Abstract
The friction of a stationary moving skate on smooth ice is investigated, in particular in relation to the formation of a thin layer of water between skate and ice. It is found that the combination of ploughing and melting gives a friction force that is rather insensitive for parameters such as velocity and temperature. The weak dependence originates from the pressure adjustment inside the water layer. For instance, higher velocities, giving rise to higher friction, also lead to larger pressures, which, in turn, decrease the contact zone and so lower the friction. By treating ice as a Bingham solid the theory combines and completes two existing but conflicting theories on the formation of the water layer.
Highlights
Ice seems to be the only substance on which one can conveniently skate, which prompts the question: “what sort of special properties does ice have as compared to other solids?” one can glide on ice over a wide range of velocities, types of skates and temperatures
14 Discussion A Velocity and pressure in the water layer B The y dependence of the water layer C The slow velocity limit D Heat transfer in the water layer E Heat flows in the ice References
Skating is a minor beneficiary of this property, as canals freeze on top, so one does not have to wait till the canal is solidly frozen. Another interesting property of water is that the melting line in the pressure-temperature plane has an unusual slope: with increasing pressure the freezing temperature lowers, while usually pressure favours the solid phase. It is illustrated in the famous high-school experiment where a steel cable with weights on both sides, melts itself through a block of ice at temperatures below zero, such that the block refreezes on top of the steel cable! This property has featured for quite a while as explanation for skating: due to the pressure exerted by the skater on the ice, a water layer forms and the skates glide on this water layer
Summary
Ice seems to be the only substance on which one can conveniently skate, which prompts the question: “what sort of special properties does ice have as compared to other solids?” one can glide on ice over a wide range of velocities, types of skates and temperatures. This property has featured for quite a while as explanation for skating: due to the pressure exerted by the skater on the ice, a water layer forms and the skates glide on this water layer. In this paper we study the formation and influence of the water layer underneath the skate for usual conditions, i.e for sliding velocities of meters per second and temperatures of a few degrees below the melting point of ice. Gliding is only a part of the physics of skating. The only measurements of the friction of skates under realistic conditions, that we are aware of, have been performed by de Koning et al [2] Their skater had a velocity of speed of V = 8 m/s and a weight of 72 kg. In addition a number of separate issues are treated in Appendices
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