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Friction
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Friction is obviously an important factor of cross country skiing. On one hand, friction is necessary because without it a skier wouldn't be able to ski up hill or even move on flat surfaces. However, when racing, skiers prefer to have the smallest friction force working on them possible. In order to reduce the frictional forces which would slow them down, skiers wax the bottom of their skis. The types of wax which they apply to their skis have different functions. The hot wax which is applied to the entire ski reduces the friction between the ski and the snow. This allows the ski to glide on the snow and gives the skier more distance for each stride. Another type of wax is applied to the "kicker". The kicker is the area under the bindings. In other words the kicker is the area where most of the gravitational force of the skier is applied. Skiers apply a type of wax to the kicker that will cause the friction coefficient to increase. This allows skiers to be able to push off and ski uphill. In order to begin their outdoor adventure,
a skier must first face the forces of static friction. Static friction
is the force that keeps the skier at rest. As the skier overcomes
the static friction there is a point where the coefficient of friction is
greater than that of the kinetic friction that resists the skiers motion.
It is clear to see this concept in the figure below.
From the figure above, it is also easy to see that the kinetic friction remains almost constant for a range of speeds. This kinetic friction is the force which slows the skiers down after they start moving. |