The kinetic energy of a moving object is directly proportional to the object’s weight. A vehicle that is twice as heavy has twice the kinetic energy. The kinetic energy of a moving object increases as the square of the object’s speed. Doubling the speed quadruples the kinetic energy (i.e., multiplies it by four). Brakes use friction to convert the kinetic energy of a moving vehicle into heat. Thus, if you double a vehicle’s weight and double its speed, it will take 2 × 4 = 8 times as much braking power to stop the vehicle.