In a wave, what occurs at the crest?

At the crest of a wave, maximum displacement of the particles occurs in the upward direction. This means that at this point, the energy is at its highest, and the particles in the medium through which the wave is traveling are displaced the furthest from their equilibrium position in an upward direction.

In a transverse wave, such as water waves or waves on a string, the crest represents the peak point of the wave’s oscillation above the rest position. When particles reach the crest, they have moved as high as they will during that cycle, demonstrating the wave's energy is maximized at that point. The movement of particles transforms energy as the wave propagates, which is illustrated by the upward displacement at the crest.