Energy is the ability to do some work.  It takes energy to move an object from one place to another, to walk or even heat our food. Energy is everywhere.  A fuel is a type of stored energy. Burning fuels releases stored chemical energy, which becomes useful thermal energy.

There are three categories of fuel, nonrenewable, renewable and inexhaustible. Fossil fuels such as oil, coal and natural gas are nonrenewable energy sources we commonly use. They’re made from animal and plants that lived and died in oceans and swamps millions of years ago. Eventually the decayed animal and plants turned into oil, coal and natural gas fossil fuels. Because it takes millions of years for fossil fuels to form, these sources of fuels are called nonrenewable which means it’s not possible for us to create them in a way that would make them ready for us to use soon.

The second category of fuel is called renewable, which means we can replace the resource at the same rate we consume, or use it. Biomass is an example of renewable energy source. Biomass is any material that was recently living or made from organic, or living materials that can be burned. Examples of Biomass are wood, paper, and crop waste. Biomass is readily available. The third category of energy sources like the sun, moving wind, or daily motion of the ocean waves are called inexhaustible. We can collect and use energy from these sources all the time without ever using them up. However, it is often very expensive to make collectors of energy from inexhaustible sources and we cannot always get it where we need it.