Energy Transformations

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1 Benchmarks SC.A Annually Assessed (pp. 161, ): The student knows that radiation, light, and heat are forms of ; SC.B Annually Assessed (p. 166): identifies forms of and explains that they can be measured and compared; SC.B (p. 163): knows the processes by which thermal tends to flow from a system of higher temperature to a system of lower temperature. Also covers: SC.B Annually Assessed (pp ), SC.B (pp. 161, 165, 166), SC.B Annually Assessed (p. 165), SC.H Annually Assessed (p. 166), SC.H Annually Assessed (p. 161) Energy Transformations Changing Forms of Energy Chemical, thermal, radiant, and electrical are some of the forms that can have. In the world around you, is changing continually from one form to another. In fact, any time is being used, it is changed from one form to another form. These changes from one form of to another are called transformations. Work is done and changes occur when changes form. A number of changes occur as the mountain biker in Figure 8 pedals up a hill. What transformations cause these changes to occur? Tracking Energy Transformations As the mountain biker pedals, his leg muscles transform chemical into kinetic. The kinetic of his legs is transferred to the bicycle as he pedals. Some of this changes into potential as he moves up the hill. Also, his body becomes warmer as chemical is transformed into thermal by his muscles. Some of the kinetic transferred to the bicycle is transformed into thermal by the friction between the bicycle parts. Thermal is always one of the products of an transformation. The transformations that cause changes to occur all produce some thermal. Apply the law of conservation of to transformations. Identify how changes form. Describe how electric power plants produce. Changing from one form to another is what makes cars run, furnaces heat, telephones work, and plants grow. Review Vocabulary heat: thermal that moves from a higher temperature to a lower temperature New Vocabulary law of conservation of mechanical generator FCAT Vocabulary Figure 8 The chemical stored in the biker s muscles is transformed into other forms of as the biker climbs the hill. Identify three transformations that occur as the biker pedals up the hill. SECTION 2 Energy Transformations 159 Lori Adamski Peek/Stone/Getty Images

2 LA.B Topic: Energy Transformations Visit fl7.msscience.com for Web links to information about transformations that occur during different activities and processes. Activity Choose an activity or process and make a graph showing how the kinetic and potential change during it. The Law of Conservation of Energy If you push a book so it slides on a table, the book slows down and stops. Was the kinetic of the book destroyed? No, it was changed to thermal by friction between the table and the book. According to the law of conservation of, can never be created nor destroyed, but only can be changed from one form to another. In any transformation, the total amount of before and after the transformation is the same. Why can t ever be lost? Changing Kinetic and Potential Energy What transformations occur when you toss a ball in the air, as in Figure 9? When the ball leaves your hand it has kinetic and potential. But as the ball moves upward it slows down. Its kinetic decreases and its potential increases. Kinetic is being transformed into potential. When the ball falls potential is converted into kinetic as the ball speeds up. However, as the ball rises and falls, the sum of the ball s kinetic and potential doesn t change. The mechanical of an object is the sum of the object s potential and kinetic. The mechanical of the ball stayed constant as it rose and fell. However, friction can cause the mechanical of an object to decrease. When the book slid across the table, friction changed the book s kinetic into thermal. As a result, mechanical was converted into thermal. Energy was changed from one form into another. Potential Figure 9 As the ball rises and falls, potential and kinetic are being converted into each other. Determine the kinetic of the ball at the point where its kinetic is the smallest. Kinetic Kinetic 160 CHAPTER 6 Richard Hutchings

