chapter 32 Energy and Energy Resources section 1 What is energy? PS 4.1d: Different forms of energy include heat, light, electrical, mechanical, sound, nuclear, and chemical. Energy is transformed in many ways. 4.1e: Energy can be considered to be either kinetic energy, which is the energy of motion, or potential energy, which depends on relative position. Before You Read What does the phrase She has a lot of energy mean to you? What You ll Learn what energy is the difference between kinetic energy and potential energy the different forms of energy Read to Learn The Nature of Energy Energy is the ability to cause change. An object that has energy can make things happen. Look around you. Changes are happening. Someone might be walking by. Sunshine might be warming your desk. Maybe you can see the wind move the leaves on a tree. What changes are happening? When is energy noticed? You have a lot of energy. So does everything around you. But you only notice this energy when a change takes place. When a change happens, energy moves from one object to another. Energy from sunlight moves to the spot on the desktop and makes it warm. Energy from the wind moves to leaves. All objects, including desktops and leaves, have energy. Energy of Motion Things that move can cause change. Suppose a bowling ball rolls down the alley and knocks down some bowling pins. Does this involve energy? A change happens when the pins fall over. The bowling ball causes this change. Since energy is the ability to cause change, the bowling ball has energy. The energy in the movement of the bowling ball makes the pins fall. The energy an object has because of its motion is kinetic energy. So as a bowling ball moves,it has kinetic energy.if an object is not moving, it does not have kinetic energy. Highlight Forms of Energy As you read this section, highlight the different forms of energy. Then write an example of each type of energy next to the places you highlighted. A Organize Information Make the following Foldable to organize information about the nature of energy, the energy of position, and the different forms of energy. Reading Essentials 21
1. Apply Does a slowermoving object have more or less kinetic energy than a faster-moving object? B Compare and Contrast Make the following Foldable to compare and contrast kinetic energy and potential energy. Picture This 2. Determine Which vase on the shelves has the most potential energy? How are kinetic energy and speed related? What would happen to the bowling pins if the bowling ball rolls faster? More of the pins might fall down or they might move farther. A faster bowling ball causes more change to happen than a slower bowling ball. The faster the bowling ball goes, the more kinetic energy it has. This is true for all moving objects. Kinetic energy increases as an object moves faster. How are kinetic energy and mass related? Suppose you roll a volleyball down the alley at the same speed as a bowling ball. Will the volleyball move the pins as far as the bowling ball will? The answer is no. The volleyball might not knock down any pins. How are the volleyball and the bowling ball different? They are moving at the same speed, but the volleyball has less mass. The volleyball has less kinetic energy than the bowling ball because it has less mass. Kinetic energy increases as the mass of an object increases. Energy of Position An object can have energy even if it is not moving. Look at the vase on top of the bookcase. The vase does not have any kinetic energy because it is not moving. What if it accidentally falls to the floor? Changes happen. Gravity pulls the vase downward. The vase has kinetic energy as it falls. Where did this energy come from? When the vase was sitting on the shelf, it had potential (puh TEN chul) energy. Potential energy is the energy stored in an object because of its position. The position of the vase is its height above the floor. As the vase falls, the potential energy is transformed, or changed, from one form to another. It is transformed into kinetic energy. A vase has more potential energy if it is higher above the floor. Potential energy also depends on mass. The more mass an object has, the more potential energy it has. The objects in the figure have different amounts of potential energy. 22 Energy and Energy Resources
Forms of Energy Food, sunlight, and wind have energy. But they have different kinds of energy. The energy in food and sunlight is different from the kinetic energy in the wind. The warmth you feel from sunlight is different from kinetic energy or potential energy. What is thermal energy? When you sit near a sunny window, you get warm. The feeling of warmth is a sign that you are getting more thermal energy. Thermal energy is energy of an object that increases as the object s temperature increases. All objects have thermal energy. In the figure below, a cup of hot chocolate has more thermal energy than a bottle of cold water. The bottle of cold water has more thermal energy than a block of ice with the same mass. Picture This 3. Identify Circle the object with the greatest thermal energy. Put a box around the object with the least thermal energy. Your body makes thermal energy all the time. Chemical reactions that happen inside your cells make thermal energy. Where does this energy come from? Thermal energy is released by chemical reactions. Thermal energy comes from another kind of energy called chemical energy. What is chemical energy? Chemical energy is the energy stored in chemical bonds. Some of this energy is released when chemicals are broken apart and new chemicals are made. For example, food has chemical energy that your body uses to help you think, move, and grow. Food has chemicals, such as sugar. The chemicals are made of atoms that are bonded together. Energy is stored in the bonds between atoms. These chemical bonds can be broken down in your body to release energy. Also, the flame of a candle comes from chemical energy stored in wax. When the wax burns, chemical energy changes into thermal energy and light energy. 4. Explain What has stored chemical energy that your body uses? Reading Essentials 23
