Why is ice slippery if pressure doesn't lower its melting point?

[yileili3]

An often encountered but incorrect answer would be that the pressure on the ice lowers its melting point. This doesn't make much sense since this effect can only lower the melting point of ice by a very small amount 1C by a simple calculation in thermal dynamics.

So the question is, what makes ice slippery so that people can skate?

 

[HallsofIvy]

Why does that not make sense? Typically, the surface of ice will be close to 32 degrees Fahrenheit so that slight increase in temperature will melt a tiny bit of the surface and so make it slippery.

(If you really freeze ice so that even it surface is well below freezing, you cannot "skate" on it- pressure will not make it slippery.)

 

[yileili3]

Well, you do see people skate when it is much colder than 32 degrees Fahrenheit, which the simple answer cannot explain.

 

[Curl]

OP is correct, the melting point is reduced by less than 1 degree, and the ice temperature is perhaps -5 or -10C or so. It is a myth that the ice melts under the skate.

I think the reason is because ice has a very low coefficient of friction... as to why, it has to do with friction theory, and this I don't know. Maybe someone else has an answer.

 

[ZapperZ]

Read this:

http://lptms.u-psud.fr/membres/trizac/Ens/L3FIP/Ice.pdf

There are other papers on why ice is slippery and why we can skate on ice. The pressure-melting reason is not quite accurate.

S. C. Colbeck et al., Am. J. Phys. v.65, p.488 (1997).
S. C. Colbeck, Am. J. Phys. v.63, p.888.

Zz.