Investigating dry ski–snow friction

The easy gliding of skis on snow has long been attributed to several co-existing mechanisms, including dry friction, lubrication by frictional meltwater, and capillary suction, making it challenging to isolate their individual contributions. Experimental evidence that characterises ski–snow friction mechanisms remains scarce. In this study, we focus specifically on dry friction. Experiments were performed on a linear tribometer using a flat slider at –8 °C under conditions where previously no frictional meltwater was observed. The temperature was further reduced below –30 °C using dry ice to eliminate the potential influence of the quasi-liquid layer, thereby ensuring that dry friction was the only active mechanism. Additionally, frictional behaviour under conditions representative of cross-country skiing was investigated. The friction coefficient decreased with increasing speed at a temperature below –30 °C, but increased with speed at –8 °C. Increasing pressure reduced the friction coefficient at both temperatures. A comparison of the measured friction coefficients with theoretical considerations indicates that the primary friction mechanism is the tearing out of grains below –30 °C, and the shearing off the tips (abrasion) at –8 °C. Overall, the results demonstrate that friction under all the investigated conditions can be explained by the stated mechanisms, along with mechanical and thermal effects and granular lubrication, without invoking any influence from the quasi-liquid layer. While it is difficult to explain friction on ice without the help of the QLL, its role in friction on snow appears to be far less significant.