The following experiment shows that in wave motion, only energy is transferred, but particles of medium do not leave their positions.
Experiment —
If we drop a piece of stone in the still water of a pond, we hear the sound of stone striking the water surface. A disturbance is produced in water at the point where the stone strikes it. This disturbance spreads in all directions radially outward in form of circular waves on the surface of water as shown in the figure below.
Now, if we place a piece of cork on the water surface at some distance away from the point where the stone strikes the water, we notice that the cork does not move ahead, it moves up and down while the wave moves ahead.
The reason is that the cork along with the particles of water (or medium) start vibrating up and down at the point where the stone strikes. These particles then transfer their energy to the other neighbouring particles and they themselves come back to their mean positions. This process continues and thus the disturbance moves ahead on the water surface in form of wave.
Therefore, the above experiment shows that particles do not move but only transfer energy to other particles.
