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Re: misconception re ice melting under skates



I'm afraid I've been guilty of passing this on! Would someone tell me
what is_ happening under the skates or under the loaded wire cutting
through ice? Crawford

Leigh Palmer <palmer@sfu.ca> writes:

Whoa! Those are two very different phenomena. One does not skate on
ice at melting temperature.


Leigh... Please explain. I have skated on ice at melting temperature many
times.
I have not tried to skate on ice when it is very cold.... but I have been
told
that it is difficult to do so because there is too much friction between
the skate
blades and the ice.

Sorry, Herb; that was a silly statement. *Usually* one does not skate
on melting ice, mostly because it is not fun to fall and soak one's
clothing. When ice is at -15 F it is indeed sticky, but one can skate
on it over a wide range of below freezing temperatures. The surface
of ice on a lake in steady state will likely be between the melting
point (which is the temperature at the bottom of the ice sheet) and
the air temperature (which is the temperature at the top of the ice
sheet). If the air is below 32 F and you are skating (meaning the ice
is thick enough) then the surface of ice is likely also below 32 F.

Also, after someone has skated on ice, it is apparent that melting and
regelation have occurred because a smooth track appears along the
path where the blades have passed.

Refreezing does occur if there is appreciable water on the surface.
The term "regelation" has come to subsume the phenomenon of melting
under compression, however, and skating on subfreezing ice won't
produce melting under compression. According to that clip from NPR to
which we were directed last week, there is a very thin film of liquid
water on the surface of ice for some appreciable range of
temperatures below the melting point. It is my impression that the
phenomenon of lubrication of the blade is not well understood, but
calculation does not support the phenomenon of pressure melting
(improperly called "regelation") as the underlying mechanism; that
is well understood.

Herb Gottlieb from New York City
(Where it is too warm this winter to skate on any of our ponds or lakes)

Leigh, from Deer Lake in Burnaby British Columbia, where we had only
one day of skating on our lake this year, and it was not firm enough
to skate all over the lake. Outdoor ice skating on a fair sized lake
with glassy smooth ice is a most glorious outdoor experience.