Using Energy and Heat
Using Energy and Heat Energy Transfers and Transformations Key Concepts What do you think? Read the two statements below and decide whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you’ve read this lesson, reread the statements to see if you have changed your mind. Before
Statement
After
3. In most systems, no energy is transferred to
• What is the law of conservation of energy? • How is energy transformed and transferred? • What are renewable and nonrenewable energy resources?
the environment. 4. Some forms of energy are replenished naturally.
3TUDY#OACH
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Law of Conservation of Energy The law of conservation of energy says that energy can be transformed from one form to another, but it cannot be created or destroyed. In the flashlight below, chemical energy of the battery is transformed to electric energy that moves through the contact strip to the bulb. The electric energy is transformed into radiant energy and thermal energy in the lightbulb. The law of conservation of energy states that the amount of radiant energy shining out of the flashlight cannot be greater than the chemical energy in the battery.
Identify the Main Ideas Write one sentence to summarize the main idea in each paragraph. Write the main ideas on a sheet of paper or in your notebook to study later.
Visual Check
1. Trace the flow of energy from the batteries to the bulb.
Flashlight Cutaway Contact strip usually copper or brass, carries current through the battery
On/off switch completes the electric connection when turned on
e–
Bulb electric energy converted to radiant energy (light) and thermal energy
e– e– e–
e–
e– e–
Batteries stored chemical energy
Reading Essentials
C352_007_013_RE_L2_889408.indd 7
Using Energy and Heat
209
3/8/10 11:20:36 AM
Key Concept Check
2. Explain What is the law of conservation of energy?
Efficiency The amount of radiant energy given off by a flashlight is less than the chemical energy in the battery. Where is the missing energy? In this lesson, you will learn that in every energy transformation, some energy transfers to the environment.
Energy Transfer When a tennis player hits a ball with her racket, the mechanical energy of the racket changes the movement of the ball. The mechanical energy of the ball increases after it is hit. When energy moves from one object to another without changing form, an energy transfer occurs. The tennis racket transfers mechanical energy to the tennis ball.
Energy Transformation Key Concept Check
3. Identify an energy transfer and an energy transformation that occur when someone plays a guitar.
Where does the mechanical energy in the tennis player’s racket come from? Chemical energy stored in the player’s muscles changes to mechanical energy when she swings her arm. When one form of energy is converted to another form of energy, an energy transformation occurs.
Energy and Work
Suppose the tennis player is standing still before she serves the ball. She is using her muscles to hold the ball. Is she doing work on the ball? No. She is not doing work because the ball is not moving. If a force does not make an object move in the direction of the force, it does no work on the object.
Inefficiency of Energy Transformations
N Re onre sou new rce ab s le
R Re ene sou wa rc ble es
Make a two-tab book to explain renewable and nonrenewable resources.
210
Using Energy and Heat
C352_007_013_RE_L2_889408.indd 8
When a tennis player hits a ball with a racket, most of the mechanical energy of the racket transfers to the ball, but not all of it. You know when a ball hits a racket because you can hear a sound. Some of the mechanical energy of the racket is transformed to sound energy. In addition, some of the mechanical energy of the racket is transformed to thermal energy. The temperature of the racket, the ball, and the air surrounding both objects increases slightly. Anytime an energy transformation or an energy transfer takes place, some energy is transformed into thermal energy.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Work is the transfer of energy that occurs when a force makes an object move in the direction of the force. Work is only being done while the force is acting on the object. As the tennis player swings the racket, the racket applies a force to the ball for about 1 m. Although the ball moves 10 m, work is done by the racket only as the racket applies a force to the ball. When the ball separates from the racket, the racket no longer does work.
Reading Essentials
3/8/10 11:20:40 AM
Inefficiency in a Flashlight Recall the flashlight at the beginning of the lesson. The transformation of chemical energy of the battery to radiant energy from the lightbulb is inefficient, too. As the electric energy moves through the circuit, some electric energy transforms to thermal energy. When electric energy transforms to radiant energy in the lightbulb, more energy transforms to thermal energy. In some flashlights, the bulb is warm to the touch.
