrigerators A refrigerator is a heat pump—it transfers thermal energy from the cold foodcompartment to the warm room. To move heatfrom a colder to a warmer location, a motor mustdo work to move refrigerant through tubing insidethe refrigerator walls. Could you cool your kitchenon a hot day by leaving the refrigerator door open?It might seem so, but an open refrigerator wouldactually heat the kitchen! You may have noticed thehot coils underneath or behind the refrigerator. Thecoils not only release heat absorbed from the foodcompartment; they also release thermal energy pro-duced by the work the motor does. That is why arefrigerator with an open door adds more heat tothe room than it removes.

What is a heat pump?

What Is the Real Cost of aWashing Machine?

If you ever shop for a new washing machine, you’llnotice the bright yellow Energy Guide sticker oneach machine. The sticker gives the machine’soperating cost per year as estimated by the U.S.Department of Energy. The largest part of the costfor cleaning clothes is heating the water that goesinto the washing machine. So a machine that usesless water is more efficient.

1. Using Graphs One family uses an electricwater heater. What is their cost per year formachine A? For machine D?

2. Calculating How much money does thisfamily save each year using machine Acompared to using machine D?

3. Calculating The price of machine A is $300more than the price of machine D. If thefamily uses a machine for 10 years, which

Co

st p

er Y

ear

Washing Machines

Comparing Washing Machines

Brand A Brand B Brand C Brand D

$70

$60

$50

$40

$30

$20

$10

Electric water heater

Gas water heater

Temperature inroom: 25�C

Temperatureinside

refrigerator: 3�C

Figure 15 When a refrigerator door is open, somethermal energy from the room enters the refrigerator. But more thermal energy leaves the refrigerator throughthe coils underneath the food compartment. Interpreting Photos Why can’t you cool a room byleaving the refrigerator door open?


one costs less overall? (Hint: Add the price tothe operating cost for 10 years.)

4. Calculating Another family uses a gas waterheater. Which machine should this familychoose? Explain your thinking.

5. Evaluating and Revising A washing machineadvertisement states that the annual costassumes an electric water heater is used. Whywould an advertisement include only this cost?

What Is the Real Cost of a Washing Machine?Answers1. The annual cost of Brand A is about$10 per year. The annual cost of Brand Dis $60 per year.2. The family saves $50 each year usingBrand A.3. The operating cost of Brand A for 10 years is 10 � $10 � $100. Theoperating cost of Brand D for 10 years is 10 � $60 � $600. Brand A costs lessoverall because although the initial priceis $300 higher, the machine saves $500in operating costs.4. Using a gas water heater, Brand A savesonly $20 in operating costs each year.Based only on cost, the family shouldchoose Brand D because it will cost $100less to own and operate for 10 years.5. The goal of the advertisement is toconvince as many people as possible to buy the machine. Therefore, theadvertisement emphasizes the moneythat could be saved under the best of circumstances (using an electric water heater).

For Extra HelpDiscuss the basic features of a bar graph.Unlike line graphs, in which one quantityon the horizontal axis corresponds to aunique quantity on the vertical axis, morethan one bar can be given for a particularitem on the horizontal axis. For instance,in the above graph, each brand has twobars shown: one for electric heaters andone for gas heaters. Similarly, a compari-son between results in different years canbe shown using several bars. The place-ment of the bars allows easy comparisonof changes on one graph. Visual

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Answer to . . .

Figure 14 The ceiling, because warmair entering the room tends to remainnear the ceiling

Figure 15 The refrigerator gives offmore thermal energy than it absorbs.

In a forced-air heatingsystem, fans circulate

warm air through ducts to the roomsof a building.

A heat pump is a devicethat reverses the normal

flow of thermal energy.

Water Cooling Although refrigerants are usedto reach temperatures below the freezing pointof water, water itself has been used for coolingfor centuries. Because of its specific heat andheat of vaporization, water can greatly reducethe temperature of hot dry air. Fountains helped

to cool the air in courtyards in places like Spainand Italy. In many desert cities, evaporativecoolers, in which hot air is drawn through water-soaked pads into houses, are still widely used forair conditioning.

Facts and Figures


492 Chapter 16


Reviewing Concepts1. List the two main types of heat engines.

2. How is thermal energy distributed in mostheating systems?

3. How does a heat pump move thermalenergy from a cold area to a warm area?

4. If the efficiency of a gasoline engine is25 percent, what happens to the missing 75percent of the energy in the fuel?

Critical Thinking5. Predicting A diesel engine runs at a higher

temperature than a gasoline engine. Predictwhich engine would be more efficient. Explainyour answer.

