Energy can be classified into two categories:
Kinetic energy which is the energy possessed by a body in motion. It is expressed mathematically as:

where m = mass of object and v = velocity
Potential energy which is the energy content of a body relative to its position. It can be expressed as:

where m = mass, g = acceleration due to gravity, h = height
The two forms of energy can be interconverted. In the given example:
A soap box derby car at the top of a ramp has potential energy and at the finish line at the bottom of the ramp it has kinetic energy.