Energy and work units conversion calculator for metric (SI), U.S. customary and imperial measurement systems.

In SI (International system of units) the derived energy and work unit is joule (J). In U.S. and imperial system, the common energy and work units are pound force foot, British thermal unit (Btu) and horsepower hour.

__Energy and Work__

**What is Energy ?** Energy is a measure of how long we can sustain the output of power, or how much work we can do. There are two kinds of energy: potential and kinetic.

**Potential energy** is the energy waiting to be converted into power. Gasoline in a fuel tank as an example.

**Kinetic energy** is the energy a body possesses because it is in motion. The more the object weighs, and
the faster it is moving, the more kinetic energy it has. The formula for kinetic energy is:

**Kinetic Energy = m * v**^{2} / 2 , where "m" is the mass and "v" is the velocity.

**What is Work ?** Work is the application of a force over a distance. Work is equal to the product of the force and the distance through which it produces movement. Although both force and displacement are vector quantities, having
both magnitude and direction, work is a scalar quantity, having only magnitude.

If the force acts in a direction other than that of the motion of the body, then only that component of the force in the direction of the motion produces
work. If a force acts on a body constrained to remain stationary, no work is done by the force. Even if the body is in motion, the force must have a component in the direction of motion.