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When we throw a stone in a quiet pond, circular ripples concentric about the point of disturbance emerge on the surface of water that moves outward from that point of disturbance. These ripples are the waves or more precisely surface waves. Though the spreading pattern of these surface waves seems nice and simple, the physics behind it is quite complex/ First, the stone displaces the water molecules at the point of impact from their equilibrium positions. These molecules through the surface to vibrate about their mean position. So, a kind of disturbance seems to propagate radially outward from the point of impact. This disturbance traveling from one point to another point is called a wave in motion. During wave motion, the particles though displaced from their mean position, do not actually travel from one point to another. Rather, they transfer their energies to neighboring molecules during the vibration and it is the energy that is being transported from one point to another. Thus we can say that wave motion is a mode of energy transfer from one point to another point.
As an analogy, the following example is relevant to understand wave motion. When a person standing at the last of a very long queue pushes another person in front of him, he loses his balance and all other people ahead in the queue receive a gentle push and hence lose balance to some extent. However, all of them in the line manage to return back to their initial position. Therefore, the disturbance in the form of a push created at the end of a queue traveled throughout the queue to the front. But, there is no actual displacement of the person in the queue from end to front. This is the real way of wave motion in a material medium. On contrary, a running stream of water carries energy with itself as it moves along. This way of energy transfer is not of interest in the present situation.
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