I think that during this last "heat flow" debate that I have gained some
additional insight as to just why there _is_ such a debate -- It has always
been a mystery to me why there is a disagreement.
It could have been any of the posts, but I think that it was Bill Beaty's
pendulum post which gave me a flash. When trying to describe the process
that occurs when one end of a brass rod is heated, most think in terms of
water flowing in a pipe or the like.
It escapes me for the minute who it was who gave us the "heat flow"
equations. LaPlace? But we should remember that this theory was advanced
during a time of the then popular caloric and it was developed quite
separately from the First Law.
Bill's pendulum analogy gives an intro student a reasonable picture of this
process -- sort of a continuous bumping and grinding and vibrating of the
molecules down the rod. And alas this is fairly accurate. And quite
reasonably leads to the language of "heat flow" -- even today.
BUT when we deal with the First Law, we have the enormous propensity to use
a similar language. We want to call Q "heat" and we tend to think of Q in
the same terms as the "flow" down the rod.
When I began this "heat" voyage in grammar school I was comfortable with
this picture too. But when my physics teacher in HS introduced the First
Law -- It wasn't with Feynman's blocks (This was long before Feynman), but
it seems that it was something like that, then the first glimmer of
confusion flickered. Things started not to make sense: How could "heat" be
both in U and in Q???
By my third or fourth time through thermo in graduate school -- from a
quaint prof who had no idea of what I was asking -- let alone a coherent
answer -- I was really confused. The quaint prof was using an equally
quaint text: Pippard, who clearly had no idea of the answer either.
I confess it was not until after years of industrial research and more
years of teachng that the Gardnerian ah ha light flashed -- mostly due to
insightful students who saw the same difficulties I did years earlier.
Q does not flow; it is "done" -- just as W, "work", is done. Q is
_external_ to the system NOT inside it. The "thing" inside is called by
most thermo people "internal energy", U.
Now comes the difficulty: We have built up the enormous momentum -- begun
thousands of years ago --of thinking of the process occurring in the rod
(LaPlace?) and the description of the gas in a locomotive cylinder (Carnot,
et al) as having to do with "stuff".
So my current insight -- long time abrewing -- is, if Bill wants to talk
about the process in the rod as "heat flowing" -- because the concept of
something flowing appeals to him -- conceptually not quite accurate but
acceptable to him -- and many others --, THEN he will have to tell me what
language he wants to use in discussing the First Law!