Sample  Lesson Energy is the ability to do work Energy comes in different forms: Heat (thermal) Light (radiant) Motion (kinetic) Electrical Chemical Nuclear energy Gravitational People use energy for everything from walking to sending astronauts into space. There are two types of energy: Stored (potential) energy Working (kinetic) energy 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. Energy sources can be categorized as renewable or nonrenewable When people use electricity in their homes, the electrical power is probably generated by burning coal or natural gas, by a nuclear reaction, or by a hydroelectric plant on a river, to name just a few sources. When people fill up a car’s gasoline tank, the energy source is petroleum (gasoline) refined from crude oil and may include fuel ethanol made by growing and processing corn. Coal, natural gas, nuclear, hydropower, petroleum, and ethanol are called energy sources.