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Control during alpine skiing is achieved principally through the mechanical interaction between the ski and the snow. In that the nature of this interaction is basically a cutting or machining process, it is proposed that the complex physical and mechanical properties of the snow responsible for its skiability can be related to its machinability. A simple testing device is presented, which can machine the snow while keeping the ratio of the thrust (vertical) to cutting (horizontal) forces equal to the tangent of the edge angle. The edge angle is varied to find a critical angle such that skidding occurs at large angles and holding at smaller angles. Using traditional machining theory, it is shown that this critical angle should be a function of the shear-strength-to-hardness ratio of the snow. A plot of critical angles versus shear-strength-to-hardness ratios is presented, which divides the surface into carving or holding and skidding regions.
Critical angles have been measured between about 40 and 70°. These angles correspond to shear-strength-to-hardness ratios between 0.24 and 3.84. The difficulty of relating this critical angle to some function of maximum skiable slope steepness is discussed relative to ski technique and forces on the ski.
snow, skiing mechanics, snow mechanics, ski areas, sports equipment, ski design, skiing safety, snow properties, machining, cutting
Scientific collaboratorassistant professor, Swiss Federal Institute of TechnologyWorcester Polytechnic Institute, LausanneWorcester, MA
Professor of mechanical engineering, The University of Vermont, Burlington, VT