Energy at rest is called "potential energy." It is also called "gravitational potential energy" because it is a result of an item's mass, position and acceleration of gravity. Potential energy is equivalent to weight multiplied by height, where weight is the multiplication sum of mass by acceleration of gravity.
Acceleration of gravity is considered 32.2 feet per second squared at sea level. Based on the principle of energy conservation, potential energy can be converted into kinetic energy when an object starts moving. Energy is never destroyed or created but converted into another form. Both kinetic and potential energies are forms of mechanical energy. Their standard measurement unit is joules.