A ball sitting on a shelf has potential energy. An identical ball sitting on the floor does not have potential energy. Why does the ball on the shelf have potential energy?
since the ball has a height to it, it may fall to the floor where the other ball is and convert it's potential energy (because of the height) to kinetic energy
Potential energy is the ability to move because a force is acting on the object—the ball on the shelf possesses gravitational potential energy. It is a distance above the zero point (the lowest possible place it can fall to) and thus the force of gravity has the potential to move it. The ball on the floor, on the other hand, cannot fall any farther and thus has no potential energy.