Scientists define energy as the ability to do work. Modern civilization is possible because people have learned how to change energy from one form to another and then use it to do work. People use energy to walk and bicycle, to move cars along roads and boats through water, to cook food on stoves, to make ice in freezers, to light our homes and offices, to manufacture products, and to send astronauts into space.
There are many different forms of energy, including
These forms of energy can be grouped into two general types of energy for doing work:
- Potential or stored energy
- Kinetic or working energy
Energy can be converted from one form to another. For example, the food a person eats contains chemical energy, and a person’s body stores this energy until he or she uses it as kinetic energy during work or play. The stored chemical energy in coal or natural gas and the kinetic energy of water flowing in rivers can be converted to electrical energy, which in turn can be converted to light and heat.
Energy sources can be categorized as renewable or nonrenewable
There are many different sources of energy, which can be divided into two basic categories:
- Renewable energy sources that can be easily replenished
- Nonrenewable energy sources that cannot be easily replenished
Renewable and nonrenewable energy sources can be used as primary energy sources to produce useful energy such as heat, or they can used to produce secondary energy sources such as electricity and hydrogen.