Imagine you are working against gravity by lifting a heavy object—for example, a brick. It takes energy to lift farther brick, and conservation of energy says that energy is never lost. Where does that energy go? It is changed into a form called gravitational potential energy. The energy is stored in a way that resembles how energy is stored in a battery. Potential energy is energy that has potential—it is waiting to show up in a more obvious form. If you drop the brick it falls, and as it falls it speeds up. The gravitational potential energy that was stored is converted to energy of motion, which, as you may recall from Chapter 5, is called kinetic energy. When the brick hits the floor, it stops suddenly. The brick loses its energy of motion, so what form does this energy take now?