What are Kinetic Energy and Potential Energy?

In short

Kinetic energy is the energy an object has because it is moving, $\tfrac{1}{2}mv^2$ . Potential energy is the energy stored because of position or condition, for example height, $mgh$ .

In simple words

Both are measured in joules. Moving water, a rolling ball and a speeding car have kinetic energy. A book on a high shelf, a stretched spring and a charged battery have potential energy. Energy changes from one kind to the other. A falling ball loses potential energy and gains kinetic energy, and the total stays the same when there is no friction. Sunlight is radiant energy carried by moving light, so it is usually grouped with kinetic energy, while fuel, food and a charged battery store potential energy.

Example

A $2.0\ \text{kg}$ ball on a shelf $1.5\ \text{m}$ high has $mgh = 2.0\ \text{kg} \times 9.8\ \text{m/s}^2 \times 1.5\ \text{m} = 29\ \text{J}$ of potential energy. Falling to the floor, it reaches the ground with $29\ \text{J}$ of kinetic energy.

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