Explain how energy is conserved within a closed system. Explain the law of conservation of energy.

Transcription

1 Section 3 Conservation of Energy Objectives Explain how energy is conserved within a closed system. Explain the law of conservation of energy. Give examples of how thermal energy is always a result of energy conversion. Explain why perpetual motion is impossible.

2 Section 3 Conservation of Energy Where Does the Energy Go / What Is It Used For? Energy on a Roller Coaster To find out where a roller coaster s original potential energy goes, you have to think about more than just the hills of the roller coaster. Friction plays a part too. Friction is a force that opposes motion between two surfaces that are touching. See how friction plays a part in roller coaster energy conversions on the next slide.

3 Section 3 Energy Conversions in a Roller Coaster

4 Section 3 Conservation of Energy Energy Is Conserved Within a Closed System What Is a Closed System? A closed system is a group of objects that transfer energy only to each other. No other energy is added to the system Law of Conservation of Energy According to the law of conservation of energy, energy cannot be created or destroyed. Energy is changed from one form to another

5 Section 3 Conservation of Energy No Conversion Without Thermal Energy Some waste thermal energy always results from energy conversions due to friction. Perpetual Motion? No Way! People have sometimes tried to make a machine that would run forever without any additional energy. This perpetual motion machine would put out exactly as much energy as it takes in. But that s impossible, because some energy always changed to thermal energy Making Conversions Efficient In terms of energy conversions, energy efficiency is a comparison of the amount of energy before a conversion with the amount of useful energy after a conversion.

6 Energy Resources Objectives Name several energy resources. Explain how the sun is the source of most energy on Earth. Evaluate the advantages and disadvantages of using various energy resources.

7 Energy Resources Nonrenewable Resources can not be replaced the source will run out Uses of Fossil Fuels Oil and natural gas, shown on the next slide, as well as coal, are the most common fossil fuels. All fossil fuels contain stored energy from the sun, which can be converted into other kinds of energy. Electrical Energy from Fossil Fuels One way to generate electrical energy is to burn fossil fuels. Nuclear Energy Another way to generate electrical energy is to use nuclear energy.

8 Formation of Fossil Fuels

9 Energy Resources Renewable Resources can be replaced, will not run out Solar Energy Sunlight can be changed into electrical energy through solar cells. Energy from Water The sun causes water to evaporate and fall again as rain that flows through rivers. The potential energy of water in a reservoir can be changed into kinetic energy as the water flows through a dam. Wind Energy A wind turbine changes the kinetic energy of the air into electrical energy by turning a generator.

10 Energy Resources Renewable Resources continued Geothermal Energy Thermal energy caused by the heating of Earth s crust is called geothermal energy. Some geothermal power plants pump water underground next to hot rock. The water returns to the surface as steam, which can then turn the turbine of a generator. Biomass Plants use and store energy from the sun. Organic matter, such as plants, wood, and waste, that can be burned to release energy is called biomass.

11 Energy Resources The Two Sides to Energy Resources Advantages and Disadvantages All energy resources have advantages and disadvantages. Choosing the Right Energy Resource Energy planning in all parts of the world requires careful consideration of energy needs and the availability and responsible use of resources. Refer to page 146 Table 1

12 Energy Resources How Electricity Is Generated From Different Energy Sources