The law of conservation of energy shows that, when only conservative forces act on an object, the object’s total mechanical energy—the sum of its kinetic and potential energy—is unchanged. Conservation of energy provides a “shortcut” to understanding motion, allowing us to predict aspects of complicated motion without getting into intractable mathematical details. Sometimes we’re concerned not so much with energy as with the rate at which we do work, consume energy, or transform energy from one kind to another—power describes this rate.