516 Lesson 1

FIGURE 1 First Flight Powered by gasoline, the Wright brothers’ plane rises above the beach at Kitty Hawk.

KItty HawK, December 17, 1903. On a windswept beach in North Carolina, a small, fragile airplane, piloted by Orville Wright, rose into the air. As his brother Wilbur held his breath, Orville managed to keep the tiny airplane aloft for 12 seconds, flying 36 meters (40 yards) across the sand. With that short flight, the Wright brothers forever changed the way people travel and transport materials. Today huge jets carry passengers and cargoes across continents and oceans.

The Wright brothers’ tiny plane and modern jets are different in many ways, but they share some characteristics. For one thing, both need fuel to fly, and the fuel they use comes from petroleum. Today’s jet is much big-ger, and travels much faster and farther, than the first airplane. Therefore, a jet uses a lot more fuel than the plane that took to the air at Kitty Hawk.

LESS

ON 1 Energy: An Overview

• Define energy and differentiate between kinetic and potential energy.

• Identify different forms of energy.• Describe how human society uses energy resources.

Reading Strategy As you read about forms of energy, make a two-column table. List the forms of energy in the left column. In the right column, take notes about each form of energy.

Vocabulary energy, kinetic energy, potential energy, combustion, energy efficiency, renewable energy, nonrenewable energy, electricity

Guiding Question: What is energy and how is it used?

17.1 Lesson PLan PreviewDifferentiated Instruction Support struggling students by giving them a visual example of potential and kinetic energy.Inquiry Students observe how various devices convert energy from one form to another.Real World Students relate energy use to the many electri-cal devices in their daily lives.

17.1 resourcesIn Your Neighborhood Activity, Home Energy Use • Lesson 17.1 Worksheets • Lesson 17.1 Assessment • Chapter 17 Overview Presentation

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What Is Energy? Energy, which is the ability to do work, can be classified as

either kinetic or potential.

Fuel supplies airplanes, big and small, with energy. Energy is the ability to do work or cause a change. Airplanes do work when they move from one place to another. Energy from the sun changes Earth by warming the atmosphere. The sun’s energy also causes a change when, in photosyn-thesis, it powers chemical reactions in which carbon dioxide and water combine to form food molecules. Energy ran the printing presses that printed this book, and energy enables you to turn these pages. And with-out energy, you couldn’t read the words in this paragraph.

Energy is necessary to change the position, composition, or tempera-ture of something. Most forms of energy fall into one of two categories—kinetic energy or potential energy.

Kinetic Energy On a bright winter day, a skier zooms down a hill. The fast-moving skier has kinetic energy. Kinetic energy is the energy that an object has due to its motion. A whizzing baseball, a train speeding down a track, a jumping frog, and a wave crashing on a beach all have kinetic energy. You can think of kinetic energy as energy in action.

Potential Energy Before the skier took off, she stood at the top of the hill. At that time, before she started moving, she had potential energy, because objects that are high up tend to go downward. Potential energy is energy that an object has because of its position or shape. In contrast to kinetic energy, potential energy is energy that is stored. A stretched rubber band has potential energy. When you release the rubber band, it jumps away from your hand. The rubber band now has kinetic energy because it is moving.

ReadingCheckpoint

What is energy?

FIGURE 2 Potential and Kinetic Energy (a) At the top of the hill, the skier has potential energy. (b) As she zooms downward, she has kinetic energy.

(b)(a)

FOCUS Start a cluster diagram on the board by writing word energy and circling it. Have students come forward to add words and phrases that describe energy or ways that energy is used. After students read the lesson, have them suggest more words and phrases to add to the diagram.

GUIDING QUESTION

ANSWERS

Reading Checkpoint The ability to do work or cause a change

518 Lesson 1

Forms of Energy Forms of energy include mechanical energy, electrical energy,

thermal energy, electromagnetic energy, chemical energy, and nuclear energy.

It’s a warm, sunny Saturday, so you and a few friends decide to hike to the top of a hill. You call your parents on your cell phone to let them know what your plans are. Then you pick up your backpack and start climbing. When you get to the hilltop, you and your friends break for lunch, and you eat the sandwich that you packed. On your hike and the lunch break that followed, you used several kinds of energy. Energy comes in many forms, and each of these forms can be converted into other forms.

