Re: single-system dQ + dW

["John S. Denker" <jsd@MONMOUTH.COM>]

At 10:35 AM 11/3/99 -0500, Bob Sciamanda wrote:
> At this point I would ask John Denker (or anyone who can) if he would
> recommend engineering texts (preferably at the Junior/Senior undergraduate
> level) which teach his interpretation of the first law of thermodynamics.

I'm going to do the scientific thing and report *all* the data, including
the distasteful data.

1) I recognize that my previous references to _The Feynman Lectures on
Physics_ do not answer Bob's question, since Feynman expressly disclaims
covering the engineering aspects.

2) I went down to the local college bookstore to see what they were using
as a thermo text.  I found  Sears & Salinger, _Thermodynamics, Kinetic
Theory, and Statistical Thermodynamics_ 3rd edition.  I observed the
following:

a) Those authors nearly always use the word "heat" as part of the
expression "heat flow" -- almost is if it were a compount word, "heatflow".

b) When they mention heat other than heatflow, it is generally dressed up
in all sorts of caveats, although on page 77 there is an isolated reference
to "heat in the system".

c) In discussion of dissipative processes and the mechanical equivalent of
heat, they say
        it is imprecise to say "work is converted to heat"
(but alas they don't explain what the problem is).

d) They go on to say that the dissipative process did "dissipative work".
They don't call it heating.

e) They say that dissipation has the same effect "as if" there had been a
heatflow.

================

Having reported the data, now let me comment on it.

I find the idea that there is no "heat" outside of "heatflow" distasteful.
I have tried but failed to find any physical or pedagogical rationale for
this way of looking at things.  Sadi Carnot gave a definition of heat as a
noun, flowing or not, and I just don't see what harm there is in it.

Conversely, I can exhibit reasons why focussing on flow is unphysical and
unhelpful.  The main reason is that whenever there is a discussion of the
flow of XXX, and if all XXX can do is flow from place to place, then
students can logically and reasonably conclude that XXX must be conserved.
Alas thermal energy is not conserved.

Until this morning I thought this fixation on flow was bizarre and
unconventional.  But (pending further research in bibliopathology) I may
have to back down.  I still think it is bizarre, but maybe not totally
unconventional.  Sears had been co-authoring thermo books since before I
was born, and he has more standing than I do to say what is conventional.

==============

Moving forward:  Unless somebody has a better idea, I'm going to start
using the term "thermal energy" to the exclusion of the word "heat".  Sears
and Salinger might claim it is imprecise to say "work is converted to heat"
but they can't stop me from saying "nonthermal energy is converted to
thermal energy."

I'd like to make this retroactive, in the following sense:  if anybody
found my previous notes incomprehensible, please re-read them after
replacing every occurance of the term "heat" with the term "thermal energy"
and see if they make more sense.