6. Applying Concepts Why would it be amistake to locate a wood-burning stove onthe second floor of a two-story house?

Air Conditioners Have you ever beenoutside on a hot day and stood near a room airconditioner? The air conditioner is actuallyheating the outdoor air. Near the air conditioneris the last place you’d want to be on a hot day!

Where does the hot air come from? It mustcome from inside the house. But as you knowfrom the second law of thermodynamics, heatonly flows from a lower temperature (indoors)to a higher temperature (outdoors) if work isdone on the system.

Figure 16 shows how a room air conditioneroperates. The compressor raises the tempera-ture and pressure of the refrigerant, turning itinto a hot, high-pressure gas. The temperatureof the condenser coil is higher than the outside

air temperature, so heat flows spontaneously from the coil to the out-side air. A fan increases the rate at which heat flows. As thermal energyis removed from the coil, the refrigerant cools and condenses into a liquid.

The liquid refrigerant then flows through the expansion valve anddecreases in temperature. As the cold refrigerant flows through theevaporator coil, it absorbs thermal energy from the warm room air.The fan sends cold air back into the room. The refrigerant becomes avapor, and the process starts all over again.

Writing to Persuade Imagine that you area marketing executive in a company that sellsHVAC (heating, ventilation, and air condition-ing) equipment. Write a one-page flyer com-paring four kinds of heating systems. Organizethe flyer so it is easy for customers to see thebenefits of each system.

Figure 16 In a window airconditioner, outside air is heatedas a fan blows it through thecondenser coil. Inside the room, afan draws in warm air through theevaporator coil. The fan blowscooled air out into the room.Interpreting Diagrams Whatwork is done by the compressor?

Warmair in

Coldair out

Evaporator coilLiquid absorbs heatto become vapor.

Warmair out

Compressor

Condenser coilVapor cools to liquidas heat is removed.

Expansion valvePressure drops, causing liquid

refrigerant to become cold.

492 Chapter 16

Use VisualsFigure 16 Stress that evaporation is the key process for cooling in an airconditioner and refrigerator. Most of thework done by the air conditioner motorinvolves changing the pressure of therefrigerant so that it will evaporate (and soabsorb thermal energy) and condense (togive up thermal energy) easily. Ask, Whatis the direction of the net flow ofthermal energy in an air conditioner?(Looking at the red arrows only, thermalenergy is transferred from the air inside theroom to the outdoor air.)Visual

ASSESSEvaluate UnderstandingAsk students to write two questions eachabout heating systems and coolingsystems. Review the questions foraccuracy, and then have students form groups and ask each other theirapproved questions.

ReteachUse Figure 12 to review how an internalcombustion engine operates during one cycle.

Student flyers should clearly comparefour heating systems. Students maychoose to show the comparisons using achart. Possible columns in the chart areefficiency, physical space used per room,environmental concerns, and localclimate. Students may choose tocompare systems in different climates. Insouthern states, a benefit of a forced-airheating system is that it combines easilywith central air conditioning. Electricbaseboard heating is advantageous in regions where electric power isinexpensive.

If your class subscribes tothe Interactive Textbook, use it toreview key concepts in Section 16.3.

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the temperature inside and the temperatureoutside the engine. A diesel engine is likely to be more efficient, assuming both enginesdischarge thermal energy into an environmentat the same temperature.6. Convection will carry cool air to the lowerlevel so the lower level will be cooler than theupper level. This is inefficient because if thelower level is comfortable, the upper level willbe warmer than necessary.


1. External combustion engine, internalcombustion engine2. Most heating systems distribute thermalenergy by convection.3. Heat pumps must do work on a refrigerantin order to reverse the normal flow of heat.4. The energy that does not do useful work isconverted into thermal energy.5. The maximum efficiency of a heat engineincreases with a greater difference between

Answer to . . .

Figure 16 The compressor does workby pushing particles of vapor closertogether to form a high-pressure vapor.It also does work as it pushes refriger-ant through the tubing.

Thermal Energyand Heat

C H A P T E R

472 Chapter 16

As this locomotive steams along, it uses �thermal energy to do the work of climbing a hill.

How do science concepts apply to yourworld? Here are some questions you’ll beable to answer after you read this chapter.

■ When a car has been warmed by the sun, why is the metal door hotter than the plastic bumper? (Section 16.1)

■ Why doesn’t hot air burn your unprotected arm when you reach into an oven? (Section 16.2)

■ Why does a bicycle pump heat up when you pump up a tire? (Section 16.2)

■ What energy-saving strategies are used in a solar-heated home? (page 484)

■ Why must a car engine have a cooling system?(Section 16.3)

■ Can you cool a kitchen by leaving the refrigerator door open? (Section 16.3)

472 Chapter 16

ASSESS PRIORKNOWLEDGEUse the Chapter Pretest below to assessstudents’ prior knowledge. As needed,review these Science Concepts andMath Skills with students.