Mechanical Energy The motions involved in picking up your back-pack and hiking involve mechanical energy. Mechanical energy is associ-ated with the motion and position of an object. A moving baseball has mechanical energy that is kinetic. So do a speeding bike and a car moving down a street. A compressed spring has mechanical energy that is poten-tial. When you release the spring, the stored energy becomes kinetic, and the spring moves.

Electrical Energy A cell phone uses electrical energy to send mes-sages. Electrical energy is energy associated with electric charges. Electrical energy stored in a cell phone’s battery is potential energy. When you use the phone to make a call, the energy is kinetic. Electrical energy powers many things you use, such as light bulbs, computers, DVD play-ers, and hair dryers.

Thermal Energy All materials are composed of tiny particles called atoms and molecules. These particles are moving all the time. Thermal energy is the kinetic energy of all the atoms and molecules in an object. The more energy the atoms and molecules have, the faster they move. If the particles in an object start to move faster, the object will become warmer. The particles in hot volcanic lava move very fast.

ReadingCheckpoint

What kind of energy does a compressed spring have?

FIGURE 3 Different Forms of Energy As the hikers move, they use mechanical energy. Chemical energy from food powers their muscles.

ANSWERS

Reading Checkpoint A compressed spring has mechanical energy that is potential.

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Electromagnetic Energy When the sun warms you or you cook food in a microwave oven, you are experiencing or using electromagnetic energy. Electromagnetic energy travels through space in the form of waves. Visible light is a type of electromagnetic energy, as are radio waves and ultraviolet radiation.

Chemical Energy The food you and your friends eat while hiking provides your bodies with chemical energy. Food, such as corn, is made of molecules, and chemical energy is stored in the bonds that hold the atoms together in molecules. When bonds in molecules break, energy may be released. Chemical energy is potential energy, because it is stored in chemical bonds. When you move your legs and arms during hik-ing, your body converts chemical energy stored in food into mechanical energy. Like food, fossil fuels contain energy stored in the molecules of chemical compounds.

Nuclear Energy Chemical energy involves bonds between atoms. Nuclear energy, in contrast, involves forces within atoms. The nucleus is the central part of an atom. The forces that hold nuclear particles together in the nucleus can store a huge amount of potential energy. You will learn more about nuclear energy later in this chapter.

Energy Conversion Energy can be converted, or changed, from one form to another. For example, when you turn on an electric fan, the blades of the fan turn around. In the fan’s motor, electrical energy has been converted to mechanical energy. The mechanical energy of the moving blades produces cooling breezes. When fireworks explode in the night sky, chemical energy has been converted to thermal energy and electromagnetic energy. The electromagnetic energy takes the form of the brightly colored light displays and patterns we associate with fireworks.

▶ Combustion Combustion is another example of energy conversion. Combustion is the process in which a fuel burns because it combines rapidly with oxygen. Chemical energy stored in the fuel is converted to thermal and electromagnetic energy. You feel the thermal energy as heat and see the electromagnetic energy as light.

▶ A Combustion Equation Many substances can serve as fuels. The fuels you are most familiar with are wood and fossil fuels such as coal and oil. The chemical equation for the combustion of natural gas, a fossil fuel composed mostly of methane (CH4), is shown below.

CH4 + 2O2 → CO2 + 2H2O

The principal products of the combustion of methane—and of other fossil fuels—are carbon dioxide and water. Both carbon dioxide and water vapor are greenhouse gases.

520 Lesson 1

Energy Efficiency Airplanes, cars, and fans all require energy to do the jobs they are designed to perform. However, not all the energy sup-plied is used to do the work for which it is intended. In a car, for example, some of the energy supplied by the fuel is converted to heat rather than motion. Energy efficiency is an expression of how much of the energy put into a system actually does useful work. Energy efficiency is usually expressed as a percentage. For example, if an automobile has an energy efficiency of 15 percent, only 15 percent of the energy provided by the fuel actually moves the car forward.

Sources and Uses of Energy Human society uses renewable and nonrenewable energy

resources in industry, transportation, commerce, and residences.

Highly industrialized nations such as the United States use an enormous amount of energy. Where does that energy come from, and how is the energy used?

