Fuels as an Energy Source

When you're out camping, you use the sun's radiant energy to see what you're doing. But what happens when you need light after the sun goes down? You produce light by using fuels you have brought along: you make a wood fire, light a kerosene lamp, or start an electrical generator fueled by gasoline. You might also use a battery-powered flashlight, but remember that a fuel was probably used to generate the electricity that charged the batteries.

A fuel is normally a chemical energy source whose energy is released for use by combustion (burning). Uranium and plutonium are the exceptions. Because uranium and plutonium also must undergo a human-controlled reaction to release nuclear energy, they are often called nuclear "fuels" even though they are not burned.