There are different kinds of potential energy, but they all represent a stored energy within an object (like a rubber band), field (the Earth’s gravitational field) or system (a fire).

• A rubber band demonstrates elastic potential energy when it is stretched to its snapping point; one moment its almost motionless, the next it moves fast enough to sting your hands.
  

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• The Earth’s gravitational field demonstrates gravitational potential energy when an asteroid passes by; the asteroid is pulled down to the surface and gains so much speed that it will create a giant crater when it hits the ground.
  

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• A fire demonstrates chemical potential energy when oxygen molecules combine with the hydrocarbons in the fuel to create new molecules and give off heat and light.
  

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A compressed spring is a simple example of the exchange between different types of energy, namely elastic potential energy and kinetic energy. Both of these are in a class called mechanical energy, which generally includes all forms of energy that can do work.

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• In the first frame, the spring is not compressed or stretched, and the block is not moving. There is no mechanical energy in the system yet.
• In the second frame, the spring is compressed by the block. Neither the spring or block is moving, but the compression of the spring represents potential energy.
• When the block and spring are released in the third frame, they go from having no motion to having some motion. This kinetic energy comes from the stored potential energy of the spring.

An object dropped from a height above the ground:

• If you hold an object (like a ball) above the ground in your hand, the ball is not moving. Therefore it has no kinetic energy. Once you release the ball, it rapidly starts moving towards the ground. Where does this kinetic energy come from? It comes from a stored gravitational potential energy
  

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