If the speed of a moving object is cut in half, its kinetic energy is reduced by four times. Kinetic energy is defined as the amount of energy an object has because of its motion.
Kinetic energy is measured in joules. The equation used to determine the amount of kinetic energy an object holds involves both the weight of the object and the speed at which the object is moving. Kinetic energy, or the number of joules, equals the weight of the object multiplied by the square of the object's speed. If the speed of the object is cut in half, the kinetic energy is reduced at a rate of two squared, or four.