661. What causes a dropped ball to bounce? - MK
When you lift a ball off the floor, you transfer energy to it. This energy is stored in the gravitational force between the ball and the earth and is called gravitational potential energy. When you release the ball, its weight makes it accelerate downward and its gravitational potential energy gradually becomes kinetic energy, the energy of motion. When the ball hits the floor, both the ball's bottom surface and the floor's upper surface begin to distort and the ball's kinetic energy becomes elastic potential energy in these two distorted surfaces. The ball accelerates upward during this process and eventually comes to a complete stop. When it does, most of the energy that was initially gravitational potential energy and later kinetic energy has become elastic potential energy in the surfaces. However, some of the original energy has been converted into thermal energy by internal frictional forces in the ball and floor. The distorted ball and floor then push apart and the ball rebounds into the air. Some or most of the elastic potential energy becomes kinetic energy in the ball, and the rising ball then converts this kinetic energy into gravitational potential energy. But the ball doesn't reach its original height because some of its original gravitational potential energy has been converted into thermal energy during the bounce.