3 Thermal produced by burning fuel makes the engine and coolant hot. Hot gases in the car s exhaust contain thermal produced by burning fuel. Figure 10 A car converts most of the chemical stored in gasoline to thermal that is not useful. Only a small percentage of the chemical in gasoline is converted into the kinetic of the moving car. Friction between the tires and the road converts mechanical to thermal. Using Energy Energy is used when it is changed from one form to another to perform a useful task. For example, a car transforms the chemical stored in gasoline into kinetic. However, not all of the stored in the fuel is converted into useful kinetic. Chemical is converted into thermal when the fuel is burned. Some of this thermal spreads out into the surrounding air, as shown in Figure 10. Energy Changes and Efficiency Thermal that has been spread out is no longer useful. In transformations, some always is converted into thermal that is no longer useful. This thermal is waste thermal. When is transformed, the initial amount of is converted into useful plus waste thermal. As a result, the amount of useful is always less than the initial amount of. This means that transformations are never 100 percent efficient in converting a form of into useful. FOCUS FCAT Annually Assessed Benchmark Check SC.B A ball that has 20 J of potential is dropped. What is the maximum amount of kinetic the ball could have before it hits the ground? Using Chemical Energy Inside your body, chemical also is transformed into kinetic. Look at Figure 11. The transformation of chemical to kinetic occurs in muscle cells. There, chemical reactions take place that cause certain molecules to change shape. Your muscle contracts when many of these changes occur, and a part of your body moves. The stored in food originally came from the Sun. During photosynthesis, green plants use radiant from the Sun to produce chemical compounds. Some of these compounds are eaten by humans and other organisms as food. SECTION 2 Energy Transformations 161 Harvey Schwartz/Index Stock Imagery

4 VISUALIZING ENERGY TRANSFORMATIONS Figure 11 Paddling a raft, throwing a baseball, playing the violin your skeletal muscles make these and countless other body movements possible. Muscles work by pulling, or contracting. At the cellular level, muscle contractions are powered by reactions that transform chemical into kinetic. Biceps Triceps Energy transformations taking place in your muscles provide the power to move. Skeletal muscle Muscle fiber Many skeletal muscles are arranged in pairs that work in opposition to each other. When you bend your arm, the biceps muscle contracts, while the triceps relaxes. When you extend your arm the triceps contracts, and the biceps relaxes. Nerve fiber Bundle of muscle fibers Filament bundle Muscle fibers Skeletal muscles are made up of bundles of muscle cells, or fibers. Each fiber is composed of many bundles of muscle filaments. 162 CHAPTER 6 Muscle filaments A signal from a nerve fiber starts a chemical reaction in the muscle filament. This causes molecules in the muscle filament to gain and move. Many filaments moving together cause the muscle to contract. (tl)judy Lutz, (br)lennart Nilsson, (others)stephen R. Wagner

5 Thermal moves through the air around the pan by convection. Thermal moves through the solid metal by conduction. Figure 12 When a frying pan is heated on a stove, thermal is transferred by conduction, convection, and radiation. Radiation transfers thermal to the pan's surroundings. Using Thermal Energy All forms of can be transformed into thermal. For example, chemical is transformed into thermal when something burns. Electrical is transformed into thermal when an electric current flows in a wire. Radiant is transformed into thermal when sunlight strikes your skin and makes it feel warm. Thermal is used to heat buildings and to heat water. The thermal produced by burning fuel in an automobile engine is used to make the car move. How Thermal Energy Moves Thermal does not stay in one place. Instead, it moves from a warmer material to a colder material and spreads out. Thermal can move in three ways, as shown in Figure 12. Thermal can move by conduction, which occurs when the particles in a material transfer by colliding with each other. In a liquid or a gas, thermal can move by convection. Convection occurs when particles in the liquid or gas move from a warmer region to a cooler region. The third way is by radiation, which transfers as waves. Using Radiant Energy An transformation occurs when you get a sun tan. Radiant from the Sun is transformed into chemical in your skin, making your skin darker. Radiant is used in other ways. Visible light provides the that enables you to see. Radiant from the Sun also can be converted into electrical. X rays and gamma rays are forms of radiant that can produce images of the inside of the human body and treat some diseases such as cancer. LA.A Controlling Body Temperature Most organisms have some adaptation for controlling the amount of thermal in their bodies. Some living in cooler climates have thick fur coats that help prevent thermal from escaping, and some living in desert regions have skin that helps keep thermal out. Research some of the adaptations different organisms have for controlling the thermal in their bodies. SECTION 2 Energy Transformations 163 Macduff Everton/CORBIS

