Sunshine StateSTANDARDSSC.B.1.3.1: The studentidentifies forms ofenergy and explainsthat they can be meas-ured and compared.SC.B.1.3.3: The studentknows the variousforms in which energycomes to Earth fromthe Sun (e.g., visiblelight, infrared, andmicrowave).SC.G.2.3.1: The studentknows that someresources are renew-able and others arenonrenewable.

Chapter 9: Natural Resources 313

VOCABULARYnuclear fission p. 313hydroelectric energy p. 316solar cell p. 317geothermal energy p. 318biomass p. 320hydrogen fuel cell p. 320

BEFORE, you learned

• Conservation helps peoplereduce waste and reuse natural resources

• Recycling helps people recoverand extend natural resources

NOW, you will learn

• About the benefits and costs ofnuclear power

• How renewable resources areused to generate energy

KEY CONCEPT

Energy comes from othernatural resources.

EXPLORE Nuclear Energy

How can you model splitting atoms?

PROCEDURE

Work in a small group for this activity. Draw alarge circle on a piece of paper. Set the paperon the floor or on a countertop.

Put a handful of marbles in the circle (see thephotograph). Imagine the circle is an atomand the marbles are particles in its nucleus.

Take turns shooting one marble into the others.Put the marbles back in the circle after each shot.Record your observations.

WHAT DO YOU THINK?• How many marbles were

moved by each shot?• What does this activity suggest will hap-

pen when the center of an atom is struck?

3

2

1

MATERIALS• marbles• large piece of paper• pen or marker

Nuclear power is used to produce electricity.Fossil fuels are the most commonly used sources of energy, but theyare not the only ones. The United States and many other countries use nuclear power to produce electricity. In the United States, nuclearpower plants generate about 10 percent of the total energy used.

You learned that in fossil fuel power plants, water is boiled to makesteam that turns a turbine, which drives a generator. In a nuclear powerplant, the same process happens. However, the source of energy used toheat the water is nuclear fission. In the process of thenucleus of a radioactive atom is split, forming lighter elements andreleasing a huge amount of energy.

nuclear fission,

NOTE TAKINGAs you read this section,pick a note-taking strategythat will help you list thebenefits and limits of eachtype of energy source.

314 Unit 2: Earth’s Surface

Nuclear power plants use uranium atoms as fuel. When auranium nucleus splits, it forms two smaller nuclei. It also releasestwo or three neutrons and a large amount of energy in the formof light and heat. The neutrons split other uranium nuclei in aprocess called a chain reaction. This process is similar to shootingone marble into a group of marbles. Every marble that is hit willstrike others nearby.

The power-plant diagram below shows the reactor vessel wherethe chain reaction takes place. Control rods are used to limit thereaction to provide a safe amount of energy. The chain reactioncreates enough heat to produce steam in the reactor vessel.The steam heats a coiled pipe, which is used to boil water in the heat exchanger.

Steam from the exchanger turns the turbines, which drive thegenerators that produce electricity. The steam condenses intowater and is pumped back into the heat exchanger. Water fromthe cooling tower keeps the equipment from overheating. As you

can see, nuclear power plants require an abundant water supply toproduce steam and to stay cool.

Explain how nuclear fission enables a generatorto produce electricity.

A uranium nucleus splits, forming lighter elements andreleasing neutrons and a greatdeal of energy.

neutron

uraniumnucleus

lighter elements

energy

Nuclear Power Plant

Reactorvessel: Heatfrom fuel rodsturns waterinto steam.

Heatexchanger:Steam fromreactor boilswater.

Turbine:Steam fromheat exchangerdrives turbine.

Generator: Turbinedrives the generator toproduce electricity.

Cooling tower:Water flows to coolcondenser and returnsto tower as steam.

Condenser: Steam from the turbine condensesinto water and returns to heat exchanger.

