Energy is the ability to do work
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. We use energy for a variety of things, such as walking and bicycling, moving cars along roads and boats through water, cooking and refrigerating food, lighting our homes and offices, manufacturing products, and even sending astronauts into space.
There are many forms of energy:
- Heat
- Light
- Motion
- Electrical
- Chemical
- Gravitational
Energy is grouped into two general categories for doing work:
- Potential, or stored, energy
- Kinetic, or working, energy
Energy can be converted from one form to another. For example, the food you eat contains chemical energy, and your body stores this energy until you use 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 can be converted to light and heat.
Energy sources are renewable or nonrenewable
The many different sources of energy can all be divided into two categories:
- Renewable
- Nonrenewable
Renewable and nonrenewable energy sources can be used as primary energy sources to produce useful energy such as heat, or they can be used to produce secondary energy sources such as electricity and hydrogen.