INTRODUCTION: The kinetic frictional coefficient (micro k) of skis shows a very small value and typically is explained by the meltwater lubrication theory (Bowden and Hughes). Colbeck and Warren provided experimental evidence for frictional heating by fastening a thermocouple to the bottoms of downhill and skating skis. However, even with the contributions of theory and evidence, the best thickness of the water film for sliding skis on snow and the real contact area is still unknown. We observed the micro k of short sliders at lower than -10 °C. The values at low speed and low temperature, in other words, no melt-water, show comparable values with those of Alpine skis at high speed and the best skiing temperature (-3 to -5 °C). METHOD: Two different observations were performed. 1. The natural slide method: A model ski (10 to 30 cm length) slides on a flat snow packed slope. The slider position is observed by means of an ultrasonic distance sensor (sampling time; 17.5 ms, accuracy of distance at 0.5 m/s; 8 mm). The sliding speed, the acceleration and then the micro k are deduced by the distance data and the time. 2. The rotate snow-truck method: A model ski is strapped to a static frame via a load cell and a large snow-table (diameter; 1.8 m) is rotating under the ski. m of last item in the list. Fig.1 indicates that the lower the snow temperature, the smaller the micro k values for any snow and different length of slider. The average sliding speeds were less than 0.5 m/s. In Fig. 2, the micro k v.s. sliding speed shows the maximum value at only the low snow temperature. DISCUSSION: The existence of liquid-like layer which covers the surface of ice was observed recently with many ways such as the proton backscattering or the atomic-force microscopy. Temperature dependence of the micro k at slow speeds seems to be explained by the resistance based on the adhesion with the liquid-like layer.
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