Review Science ConceptsSection 16.1 Review work, kineticenergy, and thermal energy. Remindstudents of the Celsius and Kelvintemperature scales used in science.Review how matter consists of atoms,ions, and molecules.

Section 16.2 Review efficiency ofmachines and the law of conservation ofenergy. Remind students of the definitionof absolute zero.

Section 16.3 Review the states ofmatter. Review chemical energy andenergy conversions.

Review Math SkillsScientific Notation, Calculatingwith Significant Figures, Formulasand Equations Students will need tomanipulate 4-variable formulas tocalculate specific heat.

Direct students to the Math Skills in theSkills and Reference Handbook at theend of the student text.

PHYSICS

Chapter 16

Chapter Pretest

1. True or False: Degrees Celsius and kelvinsare units of temperature. (True)2. What kind of energy is released whenbonds between atoms are broken? (Chemical energy)3. True or False: Thermal energy is the totalpotential and kinetic energy of the micro-scopic particles in an object. (True)4. The change of state from liquid to gas iscalled . (vaporization)

5. Which of the following is the energy of a moving object? (d)

a. Mechanical energyb. Chemical energyc. Potential energyd. Kinetic energy

6. The principle that energy cannot becreated or destroyed is known as the law of

.(conservation of energy)

7. Define work. (Work is a transfer of energy.)8. If the input work for a simple machine is 21.0 J, and the output work is 7.0 J, the efficiency of the machine is

. (c)a. 3.0%b. 0.33%c. 33%d. 30%

PHYSICS

16.1 Thermal Energy andMatter

16.2 Heat andThermodynamics

16.3 Using Heat

Chapter Preview

Video Field Trip

Powered by the Sun

What Happens When Hot and Cold Liquids Mix?Procedure1. Fill one graduated cylinder with hot water

and another with cold water. CAUTION Becareful when handling hot liquids. Use athermometer to measure the temperature ofthe water in each graduated cylinder. Recordthe temperatures.

2. Pour 100 mL of hot water into a plastic foamcup. Add 100 mL of cold water to the cup.Stir the water with a glass rod, and measureand record its temperature.

3. Repeat Step 2, this time adding 50 mL of coldwater to 100 mL of hot water.

Think About It1. Comparing and Contrasting How did the

final temperatures in Steps 2 and 3 compare?

2. Relating Cause and Effect What factorscan you identify that determine the finaltemperature when you mix hot water withcold water?

3. Controlling Variables Why do you think itwas important to use the same graduatedcylinders in Step 3 that you used in Step 2?



Encourage students to view the Video Field Trip“Powered by the Sun.”

ENGAGE/EXPLORE

Video Field Trip

Powered by the Sun

What Happens When Hot and Cold Liquids Mix?Purpose Students recognize that thefinal temperature of a mixture dependson the masses and temperatures of thesubstances that are mixed.

Students may think that because thetemperature of the cold water added isthe same for both mixtures, the finaltemperature should be similar. To helpremedy this misconception, ask whatelse may affect the final temperature.

Skills Focus Observing, Inferring,Measuring


Materials 2 plastic foam cups, glassstirring rod, thermometer, 2 100-mLgraduated cylinders


Safety Students should use tongs or wear heat-resistant gloves whenhandling hot glassware. Use non-mercury thermometers.

Teaching Tips• Hot and cold tap water should be

sufficient to show the desired results.Water could be cooled in a freezer toincrease the temperature difference.

• Students should stir the mixturesbefore measuring the temperature.

• Students should do the first trialrapidly so that the water temperaturesare the same for both trials.

Expected Outcome The cup thatreceived 100 mL of cold water will be cooler.

Think About It1. The mixture to which 50 mL of cold water was added had a highertemperature.2. Students may cite the temperaturesand “amounts” of water added. Theymay also say that energy or heat changedthe temperature of the water.3. Using the same source of hot and coldwater ensures that the temperatures usedwill be close to the same in both trials.Logical, Group

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In this lab, you will determine the specific heat ofsteel and aluminum. Then you will use specific heatto analyze the composition of a metal can.

Problem How can you use specific heat todetermine the composition of a metal can?

Materials

For the probeware version of this lab, seethe Probeware Lab Manual, Lab 7.

Skills Calculating, Designing Experiments

Procedure

Part A: Determining Specific Heat1. Copy the data table shown below.