4. Identify What form of energy in a flashlight is considered to be useful energy?
Inefficiency Defined The law of conservation of energy says that energy cannot be created or destroyed. When scientists say that energy transformations are inefficient, they do not mean that energy is destroyed. Energy transformations are inefficient because not all the energy that is transformed to another form of energy is usable.
Open Systems In Lesson 1, you read that scientists often study the energy of systems. A car is a system. The chemical energy of the fuel is transformed to mechanical energy of the moving car. Because energy transformations are inefficient, some of the chemical energy transforms to thermal energy and sound energy, which are then released to the environment. An open system, such as a car engine, is a system that exchanges matter or energy with the environment.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Closed Systems Can you think of a system that does not exchange energy with the environment? What about a flashlight? You have read that a flashlight releases radiant energy and thermal energy into the environment. What about your body? You eat food, which contains chemical energy and comes from the environment. Your body also releases several types of energy into the environment, including thermal energy, mechanical energy, and sound energy. A closed system is a system that does not exchange matter or energy with the environment. In reality, there are no closed systems. Every physical system transfers some energy to or from its environment. Scientists use the idea of a closed system to study and model the movement of energy.
Reading Essentials
C352_007_013_RE_L2_889408.indd 9
Math Skills The amount of work done on an object is calculated using the formula W = F × d, where W = work, F = the force applied to the object, and d = the distance the object moves in the direction of the force and while the force is applied. For example, a student slides a library book across a table. The student pushed on the book with a force of 8.5 newtons (N), a distance of 0.3 m. The book slides a total distance of 1 m. How much work is done on the book? W=F×d W = 8.5 N × 0.30 m = 2.55 N•m = 2.6 J Recall that the distance used to calculate work is the distance the force was applied to the object. Note: 1 N•m = 1 J, so 2.6 J of work was done on the book. 5. Calculate Work A student lifts a backpack straight up with a force of 53.5 N for a distance of 0.65 m. How much work is done on the backpack?
Using Energy and Heat
211
3/8/10 11:20:54 AM
Energy Transformations and Electric Energy You probably have heard someone say “turn off the lights, you’re wasting energy.” This form of energy is electric energy. Most appliances you use every day require electric energy. Where does this energy come from?
Renewable Energy Resources
ACADEMIC VOCABULARY resource (noun) a stock or supply of materials, money, or other assets that can be used as needed
If you think about all of the energy used in the United States, you realize that people need a lot of energy to continue living the way they do. This huge demand for energy and the desire to protect the environment has resulted in a search for renewable energy resources. A renewable energy resource is an energy resource that is replaced as fast as, or faster than, it is used. Several different kinds of renewable energy resources are available.
Solar Radiant energy from the Sun, or solar energy, is one
6. Name the element from which photovoltaic cells are made.
In some solar energy plants, radiant energy from the Sun is transformed into thermal energy. The thermal energy is used to convert water to steam. The steam turns a generator, which transforms mechanical energy into electric energy.
Wind Have you ever driven along a highway and seen wind
Reading Check
7. State What energy transformations occur in a wind turbine?
212
Using Energy and Heat
C352_007_013_RE_L2_889408.indd 10
turbines? Wind turbines are built in places where winds blow almost continuously, such as the vast open spaces of the southwestern United States. Wind moves the blades of the turbine, turning a generator that transforms kinetic energy of the wind to electric energy. One of the drawbacks of wind energy is that wind does not blow steadily at all times. This source of electric energy is not very consistent or predictable.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Reading Check
energy resource that can be converted into electric energy. Some solar energy plants transform radiant energy into electric energy with using photovoltaic (foh toh vohl TAY ihk), or solar, cells. Photovoltaic cells are made from thin wafers of the element silicon. When radiant energy from the Sun hits the cells, it knocks electrons away from the silicon atoms. This movement of electrons is electric energy. Some homes, businesses, and small appliances such as calculators use photovoltaic cells to provide electricity.
