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 homes and offices, to manufacture products, and to send astronauts into space.

There are many different forms of energy, including

Heat       Light       Motion       Electrical       Chemical       Gravitational

These forms of energy can be grouped into two general types of energy for doing work:

Potential or stored energy   or   Kinetic or working energy

There are many different sources of energy, which can be divided into two basic categories:

Renewable energy sources that can be easily replenished   or   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 be used to produce secondary energy sources such as electricity and hydrogen. (Source: U.S. Energy Information Administration)

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