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When we ski the force of gravity acts down on our bodies and through our legs into the skis and the snow. Any source of friction will slow down our rate of progress and so skiers have learned to overcome these different forces.
Skiers can reduce friction before even putting on their skis. Properly prepared skis, which have had the bases prepared on a ski grinding and polishing machine will be much smoother than skis that are well used and scored. Skis are routinely waxed after grinding to create the smoothest finish possible. Waxing helps to reduce the friction between the ski base and the snow.
Putting your body into a tuck position will reduce wind resistance considerably. Friction and drag can also be reduced by wearing a ski jacket and ski pants that fit well. There is a compromise between clothing that is so tight that it restricts your movements against clothes that are too loose, so they catch the air and slow you down. When skiing friction is created when you ski from side to side. The energy which could have been used to get you down the run faster is instead used in pushing snow out of the way during a turn. So, the most direct route down the run will always have the least friction.
As you ski downhill your skis push against the snow creating kinetic friction, which in turn creates kinetic energy and subsequently thermal energy. This thermal energy is the heat that is released where your skis and snow are in contact. The more friction, the more heat you generate instead of speed, and the slower you go forward.
Conversely, the more pressure that you put on your skis, the more pressure is applied to the snow underneath and the higher the likelihood that the snow will melt. Essentially skis slide because the layer of snow beneath the ski melts from your kinetic energy, which then creates thermal energy and melts a thin layer of snow.
The ski is then able to easily slide over this layer of water, which reduces friction. Afterward, the melted snow is free to refreeze as ice. You will notice on a run your ski is much freer to slide over the snow surface, this is because the energy can be transferred efficiently from your ski to the snow surface creating water to slide on.
However, in powder snow, energy transference from the ski to the loose powder is much less efficient, so less snow melts and the surface is less slippery.
Skis tend to follow the line of least resistance or friction. If you let go of a ski on a run it will tend to keep going in the same direction because that’s where there is the least resistance.
Similarly, if you ski forward with parallel skis, you will notice there is little resistance or friction. However, if you make a wedge turn (or Snow plough) as you are skiing down the same run you will feel the friction or resistance as the inner edges of the skis bite into the snow. So, taking the most direct route down a run always minimizes the friction.
Skiers can also reduce friction by changing their body posture. Squatting down on your haunches or going into a tuck reduces the body’s surface area considerably. Having an effective tuck position makes a very big difference to wind resistance, and consequently, speed. You can test this for yourself when you’re skiing on a flattish run. By just putting your arms and poles behind your back you will notice you speed up because your wind resistance was lowered.
All skis and snowboards will gradually become slightly scored on the base of the ski however careful you are to protect them. Ski rental shops often have the facility to regrind the bases and take them back to a new condition. The process involves firstly regrinding the edges of the ski to ensure they are sharp. The skis or snowboards are then fed through the grinding machine, which has a stone wheel, which removes a very thin layer of the ski surface.
The final part of the grinding is to re-wax the ski. Melted ski wax is poured onto the base of the ski and a hot iron is used to spread the wax in a very thin layer all over the base of the ski. This is allowed to cool and set completely. A steel or polycarbonate ski scraper can then be used to remove the excess wax from the base of the ski before using a brush to buff the surface.
Ski clothing nowadays is often made from strong and durable man-made fibres. When choosing the fit for a ski jacket and ski pants it is best to go slightly larger because often you will be wearing extra layers underneath for warmth. You need to have good freedom of movement to move your arms and legs as you assume different positions during skiing. However, you don’t want such a large fit that your wind resistance is increased too much.
There are numerous ways to reduce ski friction, some involve changes to clothing and equipment, and others involve different behavior and postures on the runs.