Reading Essentials
3/8/10 11:20:55 AM
Hydroelectric In hydroelectric plants, falling water from rivers and dams is channeled through a turbine. When the turbine spins, mechanical energy is transformed to electric energy. Most of the hydroelectric energy produced in the United States comes from the western part of the country. One drawback of hydroelectric energy is that dams and turbines can interrupt the natural movements of animals in rivers and lakes. The number of places where rivers are large enough for these energy plants to be built is also limited.
Geothermal Earth’s temperature increases with depth below Earth’s surface. But in a few places, Earth is hot close to the surface. Geothermal plants are built where thermal energy from Earth is near Earth’s surface. These plants transfer thermal energy to water, which creates steam. The steam turns turbines in electric generators. The states with the most geothermal reservoirs are Alaska, Hawaii, and California.
Reading Check
8. State What are some drawbacks of hydroelectric plants?
Biomass Biomass includes wood, plants, and even manure
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
and garbage. All of these sources of stored chemical energy can be transformed to electric energy in energy plants. Burning biomass releases carbon dioxide into the atmosphere. Some scientists believe this contributes to climate change and global warming. However, when biomass crops are grown, the plants use carbon dioxide during photosynthesis. This reduces the overall amount of carbon dioxide from the process.
Reading Check
9. Describe how biomass
Nonrenewable Energy Resources Most of the energy used in homes, schools, stores, and businesses comes from fossil fuels and nuclear energy, as shown below. Fossil fuels and nuclear energy are nonrenewable energy resources—energy resources that are available in limited amounts or that are used faster than they can be replaced in nature.
uses carbon dioxide.
Electric Energy Net Generation by Resources as of 2007 Nonrenewable Resources
Renewable Resources
Resource
Percentage
Resource
Percentage
petroleum
1.6
biomass
about 1.0
natural gas
21.6
hydroelectric
5.8
coal
48.5
geothermal
Statement
After
3. In most systems, no energy is transferred to
• What is the law of conservation of energy? • How is energy transformed and transferred? • What are renewable and nonrenewable energy resources?
the environment. 4. Some forms of energy are replenished naturally.
3TUDY#OACH
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Law of Conservation of Energy The law of conservation of energy says that energy can be transformed from one form to another, but it cannot be created or destroyed. In the flashlight below, chemical energy of the battery is transformed to electric energy that moves through the contact strip to the bulb. The electric energy is transformed into radiant energy and thermal energy in the lightbulb. The law of conservation of energy states that the amount of radiant energy shining out of the flashlight cannot be greater than the chemical energy in the battery.
Identify the Main Ideas Write one sentence to summarize the main idea in each paragraph. Write the main ideas on a sheet of paper or in your notebook to study later.
Visual Check
1. Trace the flow of energy from the batteries to the bulb.
Flashlight Cutaway Contact strip usually copper or brass, carries current through the battery
On/off switch completes the electric connection when turned on
e–
Bulb electric energy converted to radiant energy (light) and thermal energy
e– e– e–
e–
e– e–
Batteries stored chemical energy
Reading Essentials
C352_007_013_RE_L2_889408.indd 7
Using Energy and Heat
209
3/8/10 11:20:36 AM
Key Concept Check
2. Explain What is the law of conservation of energy?
Efficiency The amount of radiant energy given off by a flashlight is less than the chemical energy in the battery. Where is the missing energy? In this lesson, you will learn that in every energy transformation, some energy transfers to the environment.
Energy Transfer When a tennis player hits a ball with her racket, the mechanical energy of the racket changes the movement of the ball. The mechanical energy of the ball increases after it is hit. When energy moves from one object to another without changing form, an energy transfer occurs. The tennis racket transfers mechanical energy to the tennis ball.
