1. ENERGY

2. Where Does the Energy Go? Friction is a force that oppose motion between two surfaces that are touching. For a roller coaster car to move, energy must be used to overcome the friction between the car’s wheels and the track. As a result, not all of the car’s potential energy changes into kinetic energy and not all of the car’s kinetic energy changes back into potential energy.

4. Energy Is Conserved Within a Closed System A closed system is a group of objects that transfer energy only to each other. The Law of Conservation of Energy states that energy cannot be created or destroyed. Energy can be converted from one form to another. But all of the different forms of energy in a system always add up to the same total amount of energy.

5. Energy Is Conserved Within a Closed System The image below shows energy conservation in a light bulb.

6. No Conversion Without Thermal Energy Any time one form of energy is converted into another form, some of the original energy always gets converted into thermal energy. The thermal energy due to friction that results from energy conversions is not usually useful energy. Perpetual Motion? No Way! A perpetual motion machine is a machine that would run forever without any additional energy. But perpetual motion machines are impossible because some waste thermal energy always results from energy conversions.

7. No Conversion Without Thermal Energy Making Conversions Efficient Some systems transform energy with less loss of heat than others do. Such systems are more efficient than others are. Improving the efficiency of machines is important because greater efficiency results in less waste. If less energy is wasted, less energy is needed to operate a machine.

8. Nonrenewable Resources Nonrenewable resources cannot be replaced or are replaced much more slowly than they are used. Fossil fuels are nonrenewable energy resources that formed from the remains of organisms that lived long ago. Oil, natural gas, and coal are the most common fossil fuels.

10. Nonrenewable Resources Uses of Fossil Fuels All fossil fuels contain stored energy from the sun, which can be converted into other kinds of energy. Burning coal is a common way to generate electrical energy. Petroleum is used to make gasoline, wax, and plastics. Natural gas is often used in home heating.

11. Nonrenewable Resources Electrical Energy from Fossil Fuels Electric generators convert the chemical energy in fossil fuels into electrical energy by the process shown below.

12. Nonrenewable Resources Nuclear Energy Another way to generate electrical energy is to use nuclear energy. In a process called nuclear fission, the nucleus of a radioactive atom is split into two smaller nuclei, which releases nuclear energy. Because the supply of radioactive elements is limited, nuclear energy is a nonrenewable resource.

13. Renewable Resources Renewable resources are naturally replaced more quickly than they are used. Solar Energy Sunlight can be changed into electrical energy through solar cells. Solar cells can be used in devices such as calculators. They can also be placed on the roof of a house to provide electrical energy.

14. Renewable Resources Energy from Water The potential energy of water in a reservoir can be changed into kinetic energy as the water flows through a dam. In a hydroelectric dam, falling water turns turbines. The turbines are connected to a generator that changes kinetic energy into electrical energy.

15. Renewable Resources Wind Energy The kinetic energy of wind can turn the blades of a windmill or a wind turbine. A wind turbine changes the kinetic energy of the air into electrical energy by turning a generator.

16. Renewable Resources Geothermal Energy is thermal energy caused by the heating of Earth’s crust. This energy can be converted into electrical energy at geothermal power plants. Biomass is organic matter, such as plants, wood, and waste, that can be burned to release energy. Some countries depend on biomass for energy.

17. The Two Sides to Energy Resources All energy resources have advantages and disadvantages. Many factors determine when one energy source is a better choice than another. Choosing the Right Energy Source Energy planning in all parts of the world requires careful consideration of energy needs and the availability and responsible use of resources.