When you think of the beach, you probably also think of waves. These are almost always found on the coast. But why is it that those waves always come straight towards the coast, and not in an angle?
Water in motion
Waves are generated by the wind blowing over water. Waves move the water to a few meters deep. In deep water, the waves can continue to wave gently. But as soon as the waves get into shallow water, the bottom changes the direction of these waves. Near the coast, the water is shallow. The waves have to deal with the bottom there. Friction is created. The friction slows down the wave.
The shallower it gets, the stronger the wave slows down. For example, if a wave arrives diagonally on the coast, the
part closest to the coast is strongly slowed down. The front part of the wave slows down, but the rest waves a bit faster, so that the rear part of the wave can catch up. That way the direction of the wave changes. This is called wave refraction. Ultimately, all parts of a wave are the same distance from the coast. And the wave comes perpendicular to the beach.