Re: misconception re ice melting under skates

[Igal Galili <igal@vms.huji.ac.il>]

Leigh,
In response too your comments:

> I am unwilling to believe that there is appreciable heat flow
> *along* the wire. If the ice cube is melting then icewater is
> running down the wire anyway.
>
> A calculation of this phenomenon reveals that the thermal
> conductivity of the wire is important, but only because heat
> is conducted *across* the wire from top to bottom.

> A nylon thread
> should also go through the cube, but much more slowly. Does
> Hewitt claim that heat is conducted in from the room or
> across the wire?

	You are right. Leigh, in your major claim.  I believe that I did
not say anything about the heat transfer ALONG the wire.  This was not the
claim of Hewitt either (thanks, Herb, for your note).  Talking  about the
environment influence I meant the temperature of the ice itself.  I just
responded to Ludwik's experiment and its interpretation.  The zero effect
in his outdoor experiment did not demonstrate that pressure is irrelevant
but that the pressure was not sufficient.   "Pressure-phase transition
temperature" relation serves central phenomenology here.  At the same time,
heat transfer ACROSS the wire is an essential component in the rigorous
account for the real experiment (William Beaty's suggestion of an
experiment with a compound copper-nylon thread would a spectacular
demonstration of this point).
	Finally, I apologize for possible distortion of Hewitt's conceptual
presentation of regelation phenomenon which I think was correct (including
the across heat transfer).  His remark that [plastic] string would not do
it could be understood within reasonable approach.   Of course, nylon
thread will do it [if a copper wire did!], but slowly.  How slowly? -  In
correspondence to its heat conductivity, which is not zero.  In a
conceptually oriented course, it is legal to idealize  illustrations and, I
think, it is OK.
	For me this discussion illustrates the everlasting contradiction
between the demands of phenomenological and rigorous presentations of
physics.  Both extremes are simply not feasible.  Each physics teacher
prepares  a unique ratio of mixture of both approaches in each particular
circumstances.  A beautiful play.
Igal.