Re: misconception re ice melting under skates

[brian whatcott <inet@intellisys.net>]

At 12:47 2/26/98 -0800, you wrote:
> > ...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.
>
> I believe you have just stated clearly the correct situation, without
> resorting to misconception, in words only, and with little obfuscating
> mathematics. Saying that plastic string won't do it is a misconception
> of the simplest kind. It is not a simplification; it is (simply) wrong.
> Would it have exceded the bounds of reading level to say that the
> plastic string would pass through the cube much more slowly because it
> has a much lower capability for transferring heat than the metal wire?
> (Sorry, Ludwik; that's the way I would do it in a course for
> unsophisticated students.)Leave out the "In correspondence to its heat
> conductivity", but why lie? Hewitt obviously knows the truth and he
> *oversimplifies*. I think that is clearly unjustifiable in this case,
> and I can't imagine any reasonable defense of Hewitt's (reported)
> statement. It can only be defended as a matter of taste, and it tastes
> awful to me!
> ...
> Leigh
It is quite conceivable that Galil and Palmer are right as to the 
possibility of some plastic line traversing an ice block, albeit slowly.

However, despite the high didactic, even inflexible tone conveyed in 
this note, I do not discard the idea that the person who published the 
research paper, Hewitt, may have it right - that a particular plastic 
line may be DEAD-stopped by an iceblock that will permit a metal wire 
to penetrate.
  You see, it seems Hewitt's critics have over-simplified the physics - 
as teachers sometimes do.
 In my view - a controlling parameter is the ratio of thermal 
conductivity in the line to that of the surrounding ice.
If THIS ratio becomes sufficiently low ( for a particular diameter 
of lines) then the latent heat is dissipated in side ice where it 
does not contribute to the desired effect, rather than ice in the desired
plane where it is needed.

Whatcott