What type of friction is surfing

Surf wax friction tests seems especially difficult to measure. Before I show you my test apparatus, we need to do some physics to figure out how to solve for the coefficient of friction. A surfing friend of mine once commented something to the effect that geometry was fairly useless. Here is a case where it is not useless. The method to determine the coefficient of friction is basically a geometric proof. The idea is to use some physics to draw a free body diagram, manipulate some force vectors and derive an equation that quantify the effect of friction.

Figure 2 shows the free body diagram, various geometry relationships and the force vectors. One can find this derivation in most college freshman physics texts and some high school sources. The punch line is: The tangent of the angle of inclination is the coefficient of friction. The trick to this exercise is knowing that the angles shown in the figure are the same which is a geometric proof for similar triangles.

This would be something done in high school geometry, though it is a bit confusing and I commonly forget the proof. Now I have just memorized that it works. Anyhow, some geometry allows us to do a simple test and calculate the coefficient of friction by raising an inclined plane and watching something slip down. So how do I use that information. Now we get to the test set-up.

See figure 3 for my test set-up. In this figure I have a surfboard which has been waxed. I actually waxed it with different waxes in different locations so I can test various waxes together for comparison. I have attached a shop crane to the tail of the board, so I can slowly raise the board at an angle from horizontal. You can see the result of the collision by watching the spray of water squirting out around the edges of the surfboard.

The hydrodynamic forces also include drag forces as water slides along the bottom of the surfboard. The hydrodynamic forces are potentially quite large, as any surfer who has fallen under a breaking wave can attest. Very subtle shaping of the bottom of the surfboard can strongly affect the performance of the board. Channels, concavities, and curves imposed on the bottom of a surfboard that can hardly be seen or felt without comparing them to a straightedge can change the hydrodynamic forces on the board substantially.

As you ride a wave, you savor the rush of acceleration as tons of moving water pushes you faster and faster. You stand up on the board with your knees bent, hanging loose. You balance side-to-side and front-to-back, keeping the continuously changing forces and torques in balance. In a sense, you are dancing with the hydrodynamic forces.

The Wave Breaks As the wave moves into shallower water, it begins to interact more with the sandy bottom of the sea. The curious story of Mr. Zog's Sex Wax. Share this article. Share on Facebook. Share on Twitter. Looking at surfing principles and the forces in surfing, we need speed and power to surf critically and to surf at a high level. Speed, power and flow are one of the major elements in the Judging Criteria for surfing competitions and thus are a vital component of performance surfing.

Even for recreational surfers, the more speed, power and flow a surfer has, the better they will be surfing! When we catch a wave, we have a number of both external as well as internal forces acting upon us while we ride the wave. As the surf board is connected to the surfer, the buoyancy of the board is another force acting that can be considered an internal force.

Some of these forces we can have an affect on, others we cannot. We will very briefly look at the different forces in surfing that are experienced while surfing and what can be done to affect these if a surfer can. Wave Power — This is dependent upon a number of factors and changes continuously. It helps a surfer increase speed as the surfer goes down a wave but negatively affect that surfer when going back up the wave.