Chapter 9: Natural Resources 315

water source

reactor buildingscooling towers

turbine buildings

Splitting just one atom of uranium releases 20 million times moreenergy than does burning one molecule of natural gas. However, nuclearfission also produces radioactive waste. Radioactivity is a form of energythat can cause death and disease if living things are exposed to it longenough. Nuclear waste from a power plant will remain radioactive forthousands of years. Countries that use nuclear energy face the challengeof storing this waste safely. The storage sites must keep any radioactivityfrom escaping until the waste material becomes harmless.

check your reading Explain how fission is used to generate energy.

Renewable resources are used to produce electricity and fuel.

Moving water, wind, Earth’s internal heat, sunlight, living matter, andhydrogen are all sources of renewable energy. Unlike fossil fuels, manyof these sources of energy are in unlimited supply. They usually produceelectricity or fuel with little or no pollution. Using these clean energysources helps preserve the environment and protect human health.

So far, however, these resources cannot produce enough energy topay for the cost of developing them on a large scale. As a result, renew-able resources provide only a small percentage of the energy used in theworld. In the United States, only about 6 percent of the total energyused comes from these resources.

Scientists and engineers must improve the necessary technologiesbefore renewable resources can supply clean energy to more of theworld’s people. Imagine if everyone’s car ran on hydrogen and pro-duced only water as a byproduct. Or think of solar panels generatingenough electricity to light a major city. These visions could come truein your lifetime.

check your reading What makes renewable resources attractive as energy sources?

SIMULATIONCLASSZONE.COM

Explore how a nuclearpower plant producesenergy.

A nuclear power plantusually has three mainsections: reactor buildings,turbine buildings, andcooling towers.

316 Unit 2: Earth’s Surface

Hydroelectric Energyis electricity produced by moving water. If you

have ever stood near a waterfall or even just turned on a faucet, youhave felt the force of moving water. People can use flowing water togenerate electricity.

In most cases, a dam is built across a large river, blocking the river’sflow and creating an artificial lake, or reservoir. As the illustration belowshows, water from the lake enters the dam through intake gates andflows down a tunnel. The fast flowing water turns turbines that drivegenerators, which produce electricity. Because hydroelectric power doesnot burn any fuel, it produces no pollution. Dams in the United Statesgenerate enough electricity to save 500 million barrels of oil a year.

However, building dams poses problems for the environment.By flooding land to create reservoirs, dams destroy wildlife habitats.In some rivers, such as the Snake and Columbia rivers in the UnitedStates, dams interfere with the annual migration of salmon and otherfish. Also, areas near the end of the river may receive less water thanbefore, making it harder to raise crops and livestock.

Hydroelectric energy

reservoir river

RESOURCE CENTERCLASSZONE.COM

Learn more about thebenefits and costs ofrenewable energyresources.

What would happen if the level of thereservoir fell below the intake gate?

Areas with large rivers canuse their power to produceelectricity. The dam in thephoto was built on theYukon River in Alaska.

Hydroelectric Dam

Intake gate:Water from thereservoir entersintake gates.

Tunnel: Water flowsdownhill, increasing inspeed and force.

Generator: Turbinesdrive the generators toproduce electricity.

Turbine: The movingwater turns the turbines.

Outlet: Waterflows out of thedam.

Chapter 9: Natural Resources 317

Panels are built into arrays, whichsupply electricity through powerplants like the one shown below.

Solar EnergyOnly a small fraction of the sun’s energy falls on Earth. Yet even thisamount is huge. Every day enough energy from the sun strikes theUnited States to supply all the nation’s energy needs for one and a half years. The problem is how to use this abundant resource to produce electricity.

In an effort to solve the problem, scientists developed solar cells.A is a specially constructed sandwich of silicon and othermaterials that converts light energy to electricity. As shown in the diagram below, when sunlight strikes the cell, electrons move from the lower to the upper layer, producing an electric current. Individualsolar cells can power small appliances, such as calculators and lights.

Solar cells can be wired together in solar panels, which provide heatand electricity for homes and businesses. Solar panels are also used topower some spacecraft and space stations once they are in orbit. To meetthe energy needs of some cities, hundreds or even thousands of solarpanels are built into large structures called arrays. Many western citieslike Barstow, California, receive part of their electricity from solar arrays.

