16.2 text

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. ?

Thermal Energy and Heat 479

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

L1

2

L2

L2

Reading Focus

1


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

L1

L2

Section 16.2 (continued)

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

Prep Time 10 minutes

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

Class Time 20 minutes

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

L2

L2


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.

0472_hsps09te_Ch16.qxp 4/19/07 8:40 AM Page 481

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.

482 Chapter 16

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.

482 Chapter 16

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

Class Time 10 minutes

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

L2

L2

Section 16.2 (continued)

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.

Section 16.2 Assessment

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.

L1

L2

3

L2


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.

Section 16.2 Assessment

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.

484 Chapter 16

W

S

EWintersun

N

WSummer sun

484 Chapter 16

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

L2

L2

� 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


16.2 text

Documents

Transcript of 16.2 text