How Waterskiing Works

Physics of Waterskiing


In order to understand how waterskiing works, it's helpful to know the principles of physics underlying the sport. In order to waterski, several factors come into play.

First of all, you should acquaint yourself with the basic characteristics of water. Fluids in motion can be characterized as turbulent and laminar. While turbulent water in motion has a rough surface and irregularities in its flow, laminar water is smoother. The formula, called the Reynolds number, used to compare the two types of water is:

Re = P (density) x L (obstacle length) x V (flow speed) / v (viscosity or internal friction)

A higher Reynolds number indicates a more turbulent fluid. A lower number suggests laminar water, which is optimal for water skiing because it's smoother and maintains a certain flow.

Before you take off, make sure the tips of your skis are kept out of the water. By lifting the tips of the skis out of the water, your position will apply pressure that will counter the force of the boat when it begins to pull you. The tilt of the ski is the source of the lift that will pull you out of the water. With the ski tip tilted up, the water will strike your ski as you move forward, creating a rebound downward from the ski. This will create an upward force on the ski and you. As long as the force of the upward water is equal to the downward force of gravity, and accordingly the weight of the skier, you'll stay afloat. Gravity is a constant force that determines the weight of the skier, skis and the air above the water. Water counterbalances the weight above its surface.

Newton's Third Law of Motion states that for every action there is an equal and opposite reaction. When the boat accelerates, it'll begin to pull you. Accordingly, you will supply the equal and opposite pull against the boat. That is, you'll lean back to counter the force of the boat. Since the force of the boat is much greater than your own, it will pull you up and out of the water.

There's more to learn about the laws of motion on the next page.