Sunlight is an unlimited source of clean energy. But current methodsof collecting sunlight are expensive and somewhat inefficient. As solartechnology improves, sunlight is likely to become an important energysource for the world.

check your reading How can people use sunlight to produce electricity?

solar cell

reading tip

Array refers to an arrangement of objects in rows and columns.

VOCABULARYAdd a four-square diagramfor the term solar cell inyour notebook.

Solar cells, wired into panels,produce more current.

power plant station

Sunlight strikes a solar cell, andelectrons move to produce anelectric current.

solar arrays

318 Unit 2: Earth’s Surface

How is this plant similar to a nuclearpower plant? How is it different?

Geothermal Power Plant

Geothermal EnergyImagine tapping into Earth’s heat to obtain electricity for your home.In some places, that is exactly what people do. They use

or energy produced by heat within Earth’s crust.

Geothermal energy comes from underground water that is heatedby hot rock. The illustration below shows how hot water is piped froma well into a power plant. This superheated water enters a flash tankand produces enough steam to run turbines, which power generators.Excess water is then pumped back into the ground. Some plants alsopipe hot water into homes and businesses for heating.

In the United States, geothermal energy provides electricity fornearly 3.5 million homes. Other major geothermal power plants are in New Zealand and Iceland.

Geothermal energy is clean and renewable. So far, its use is limitedto areas where hot water is fairly close to the surface. However, somecompanies are experimenting with pumping cold water into under-ground areas of hot rock found in all parts of Earth’s crust. The rockheats the water, which is then pumped back to the surface and used

energy,

geothermal

In Iceland, geothermalpower plants like the one in the photographsupply nearly all of thecountry’s electricity.

reading tip

Geothermal combines theGreek prefix geo-, meaning“earth,” and the Greek wordtherme-, meaning “heat.”

Productionwell: Hotwater is pipedfrom theground intothe plant.

Flash tank: Water ischanged into steam.

Turbine and generator:Steam turns turbines, which drivegenerators to produce electricity.

Cooling tower:Water from thetower cools steamin the condenser.

Condenser:Steam condensesinto water.

Injection well:Excess water is pumpedback into the ground.

Chapter 9: Natural Resources 319

The blades turn the gears, which drive thegenerator to produce electricity. The controllerpoints the windmill’s head into the wind tokeep the blades turning rapidly.

blade

gears

controller

generator

reminder

The generator is the partthat produces the electriccurrent, whether it is drivenby turbines or gears.

to generate electricity. This new technique may allow more countriesto make use of geothermal energy.

check your reading What is the source of geothermal energy?

Wind EnergyFor thousands of years, people have captured the tremendous energy ofwind to move ships, grind grain, and pump water from underground.Today, people also use wind energy—from the force of moving air—to generate electricity.

The modern windmill is made of metal and plastic and can stand astall as a 40-story building. The blades act as a turbine, turning a set ofgears that drives the generator. The amount of electricity a windmillproduces depends on the speed and angle of the wind across its blades.The faster the blades turn, the more power the windmill produces.

To supply electricity to an area, hundreds of windmills are built ona “wind farm.” Wind farms, like the one in the photograph below, arealready producing electricity in California, Hawaii, New Hampshire, andseveral other states. Other countries, such as Denmark and Germany,also use wind farms to supply electricity to some of their cities.

Although wind energy is clean and renewable, it has certain draw-backs. It depends on steady, strong winds blowing most of the time,which are found only in a few places. Wind farms take up a great dealof land, and the turning blades can be noisy. There is also a limit tohow much power each windmill can produce. However, in the future,wind farms may become more productive and more widely used.

check your reading What factor determines how much electricity a windmill produces?

reminder

Keep in mind that usefulenergy is lost as heat energyin every energy conversion,as you learned in grade 6.

Content ReviewFLORIDA

Biomass Energyis organic matter, such as plant and animal waste, that can be

used as fuel. The U.S. Department of Energy works with state and localgroups to find ways of converting biomass materials into energy sources.

