Why do waves break on the shore?
Consider the following picture (1). As the wave moves in to shore, the bottom gets shallower and shallower. Now, it turns out, for waves in water, if the bottom is shallower, the wave moves slower. As the wave approaches the shore, the leading edge of the wave is in shallower water than the trailing edge (2). (1) (2) The top of the wave tumbles forward, eventually breaking over the leading edge. (3) In this one limited situation, it is true that for a short time the water is actually moving forward with the wave; the water in the crest of the wave is carried forward by its greater speed.