5. Summarize When does light energy change to thermal energy? 6. Compare Which of the following can carry the most current? a. 9-V battery b. 220-V electrical outlet c. 12-V battery d. 110-V electrical outlet What is radiant energy? Light from the candle flame travels very fast through the air. It moves at a speed of 300,000 km/s. This is fast enough to circle Earth almost eight times in 1 s. When light hits an object, three things can happen. The light can be absorbed by the object, reflected by the object, or be passed through the object. When an object absorbs light energy, the object can get warmer. The light energy changes into thermal energy. You can feel this happening if you wear a black shirt outside on a sunny day. The energy carried by light is radiant energy. You can use electrical energy to make radiant energy. Imagine a metal heating coil on an electric stovetop. As it is heated, it becomes red hot. The hotter it gets, the more radiant energy it gives off. Electrical energy is being used to make the heating coil warmer. What is electrical energy? Electrical energy is used in many ways. Electrical energy is carried by the electric current that comes out of batteries and electrical outlets. Electrical lighting uses electrical energy. Look around at all the devices that use electrical energy. The amount of electrical energy depends on the voltage. The current out of a 120-V electrical outlet can carry more energy than the current out of a 1.5-V battery. Large power plants are needed to make the huge amount of electrical energy people use every day. About 20 percent of the electrical energy made in the United States comes from nuclear power plants. What is nuclear energy? Nuclear power plants use the energy stored in the nucleus of an atom to make electricity. Nuclear energy is the energy in the nucleus of every atom. Nuclear energy can be transformed into other kinds of energy. Releasing nuclear energy is difficult. Complicated power plants are necessary to produce nuclear energy. Releasing nuclear energy from an atom is very different from releasing chemical energy from wood. To do that, all you need is a lighted match. 24 Energy and Energy Resources
After You Read Mini Glossary chemical energy: the energy stored in chemical bonds electrical energy: the energy carried by the electric current that comes out of batteries and electrical outlets energy: the ability to cause change kinetic energy: the energy an object has because of its motion nuclear energy: the energy in the nucleus of every atom. potential energy: the energy stored in an object because of its position radiant energy: the energy carried by light thermal energy: the energy of an object that increases as temperature increases 1. Read the key terms and definitions in the Mini Glossary above. On the lines below, explain the difference between the terms potential energy and kinetic energy. 2. Match the forms of energy with the correct examples. Write the letter of each example in Column 2 on the line in front of the form of energy it matches in Column 1. Column 1 Column 2 1. potential energy a. the energy that makes a television work 2. kinetic energy b. a lamp giving off light 3. electrical energy c. the energy in food 4. thermal energy d. a ball rolling 5. chemical energy e. a book sitting on a shelf 6. nuclear energy f. the energy in a cup of hot tea 7. radiant energy g. the energy in an atom s nucleus 3. You were asked to highlight the different forms of energy in this section. What do you think would be another way to help you remember the different forms of energy? Visit glencoe.com to access your textbook, interactive games, and projects to help you learn more about energy. End of Section Reading Essentials 25
Identify Main Ideas Highlight the main point in each paragraph as you read this section. Study the main points, then state each point in your own words. C chapter 32 Describe Make the following Foldable. Inside, describe the law of conservation of energy and give examples. Law of Conservation of Energy Energy and Energy Resources section 2 Energy Transformations PS 4.1c: Most activities in everyday life involve one form of energy being transformed into another. Energy, in the form of heat, is almost always one of the products of energy transformations. 