6 FCAT FOCUS Annually Assessed Benchmark Check SC.B Explain why the maximum height reached by a bouncing ball decreases after each bounce. Figure 13 A coal-burning power plant transforms the chemical in coal into electrical. List some of the other sources that power plants use. Using Electrical Energy An enormous amount of electrical is used every day in the United States. Some of this electrical is converted into radiant to provide light. Electrical also is converted into thermal to heat buildings. Electric water heaters and electric stoves also transform electrical into thermal. Electric motors convert electrical to kinetic by making objects move. For example, a fan uses an electric motor to make the fan blade move. In a stereo speaker, electrical is converted to kinetic when the speaker moves back and forth. Generating Electrical Energy An enormous amount of electrical is used every day in the United States and other countries. The electrical that is available for use at any electric outlet must be generated continually by power plants. Every power plant works on the same principle is used to turn a large generator. A generator is a device that transforms kinetic into electrical. In fossil fuel power plants, coal, oil, or natural gas is burned to boil water. As the hot water boils, the steam rushes through a turbine, which contains a set of narrowly spaced fan blades. The steam pushes on the blades and turns the turbine, which in turn rotates a shaft in the generator to produce the electrical, as shown in Figure 13. What does a generator do? Chemical in coal Thermal in water An animated version of this diagram is available at fl7.msscience.com Kinetic of steam Kinetic of turbine Electrical out of generator Coal supply Stack Steam line Turbine Generator Conveyor belt Transformer that increases voltage Boiler River or reservoir Cooling water 164 CHAPTER 6 Energy and Energy Resources

7 Organized Energy and Disorganized Energy According to the law of conservation of, can t be created or destroyed. However, in transformations the amount of useful always decreases. How is useful different from that can t be used? Useful is that is concentrated, or organized, in a certain area and does not spread out. The electrical stored in a battery and the chemical stored in food are examples of organized. Energy that can t be used is spread out and less concentrated. Energy that is spread out, like waste thermal, is disorganized. Useful is organized. Whenever an transformation occurs, some organized is converted into disorganized. This means that the total amount of disorganized in the universe is always increasing. Disorder Always Increases Just as becomes more disorganized with time, matter also becomes more disorganized or disordered. For example, when food coloring is dropped in water, as in Figure 14, the food coloring becomes more disordered as it slowly spreads out. In fact, events that occur in the universe always cause disorder to increase. Figure 14 The food coloring is concentrated into a single drop before it strikes the water. In the water, the food coloring spreads out and becomes less concentrated. Summary Changing Forms of Energy The law of conservation of states that cannot be created or destroyed; it can only change form. The Thermal When total doesn t change when an transformation occurs. is always produced in transformations. an transformation occurs, the total amount of useful decreases. Generating Electrical Energy A generator converts kinetic into electrical. Burning fossil fuels produces thermal that is used to boil water and produce steam. In a power plant, steam is used to spin a turbine which then spins an electric generator. Self Check 1. Describe the conversions between potential and kinetic that occur when you shoot a basketball at a basket. SC.B Explain whether your body gains or loses thermal if your body temperature is 37 C and the temperature around you is 25 C. SC.B Describe a process that converts chemical to thermal. 4. Think Critically A lightbulb converts 10 percent of the electrical it uses into radiant. Make a hypothesis about the other form of produced. SC.B Calculate A generator converts kinetic into electrical and thermal. How much thermal results if 1,000 J of kinetic are converted into 950 J of electrical? SC.B More Section Review fl7.msscience.com SECTION 2 Energy Transformations 165 Matt Meadows