Waves behave differently depending on whether they're in the open sea or near the shore.

Out in deep water, the wave shape moves, but each particle of water returns nearly to its starting position once the wave passes. To see how this works, imagine a giant cork floating in the deep ocean. As a wave goes by, the cork bobs up and down and sways from side to side, but actually doesn't move much from where it started. The wind does drag the water a bit, and that's what creates ocean currents such as the Gulf Stream.

The behavior of a wave changes as it approaches the shore. Once in shallower water, the wave feels the bottom. It slows down, its height increases, and its front steepens. Eventually, the wave collapses, or "breaks," creating the turbulent water we call surf. Almost all the energy that originally went into creating the waves is dissipated in the surf. That energy powers erosion and sets sand and sediment in motion.