Energy Transformation Key Concept Check
3. Identify an energy transfer and an energy transformation that occur when someone plays a guitar.
Where does the mechanical energy in the tennis player’s racket come from? Chemical energy stored in the player’s muscles changes to mechanical energy when she swings her arm. When one form of energy is converted to another form of energy, an energy transformation occurs.
Energy and Work
Suppose the tennis player is standing still before she serves the ball. She is using her muscles to hold the ball. Is she doing work on the ball? No. She is not doing work because the ball is not moving. If a force does not make an object move in the direction of the force, it does no work on the object.
Inefficiency of Energy Transformations
N Re onre sou new rce ab s le
R Re ene sou wa rc ble es
Make a two-tab book to explain renewable and nonrenewable resources.
210
Using Energy and Heat
C352_007_013_RE_L2_889408.indd 8
When a tennis player hits a ball with a racket, most of the mechanical energy of the racket transfers to the ball, but not all of it. You know when a ball hits a racket because you can hear a sound. Some of the mechanical energy of the racket is transformed to sound energy. In addition, some of the mechanical energy of the racket is transformed to thermal energy. The temperature of the racket, the ball, and the air surrounding both objects increases slightly. Anytime an energy transformation or an energy transfer takes place, some energy is transformed into thermal energy.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Work is the transfer of energy that occurs when a force makes an object move in the direction of the force. Work is only being done while the force is acting on the object. As the tennis player swings the racket, the racket applies a force to the ball for about 1 m. Although the ball moves 10 m, work is done by the racket only as the racket applies a force to the ball. When the ball separates from the racket, the racket no longer does work.
Reading Essentials
3/8/10 11:20:40 AM
Inefficiency in a Flashlight Recall the flashlight at the beginning of the lesson. The transformation of chemical energy of the battery to radiant energy from the lightbulb is inefficient, too. As the electric energy moves through the circuit, some electric energy transforms to thermal energy. When electric energy transforms to radiant energy in the lightbulb, more energy transforms to thermal energy. In some flashlights, the bulb is warm to the touch.
4. Identify What form of energy in a flashlight is considered to be useful energy?
Inefficiency Defined The law of conservation of energy says that energy cannot be created or destroyed. When scientists say that energy transformations are inefficient, they do not mean that energy is destroyed. Energy transformations are inefficient because not all the energy that is transformed to another form of energy is usable.
Open Systems In Lesson 1, you read that scientists often study the energy of systems. A car is a system. The chemical energy of the fuel is transformed to mechanical energy of the moving car. Because energy transformations are inefficient, some of the chemical energy transforms to thermal energy and sound energy, which are then released to the environment. An open system, such as a car engine, is a system that exchanges matter or energy with the environment.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Closed Systems Can you think of a system that does not exchange energy with the environment? What about a flashlight? You have read that a flashlight releases radiant energy and thermal energy into the environment. What about your body? You eat food, which contains chemical energy and comes from the environment. Your body also releases several types of energy into the environment, including thermal energy, mechanical energy, and sound energy. A closed system is a system that does not exchange matter or energy with the environment. In reality, there are no closed systems. Every physical system transfers some energy to or from its environment. Scientists use the idea of a closed system to study and model the movement of energy.
Reading Essentials
C352_007_013_RE_L2_889408.indd 9
Math Skills The amount of work done on an object is calculated using the formula W = F × d, where W = work, F = the force applied to the object, and d = the distance the object moves in the direction of the force and while the force is applied. For example, a student slides a library book across a table. The student pushed on the book with a force of 8.5 newtons (N), a distance of 0.3 m. The book slides a total distance of 1 m. How much work is done on the book? W=F×d W = 8.5 N × 0.30 m = 2.55 N•m = 2.6 J Recall that the distance used to calculate work is the distance the force was applied to the object. Note: 1 N•m = 1 J, so 2.6 J of work was done on the book. 5. Calculate Work A student lifts a backpack straight up with a force of 53.5 N for a distance of 0.65 m. How much work is done on the backpack?
