The Physics of Surfing (Part One: Dropping In)

[P]addling by itself doesn’t get you into the wave, because you actually cannot paddle as fast as the wave is moving, and you need to match the speed of the wave if you want to ride with it. In order to catch up to that wave speed, it’s necessary to use the gravitational potential energy of the wave. The trick is to obtain sufficient speed by paddling that, as the wave travels under you, your board begins to fall down the face. As you drop down the front of the wave, the gravitational potential energy you gain is converted into kinetic energy. Soon you are travelling as fast as the wave. In fact, if you continue to drop to the bottom of the wave, you’ll be moving faster than the wave — and if you don’t cut into the face, you might temporarily outrun it.