Energy is whatever can be efficiently converted into heat or motion to provide powder to run machines and vehicles and to supply heat and light.

Energy sources are of two types, renewable and nonrenewable. Most of the industrial world is presently powered by nonrenewable fossil fuels – coal, petroleum and Natural gas – that once used, cannot be replaced. Fission nuclear reactors are fueled by uranium or plutonium, themselves finite energy sources. Spent uranium, however, can be converted to fissile plutonium in a breeder reactor, a process that makes nuclear energy almost infinitely renewable.

Nuclear technology, however, has not yet developed either failproof reactors or a safe method for disposing of nuclear wastes. The development of nuclear fusion (whose end products are harmless) has so far been hindered by the difficulties of containing the fuels (plentiful light elements such as hydrogen) at the extremely high temperatures necessary to initiate and sustain fusion.

Renewable energy sources include the energy from water and wind (i.e. Turbines, windmills and waterwheels); geothermal energy, the earth's internal heat that is released naturally in geysers and volcanoes.