Physics of Ski Waxing

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Skiing is one of the things to do during the winter, here in Canada. It is also cheap and easy to start, since there are ski-tracks almost everywhere and it is possible to find used skis for less then $50. Skis are pretty simple in design. Originally they were designed just as the snow shoes, though today they are much more advanced. (Wikipedia) Skis can be used just after you bought them, without doing anything to them. However, if you want your skis to perform to their best, simple maintenance needs to be performed. One of the best and easiest way to do so is to apply wax. One can be confused at first by the variety of waxes available on the market. To see that, just check ski section in local Beaver Sports store. In reality, just one or couple waxes needed to get started. I'm going to explain how to wax your skis for the diagonal stride technique and what exactly waxing does to the skis.

Ski structure

Cross country skis are bent vertically. That allows for using different kind of wax depending whether person is sliding or kicking.

When buying skis, you should choose ones that are made for your mass. If they are for bigger person, skis will be less bendable, thus area of contact will be only on the ends. If they are for smaller person, skis will be unbent most of the time. That is not very good, because it would slow the person down. Ideally we want all the area of the ski to be in contact with the snow when pressure is applied and middle section off the snow when sliding.

Friction is force dependant, meaning it changes depending on force applied.

Ff = F * μ

Glide wax is applied to the front and the end of the skies, this way when person removes force from one leg, friction becomes less and ski slides.

The ski is unbent when force is applied to it. Friction between snow and wax in the midsection increases so that it grips enough for a kick. Coefficient of static friction of the kick wax is only big enough for "the snow irregularities dig into wax irregularities just enough to give a motionless ski bite, or grip." (Brady)

At the moment when ski gains velocity, it is not at rest anymore, and since μk is less then μs, friction is not big enough to hold the ski.

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