2. Measure and record the mass of 10 steel bolts.

3. Tie the bolts to the string. Use a clamp andring stand to suspend the bolts in the boilingwater bath. CAUTION Be careful not to splashboiling water. After a few minutes, record thewater temperature as the initial temperature ofthe bolts.

4. Use a graduated cylinder to pour 200 mL ofice water (without ice) into the foam cup.Record the mass and temperature of the icewater. (Hint: The density of water is 1 g/mL.)

• 10 steel bolts• balance• 50-cm length

of string• clamp• ring stand• boiling water bath

(shared with class)

• thermometer• 500-mL graduated

cylinder• ice water• foam cup with lid• aluminum nails• crushed can

5. Use the clamp to move the bolts into the cupof ice water. Cover the cup and insert thethermometer through the hole in the cover.

6. Gently swirl the water in the cup. Record thehighest temperature as the final temperaturefor both the water and the steel bolts.

7. Calculate and record the specific heat of steel.(Hint: Use the equation Q � m � c � �T tocalculate the energy the water absorbs.)

8. Repeat Steps 3 through 7 with aluminum nailsto determine the specific heat of aluminum.Start by making a new data table. Use a massof aluminum that is close to the mass you usedfor the steel bolts.

Part B: Design Your Own Experiment9. Designing Experiments Design an

experiment that uses specific heat to identifythe metals a can might be made of.

10. Construct a data table in which to record yourobservations. After your teacher approves yourplan, perform your experiment.

Analyze and Conclude1. Comparing and Contrasting Which metal

has a higher specific heat, aluminum or steel?

2. Drawing Conclusions Was the specific heatof the can closer to the specific heat of steel orof aluminum? What can you conclude aboutthe material in the can?

3. Evaluating Did your observations provewhat the can was made of? If not, what otherinformation would you need to be sure?

4. Inferring The can you used is often called atin can. The specific heat of tin is 0.23 J/g•�C.Did your data support the idea that the canwas made mostly of tin? Explain your answer.

Data Table

Initial temperature (�C)Final temperature (�C)

Water Steel Bolt

4.18Specific heat (J/g•�C)

Mass (g)

Using Specific Heat to Analyze Metals

Using Specific Heat to Analyze MetalsObjectiveAfter completing this lab, students willbe able to• describe how specific heat is

determined.

Students may have the misconceptionthat the temperatures of the metal andwater are the only factors that will affectthe final temperature of the mixture. Tohelp dispel this misconception, ask themto compare the effects of dropping an icecube into a lake and into a glass of water.

Skills Focus Calculating,Measuring, Designing Experiments


Advance Prep Crush a steel can foreach lab group. Smooth any rough orsharp edges with a file while wearingheavy leather gloves and safety goggles.Puncture the lids of the foam cups toenable students to insert the thermo-meters. Provide a large beaker of boilingwater (with a thermometer in it) on a hotplate for the entire class to use. Providering stands, clamps, and 50-cm lengths of string for suspending the bolts in theboiling water bath.


Safety Provide only nonmercury ther-mometers. Students should use tongs or heat-resistant gloves when handlinghot objects and liquids. Students shouldwear safety goggles and lab aprons andshould not stir with the thermometers.

Teaching Tips• Students may need some guidance in

using the specific-heat equation.

Questioning Strategies Ask studentsthe following questions. Why is it impor-tant to quickly transfer the bolts intothe beaker? (Because the bolts are veryhot, they will lose thermal energy veryquickly as soon as they leave the hotwater.) Why is it important to swirl the water after adding the hot bolts?(This ensures an even temperature andmore accurate results.)

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Expected Outcome Students should measure aspecific heat for the steel can that is close to that ofthe steel bolts.

Sample Data Ten bolts with a mass of 100 g willraise the temperature of 200 mL of water by about5°C. The same mass of aluminum nails will raisethe temperature by about 9°C.

Analyze and Conclude1. The specific heat of aluminum (about 0.90 J/g•°C) is higher than the specific heat ofsteel (about 0.45 J/g•°C).

2. The specific heat of the can was very close tothe specific heat of steel. This is evidence that thecan is made mostly of steel.3. The observations support the idea that the can is made of steel, but do not prove it; other metalsmay have similar specific heats. A list of the specificheats of various metals for comparison would behelpful, as would other kinds of evidence, such asthe densities and chemical properties of the metals.4. The specific heat of the can is close to that ofsteel, suggesting that the can is primarily steel.Logical

Probeware Lab ManualVersions of this lab for use with probeware available fromPasco, Texas Instruments, andVernier are in the ProbewareLab Manual.



section 16.1 16.1 thermal energy and matter -...

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