Each year biomass power stations in the United Statesburn about 60 million tons of wood and other plantmaterial to generate 37 billion kilowatt hours of electricity.That is more electricity than the state of Colorado uses in an entire year. Small biomass stations are used in ruralareas to supply power to farms and towns. Fast-growingtrees, grasses, and other crops can be planted to supply arenewable energy source that is cheaper than fossil fuels.

Some plant and animal waste can be converted intoliquid fuels. The sugar and starch in corn and potatoes,for example, are made into a liquid fuel called ethanol.Ethanol can be added to gasoline to form gasohol.This fuel can power small cars, farm machinery, and buses.A liquid fuel made from animal waste is used for heatingand cooking in many rural areas around the world.

Although biomass is a renewable resource, certain problems limitits use. Burning wood and crops can release as much carbon dioxideinto the air as burning fossil fuels does. Biomass crops take up land thatcould be used to raise food. Also, plant fuels such as ethanol are stilltoo expensive to produce on a large scale. For now, biomass materialsprovide only a small part of the world’s energy.

check your reading What are the advantages and disadvantages of biomass fuels?

Hydrogen Fuel CellsScientists are also exploring the use of hydrogen gas as a renewableenergy source. Hydrogen is the simplest atom, made up of one proton—the nucleus—and one electron. Scientists have found ways toseparate hydrogen from water and from fossil fuels. It is a flammablegas and must be handled with care

Hydrogen is used in a a device that produceselectricity by separating hydrogen into protons and electrons. The diagram on page 321 shows hydrogen fuel entering on one side of thecell while oxygen from the air enters on the other side. Once in the cell,electrons flow out of the cell through wires, forming an electric currentthat powers the motor. The protons pass through a membrane andcombine with oxygen to form water as a byproduct.

Hydrogen fuel cells are used to supply electrical energy on spacecraftand space stations. Fuel-cell buses are being tested in several countries.

hydrogen fuel cell,

Biomass

320 Unit 2: Earth’s Surface

This wood-burningbiomass plant sends electrical energy at a rate of 21 million watts to the San Francisco Bayarea. Wood waste prod-ucts are collected fromfarms and industries asfuel for the plant.

VISUALIZATIONCLASSZONE.COM

Watch a hydrogen fuelcell in action.

Chapter 9: Natural Resources 321

KEY CONCEPTS1. List the main advantages

and disadvantages of nuclearenergy as a power source.

2. Describe the advantages ofusing sunlight, water, andEarth’s heat energy to produceelectrical power.

3. What are some factors that limitthe use of biomass, wind, andhydrogen as energy sources?

CRITICAL THINKING4. Evaluate Do you think people

would use a clean, renewablefuel that cost twice as much asgasoline? Explain.

5. Calculate One acre of cornyields 20 gallons of ethanol. A bus gets 20 miles per gallonand travels 9000 miles in oneyear. How many acres of cornare needed to fuel the bus fora year?

CHALLENGE6. Synthesize Review the energy

sources discussed in this section.Then think of ways in whichone or more of them could beused to supply electricity to ahouse in Florida and a house in Alaska. Which energysources would be suitable ineach environment? Describeyour ideas in writing, or makesketches of the houses.

Also, some fuel-cell cars are now available to the public. Storage tanksin these vehicles carry hydrogen fuel for the cells.

Fuel-cell technology holds great promise for the future. Hydrogenis a clean source of energy, producing only water and heat as byproducts.If every vehicle in the world were powered by hydrogen, the level ofair pollution would drop sharply.

However, hydrogen fuel cells are still too expensive to produce inlarge numbers. Separating hydrogen from water or from fossil fuelstakes a great deal of energy, time, and money. Also, there are only a fewfueling stations to supply cars and other vehicles that run on hydrogen.The U.S. Department of Energy is working with the automotive industryand other industries to solve these problems.

check your reading Why is hydrogen considered a promising alternative energy source?

hydrogen

to motor

oxygen

Electrons create acurrent that runsthe motor.

Hydrogenseparates intoprotons andelectrons.

Only protons passthrough the membrane.

The protons combinewith oxygen to formwater.

A storage tank in theback of this SUV holdshydrogen fuel. Electricalenergy from fuel cellspowers the motor and a backup battery.