Ice skating, how does it really work?
Yup, this is true that the pressure is too small, but the true explanation is not justified yet. Nevertheless the common sense is that there is a lubricating film of water or at least anomalous ice. For an overview, see: http://lptms.u-psud.fr/membres/trizac/Ens/L3FIP/Ice.pdf
The assertion that the skate does not exert enough pressure to melt ice is wrong. Imagine that the skate is lowered vertically until it touches a perfectly flat surface of ice. The initial contact area (before the blade starts to sink into the ice) would be incalculably small and the initial pressure incalculably large because of curvatures. A typical freestyle blade’s “rocker” has a radius of 6 feet; its “hollow” of 7/16 to 10/16 inch. The blade is typically 0.15 inch thick, so its two edges have “bite” angles of 7 to 10 degrees. The rate at which an edge could melt ice and sink in would be limited by heat conduction. In a dynamic situation, with the skater gliding along at a good speed, viscous dissipation in the thin layer of lubricating water would generate some of the heat. If the skater’s trajectory is curved but the rocker’s curvature multiplied by sin(tilt) is poorly matched to the curvature of the trajectory, then there will be additional friction and sound effects as the edge chews up the ice.
This question has been hotly contested for ages.
Calderon & Mohazzabi $ ^{[1]} $ give an excellent summation of the various theories proposed through the years to explain why ice is so slippery in their paper "Premelting, Pressure Melting, and Regelation of ice revisited"
They offer both theoretical and experimental evidence that neither pressure melting nor friction melting alone explain the phenomenon and conclude from atomic force microscopy, among other evidence, that there is a pre-melting Quasi-Liquid surface layer with special properties - This was originally proposed by Faraday and Thompson back in the 1850s - that, in conjuxtion with some pressure melting, make ice skating possible.
Actually they point to other research that shows ice is not the only solid behaving differently on the surface when near its melting point. The main reasons we notice ice is because it is one of the few substances we encounter that is near its melting point when we do encounter it and its abundance.
Ski-ing is also helped along by friction melting once movement starts.The weighted wire cutting through the ice, however, is pressure melting and regelation.
Another paper that summarises previous research well is that by Dash et. al. $ ^{[2]} $
Both papers referenced also give a good set of references for further reading.
References
- Calderon, C. and Mohazzabi, P. (2018) "Premelting, Pressure Melting, and Regelation of Ice Revisited." Journal of Applied Mathematics and Physics, 6, 2181-2191. https://doi.org/10.4236/jamp.2018.611183
Preview/read online at : https://www.researchgate.net/publication/328766489_Premelting_Pressure_Melting_and_Regelation_of_Ice_Revisited
- Drake, J.G., Fu, H. and Wettlaufer, J.S. (1995) "The Premelting of Ice and Its Environmental Consequences." Reports on Progress in Physics,58, 115. es. Reports on Progress in Physics,58, 115. https://doi.org/10.1088/0034-4885/58/1/003