Renewable and Nonrenewable Energy Energy resources can be divided into two broad categories: renewable energy and nonrenewable energy. Sources of renewable energy are nearly always available some-where on Earth’s surface, or they are replaced in a relatively short time. Renewable energy resources include the sun, wind, moving water, wood, and heat that comes from deep within Earth. Sources of nonrenewable energy, in contrast, cannot be replaced. Nonrenewable energy resources include fossil fuels, such as coal, oil, and natural gas, and nuclear energy. Once these resources are used up, they are gone forever.

All the renewable and nonrenewable energy resources identified above are primary energy resources. Primary energy resources are found in nature. Electricity, which is energy made available by the flow of an electric charge, is considered a secondary source of energy, because it must be produced using a primary energy resource. For example, electricity can be produced by burning coal. Electricity is useful because it can be trans-ferred over long distances and used in many ways.

2. Relate Cause and Effect After you inserted the batteries into the flashlight, what happened when you turned the switch on? Why?

3. Apply Concepts What form of energy lights a flashlight bulb?

4. Use Analogies How is a flashlight battery like a box in which you put baseball bats when they are not being used?

Where’s the Energy?21 3 4 65 7 8 9 Obtain a flashlight and remove the batteries.

21 3 4 65 7 8 9 Turn the flashlight’s switch on. Observe what happens.21 3 4 65 7 8 9 Now put the batteries back in the flashlight, and turn the

flashlight on. Observe what happens now.21 3 4 65 7 8 9 Leave the flashlight turned on. After a few minutes, put your

hand close to the bulb of the flashlight. What do you feel?Analyze and Conclude1. Infer When the flashlight did not have batteries, what hap-

pened when you switched it on? Why did this happen?

FIGURE 4 Renewable Energy Wind holds the kite aloft. Wind is a renewable energy resource.

ANSWERS

Quick Lab1. The bulb did not light because

there was no source of energy. 2. The light came on; the batteries

supplied energy.3. Electrical energy4. Both the battery and box are used

for storage. The battery stores energy; the box stores bats for future use.

Industrial31%

Residential22%

Commercial19%

Transportation28%

Source: Energy Information Administration, Annual EnergyReview 2008.

Share of Energy Consumed by Major Sectors of the Economy, 2008

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1. Compare and Contrast Contrast kinetic energy and potential energy. Give an example of each.

2. Relate Cause and Effect Carbohydrate molecules are found in foods. These carbohydrate molecules provide your body with energy. How does this happen?

3. Explain Why is electricity considered a secondary source of energy?

4. Explore the BIGQUESTION Is the energy con-tained in fossil fuels potential energy or kinetic energy? Explain your answer.

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How Energy Is Used The U.S. Department of Energy (DOE) identi-fies four general ways that energy is used in the United States. As the graph in Figure 5 shows, energy is used in industry, transportation, residences, and commerce. In industry, energy is used to accomplish jobs such as constructing buildings and making products. Transportation vehicles that use energy include cars and trucks, of course, and also boats, airplanes, trains, and even motorcycles. Residences—including your apartment or house—use electricity to run appliances, light bulbs, and electronic devices. Commercial uses occur in places where business is conducted, such as offices, supermarkets, and shopping malls.

Worldwide Patterns of Energy Use Developed nations generally use far more energy than do developing nations. Per person, nations with the most industry use up to 100 times more energy than do nations with little industry. The United States has only 4.5 percent of the world’s popu-lation; however, it consumes 21.1 percent of the world’s energy.

Developed and developing nations also tend to use energy differently. Developed nations use about two thirds of their energy on transportation and industry. In contrast, developing nations use most of their energy to provide the basic necessities of life. Such activities include farming, pre-paring food, and heating homes.

FIGURE 5 How We Use Energy The graph shows the different ways that energy is used in the United States—for industry, transportation, homes, and commerce. Notice that industry uses the highest percentage of energy.

ANSWERS

Lesson 1 Assessment1. Kinetic energy is the energy that

an object has because of its mo-tion, while potential energy is related to an object’s position or shape. Sample examples: kinetic energy—a basketball bouncing; potential energy—a basketball held above the floor.

2. Energy is released when the bonds within the carbohydrate molecules are broken down.

3. Because it is not found in nature; it must be produced using a primary energy source, such as coal

4. The energy in fossil fuels is poten-tial, because it is stored energy.