A ripple tank is a tray of water into which vibrations are introduced using a frequency generator. In the ripple tank shown here, a rod is used to generate waves that travel in parallel across the tank from back to front. In other cases single points can generate concentric circular waves or pairs of points can generate pairs of waves emanating from two different points.

A mechanical wave is a moving disturbance in a material, such as the water in this ripple tank. As a wave passes, the particles of the material oscillate about their original positions, but there is no net displacement. What does move with a wave is energy.