Energy is not only continually changing form - it is also continually moving from one place to another. One way this occurs is through wave motion. When a stone is dropped into a pond, at first only the moving stone has energy. But after a while, a leaf on the far side of the pond will bob up and down as the ripples reach it. Now the leaf has energy, too. The ripples have transported some of the stone's energy across the pond. Water waves or ripples are just one kind of wave. They are called transverse waves because, while the waves move outward from their source, the individual water particles move up and down only at right angles to the waves direction. Another kind of wave is called the longitudinal wave. In these waves the particles move back and forth in the same direction as the wave. Sound waves are of this type.