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Saturday, January 21, 2012

Wax

To cross country ski is to live a paradox. The skier must glide frictionless on the snow but has to stick to the snow in order to propel forward. To do this the skier has to rely on one thing- wax. A classic ski has two types of wax, glide and kick.  Glide wax is applied to the length of the ski and provides a nearly frictionless surface that allows the ski to slide across the snow. Kick wax is applied to the “kick zone”.
The kick zone is below the foot and somewhat variable but generally extends several inches in front of the toe and just behind the heel. Kick wax is a bit more interesting than glide wax because, like the kick zone, it is variable.  Different kick wax is used based on the temperature. The general idea behind kick wax is that it lets the ski stick to the snow. However the way it works is a bit different. The wax actually allows the snow to stick to the wax. 
Snow has a crystal structure that makes it rather rough at the microscopic level.  The rough snow surface grabs onto the corresponding rough surface of the wax and allows the skier to push, or kick forward. If the wax actually stuck to the snow it would be disastrous for the skier because snow would build up on the bottom of the kick zone and reduce the ability to glide. This actually happens when the wax applied to the ski isn’t matched to the size of the snow crystals on the trail.  
Fortunately skiers don’t have to carry specialized equipment to the trail in order to gauge the microscopic magnitude of the ice. All they need is a thermometer.  How does a thermometer predict the size of snow? The answer is the same answer that makes all of science work.  The natural world is predictable.
Snow crystal size is dependent on temperature just like the descent of an apple to Earth as it falls from a tree is predicted by the force of gravity. Science has exposed countless predictable phenomena and relies on this predictability to explain new observations, make predictions about yet unobserved events and even helps skiers stick and glide on snow.

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