Using Energy and Heat
211
3/8/10 11:20:54 AM
Energy Transformations and Electric Energy You probably have heard someone say “turn off the lights, you’re wasting energy.” This form of energy is electric energy. Most appliances you use every day require electric energy. Where does this energy come from?
Renewable Energy Resources
ACADEMIC VOCABULARY resource (noun) a stock or supply of materials, money, or other assets that can be used as needed
If you think about all of the energy used in the United States, you realize that people need a lot of energy to continue living the way they do. This huge demand for energy and the desire to protect the environment has resulted in a search for renewable energy resources. A renewable energy resource is an energy resource that is replaced as fast as, or faster than, it is used. Several different kinds of renewable energy resources are available.
Solar Radiant energy from the Sun, or solar energy, is one
6. Name the element from which photovoltaic cells are made.
In some solar energy plants, radiant energy from the Sun is transformed into thermal energy. The thermal energy is used to convert water to steam. The steam turns a generator, which transforms mechanical energy into electric energy.
Wind Have you ever driven along a highway and seen wind
Reading Check
7. State What energy transformations occur in a wind turbine?
212
Using Energy and Heat
C352_007_013_RE_L2_889408.indd 10
turbines? Wind turbines are built in places where winds blow almost continuously, such as the vast open spaces of the southwestern United States. Wind moves the blades of the turbine, turning a generator that transforms kinetic energy of the wind to electric energy. One of the drawbacks of wind energy is that wind does not blow steadily at all times. This source of electric energy is not very consistent or predictable.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Reading Check
energy resource that can be converted into electric energy. Some solar energy plants transform radiant energy into electric energy with using photovoltaic (foh toh vohl TAY ihk), or solar, cells. Photovoltaic cells are made from thin wafers of the element silicon. When radiant energy from the Sun hits the cells, it knocks electrons away from the silicon atoms. This movement of electrons is electric energy. Some homes, businesses, and small appliances such as calculators use photovoltaic cells to provide electricity.
Reading Essentials
3/8/10 11:20:55 AM
Hydroelectric In hydroelectric plants, falling water from rivers and dams is channeled through a turbine. When the turbine spins, mechanical energy is transformed to electric energy. Most of the hydroelectric energy produced in the United States comes from the western part of the country. One drawback of hydroelectric energy is that dams and turbines can interrupt the natural movements of animals in rivers and lakes. The number of places where rivers are large enough for these energy plants to be built is also limited.
Geothermal Earth’s temperature increases with depth below Earth’s surface. But in a few places, Earth is hot close to the surface. Geothermal plants are built where thermal energy from Earth is near Earth’s surface. These plants transfer thermal energy to water, which creates steam. The steam turns turbines in electric generators. The states with the most geothermal reservoirs are Alaska, Hawaii, and California.
Reading Check
8. State What are some drawbacks of hydroelectric plants?
Biomass Biomass includes wood, plants, and even manure
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
and garbage. All of these sources of stored chemical energy can be transformed to electric energy in energy plants. Burning biomass releases carbon dioxide into the atmosphere. Some scientists believe this contributes to climate change and global warming. However, when biomass crops are grown, the plants use carbon dioxide during photosynthesis. This reduces the overall amount of carbon dioxide from the process.
Reading Check
9. Describe how biomass
Nonrenewable Energy Resources Most of the energy used in homes, schools, stores, and businesses comes from fossil fuels and nuclear energy, as shown below. Fossil fuels and nuclear energy are nonrenewable energy resources—energy resources that are available in limited amounts or that are used faster than they can be replaced in nature.
uses carbon dioxide.
Electric Energy Net Generation by Resources as of 2007 Nonrenewable Resources
Renewable Resources
Resource
Percentage
Resource
Percentage
petroleum
1.6
biomass
about 1.0
natural gas
21.6
hydroelectric
5.8
coal
48.5
geothermal
