Energy

Energy exists in different stores: kinetic, gravitational potential, chemical, elastic, nuclear, thermal, electrostatic and magnetic.

The principle of conservation of energy states that energy cannot be created or destroyed, only transferred from one store to another.

In any transfer:

$\text{total input} = \text{useful output} + \text{wasted energy}$

Wasted energy is usually dissipated to the thermal energy store of the surroundings.