Nicole Jones
Physics 1090
10-26-09
Labor 2

Chapter 2, Question 69: Surfing

I have lived my entire life in Wyoming, but I have always wanted the opportunity to learn how to surf. I am fairly certain that I would be absolutely horrible at surfing because I have very little coordination, especially when it comes to sports. But I have always wanted to surf which is why the question from The Flying Circus of Physics about surfing caught my interest. What causes a surfer (on a surfboard) to move toward the beach or along a wave? Can you surf the top of the wave or on the backside?

First of all, a surfer can only ride a wave if the top of the wave outruns the bottom and the wave spills or plunges. If the wave simply surges or collapses, the water simply rushes forward and the wave is useless for surfing. A wave is also useless for surfing if turbulence appears along the whole wave at the same time. These kinds of waves are called closeouts (Surfline). If the turbulence begins at one end of the wave and the wave peels, the surfer can ride the wave just ahead of the turbulence.

There are three basic forces acting on a surfer as he rides a wave. Buoyancy keeps the surfboard floating, gravity pulls the surfer down the face of the wave, and the frictional drag of the surfboard in the water pulls against the gravity and the slope of the wave. Drag opposes the motion of the board through the water because of water pressure in front of the board and the friction between the board and the water. The surfer can ride the wave and change position by shifting his weight and thus changing the drag of the surfboard. To begin, the surfer paddles out to breaking waves. When a wave comes up under the back end of the surfboard and lifts it, the surfer pushes up into a crouched position (Bryner). By shifting forward, the surfer can move down the front face of the wave because there is less drag from the back of the board. Oppositely, if the surfer shifts back and forces the back of the board to dig into the water, he creates more drag and the board moves up the face of the wave.

Here is where it gets a little trickier. There are three forces acting on the surfer- buoyancy, gravity and drag. However, these forces do not pull in exactly opposite directions because there are three of them. Gravity pulls straight down, but the buoyancy force pulls parallel to the wave face and the drag pulls perpendicular to the buoyancy force. Essentially, all three forces cancel out and the surfer is in equilibrium until he shifts to change position on the wave.

Annotated Bibliography

Bryner, Jeanna. “Worldly Waves.” Science World 8 May 2006. eLibrary. Sheridan College, Sheridan, WY. 20 October 2009. .
Surfline. 2009. Surfline/Wavetrack, Inc. 20 October 2009. .
Walker, Jearl. The Flying Circus of Physics. 2nd ed. John Wiley and Sons, Inc., 2007.