FACTORS AFFECTING SKI BASE SLIDING FRICTION ON SNOW

The optimum ski base structure roughness varies under different snow conditions according to the generated frictional water film thickness under the ski and the roughness of the snow surface. Thick water films correspond to coarse ski base structures, while it is advantageous to use finer ski base structures and increase the water film thickness when the water film is thin. The friction under a ski is often dominated by solid friction in the front, surface tension in the middle, and viscous drag at the rear. This indicates that the ski base structure ought to be different in the length direction of the ski. Thus, a fine structure that effectively induces and increases the water film production should be used at the front part of the forebody of the ski, at least for cold snow and snow with negligible free water content. As the development of water film possibly increases along the ski, structure with regularly higher roughness should be applied. The dry friction process is dominated and characterized electrically by accumulation of electrostatic charges in the ski base contact points. The frictional water film initiates discharge of potential differences between ski and snow because of the much higher electrical conductivity of water relative to snow. When the air gap volumes between the water film and the ski base structure, and the water film and the snow surface get small, the electrostatic pressures in the air gaps increase, and suction or drag may start occurring. The ski base structure topography and the snow surface topography is decisive for the electrical contact configuration between ski and snow.