Kinetic and Potential Energy Stores
The three most common energy stores are: Kinetic energy, Elastic potential energy and gravitational potential energy.
Movement means energy in an object’s kinetic energy store
- Anything that is moving has energy in its kinetic energy store. Energy is transferred to this store when an object speeds up and is transferred away from this store when an object slows down.
- The energy in the kinetic energy store depends on the object’s mass and speed. The greater the mass and the faster its going, the more energy it will have.
Formula: E=1/2mv(2)
Kinetic energy= 1/2 mass x velocity(2)
Example: A car of mass 2500kg is travelling at 20mph. Calculate the energy
(1/2 x 2500) x 20(2)=500,000Joules
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Raised objects store energy in gravitational potential energy stores
- Lifting an object in a gravitational field requires work, which causes a transfer of energy to the gravitational potential energy store of the raised object. The higher the object, the more gravitational potential energy.
- The amount of energy depends on the object’s mass, height and strength.
Formula: E= mgh
Gravitational potential energy= Mass x Gravitational Strength x Height
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Falling objects also transfer energy
When something falls, energy from its gravitational potential energy store is transferred into its kinetic energy store.
For a falling object when there’s no air resistance:
Energy lost from the g.p.e store = Energy gained in the kinetic energy store
In real life, air resistance acts against all falling objects- causing some energy to be transferred to other energy stores, e.g. thermal energy store of the objects and surroundings'.
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Stretching can transfer energy to elastic potential energy stores
Stretching or squashing an object can transfer energy to its elastic potential energy store. So long as the limit of proportionality has not been exceeded, energy in the elastic potential energy store can be found.
Formula: E=1/2ke(2)
Elastic potential energy= 1/2 spring constant x extension(2)
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