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Physics > Potential Energy

Potential energy is the energy that an object has when in a particular position. It is sometimes referred to as gravitational potential energy because usually the object needs to be lifted into a position in order to gain this potential energy.

Imagine a person sitting on a swing. If you pull the swing back in order to start it moving, you are lifting it into a position where it gains gravitational potential energy because if you then let go, it will fall because of gravity. As it falls, this potential energy is converted into kinetic (moving) energy.

There are different types of potential energy that are associated with a particular type of force. Work of gravitational force is called gravitational potential energy (or G.P.E) energy stored in an elastic band or spring for example is called elastic potential energy. Coulomb force described electric potential energy while the work of intermolecular forces is known as intermolecular potential energy.

Factors which affect the gravitational potential energy of an object can be the height the object is raised, the strength of the gravitational field and the object’s mass. If a brick is lifted up onto a wall, as it is being moved up, it is working against gravity. When placed at the top, it has gained potential energy. Because energy cannot be destroyed, only transferred, if the brick was to fall, its gravitational potential energy would be converted into kinetic energy and when the brick hits the floor that kinetic energy would be converted into sound and heat by the impact.

The formula for calculating gravitational potential energy is:

Change in potential energy = weight x change in height

This is often expressed as:

ΔEp = mgΔh

Using this equation to work out the potential energy of a person on a swing, for example, you will need to know the weight of the person and the vertical height the person moved when the swing is pulled back. Let's say the person is 250N and the vertical height is 0.4m. We can puts those numbers into the equation below.

mgΔh = 250N x 0.4m = 100J

Note the unit for any form of energy is the Joule (abbreviated to a capital J).