How about this: When you throw a ball, you are converting the potential energy in your body to a kinetic energy stored in the ball. In order for the ball to sl

How about this: When you throw a ball, you are converting the potential energy in your body to a kinetic energy stored in the ball. In order for the ball to slow down, something has to get that energy out of it. Since energy can't be destroyed, the ball is forced to keep going forever until the kinetic energy is taken away.