4.3a: In chemical reactions, energy is transferred into or out of a system. Light, electricity, or mechanical motion may be involved in such transfers in addition to heat. 4.4d: Electrical energy can be produced from a variety of energy sources and can be transformed into almost any other form of energy. Also covered: 4.1d, 4.1e, 4.5a, 4.5b. What You ll Learn to apply the law of conservation of energy energy changes form how electric power plants make energy Before You Read Explain how you used one kind of energy today. Read to Learn Changing Forms of Energy Energy can have different forms such as chemical, thermal, radiant, and electrical. All around you, at all times, energy is being transformed. This means it is changing from one form to another. You see some of these transformations when you notice a change in your environment. Forest fires are an example of a change involving energy. They can happen naturally because of lightning strikes. Changes also happen as a mountain biker pedals up a hill. How can you track energy transformations? A mountain biker s leg muscles transform chemical energy into kinetic energy as he pedals. The kinetic energy of his leg muscles is transformed into kinetic energy of the bicycle as he pedals. As he moves up the hill, some of this energy is transformed into potential energy. Some energy also is transformed into thermal energy. His body is warmer because chemical energy is being released. The parts of the bicycle are warmer too because of friction. When energy is transformed, heat energy usually is made. People exercising, cars running, and living things growing all produce heat. The Law of Conservation of Energy The law of conservation of energy states that energy is never created or destroyed. The only thing that changes is the form of the energy. 26 Energy and Energy Resources
When the biker is resting at the top of the hill, all of his original energy is still around. Some of his energy changed into potential energy. Some changed into thermal energy. No energy is missing. It can all be accounted for. Changing Kinetic and Potential Energy The law of conservation of energy can be used to identify energy changes in a system. For example, tossing a ball into the air and catching it is a simple system. As the ball leaves your hand, most of its energy is kinetic. As it rises, it gets slower. It loses kinetic energy. The kinetic energy is changed into potential energy. The amount of kinetic energy that it loses equals the amount of potential energy that it gains. The total amount of energy stays the same. Energy Changes Form Energy changes form all the time all around you. Many machines transform energy from one kind to another. For example, an automobile engine transforms the chemical energy in gasoline into kinetic energy. Some of the chemical energy also is transformed into thermal energy, making the engine hot. An engine that converts chemical energy into more kinetic energy and less thermal energy is a more efficient engine. New kinds of cars use an electric motor along with a gasoline engine. These engines are more efficient so the car can travel farther on a gallon of gas. How is chemical energy transformed? Chemical energy can be transformed into kinetic energy inside your body. This happens in muscle cells. Chemical reactions take place and cause certain molecules to change shape. Many of these changes make your muscles contract. This makes a part of your body move. Biomass Biomass is the matter in living organisms. Biomass contains chemical energy. When organisms die, chemical compounds in their biomass break down. Bacteria, fungi, and other organisms help change these chemical compounds into simpler chemicals. These simpler chemicals are used by other living things. Thermal energy also is released when these biomass breaks down. For example, as a compost pile decomposes, chemical energy is changed into thermal energy. The temperature of a compost pile can reach 60 C. 1. Draw Conclusions At what point does the ball have the most potential energy? a. when it reaches its highest point b. when it leaves your hand c. just before you catch the ball d. halfway up in the air 2. Summarize What kind of energy does bacteria and fungi help transform? Reading Essentials 27
How is electrical energy transformed? You use electrical energy every day. When you flip a light switch or turn on a radio, electrical energy is transformed into other forms of energy. You use electrical energy when you plug something into an electrical outlet or use a battery. Hearing Sounds The figure shows how electrical energy is transformed into other kinds of energy when you listen to a radio. A loudspeaker in the radio changes electrical energy into sound waves. The sound waves travel to your ear. This is energy in motion. The energy carried by the sound waves makes parts of your ear move too. This energy of motion is transformed into chemical and electrical energy in nerve cells. The nerve cells send the energy to your brain. Your brain figures out that the energy is a voice or music. Where does the energy go after the brain? It finally is transformed into thermal energy. Picture This 3. Identify What kind of energy travels through the air from a radio? 4. Check Understanding How can thermal energy be used to make kinetic energy? 28 Energy and Energy Resources What changes into thermal energy? Different kinds of energy can be transformed into thermal energy. When something burns, chemical energy changes into thermal energy. Electrical energy changes into thermal energy when a wire that is carrying an electrical current gets hot. Thermal energy can be used to heat buildings and keep you warm. Thermal energy also can be used to heat water. If you heat water to its boiling point, it changes to steam. Steam can be used by steam engines to make kinetic energy. Steam engines were once used on steam locomotives to pull trains. Thermal energy also can be transformed into radiant energy. This happens when you heat a metal bar until it is so hot that it glows and gives off heat.