Re: Definition of heat [and S]

[Jim Green <JMGreen@SISNA.COM>]

OK Ludwik, the requested corrections follow:

At 07:50 AM 27-11-99 -0500, you wrote:
> Let me paraphrase JohnD (see below) in order to be corrected,
> if necessary.

People are free to "define" any word any way they want; it then becomes a
problem of being understood.  IF, by "heat" one means the Q in the First
Law then see the corrections below.  If one wants to use the word in some
other way, then it would be very hard to discuss the First Law:

> There are no advantages in emphasizing that heat is "energy in
> transfer".

Not only is there no advantage, it is just plain wrong.
Further it is not correct (but very commonly done) to talk about "energy as
being "transferred" if by "transferred" one is implying motion.  "Energy"
does not move.

Now in some other discussion short hand language might be used but not here
in this topic.

> Heat is a form of energy.

"Heat" (if by "heat" one is referring to Q) is not in any way a form of
"energy".  "Heat", ie Q, is an action that might be _done_ to a
system,  Just as "work" is something that might be _done_ to a system.

> Thermal energy is heat.

"Thermal energy" is an awkward phrase at best -- or at the very least
clouds the issue -- if what is meant is "internal energy" - If that is not
what is meant it is surely useless.

And "heat", if Q is inferred, is most certainly NOT "energy"

> It is not wrong to say that the heat lost by an object A is later
> present in objects B or C. The caloric analogy is not totally
> wrong. Heat can flow but it is not a material substance.

Saying "heat is lost" reifies  [Leigh's favorite word] the concept of
"heat" and is not a valid.

The "caloric" analogy is _always_ "totally wrong".  It may be useful as
short hand, IF in the lecture/discussion it is made patently clear that
this anachronistic analogy is being used.  (Note btw that Carnot had
suspicions that the prevailing concepts were wrong, but he had other things
on his mind and did not investigate it further.  And Rutherford was simply
ignored.  He still is to a large extent.)

> There are more important issues to deal with; some students
> are not aware of the fundamental difference between heat and
> temperature.

Some _instructors_ are not aware of the difference!!!  That is why we have
the annual discussion -- but it might appear that we are back in the 80s
when this discussion began.

It is also true that instructors should not teach anything false just for
the effect of making it "understood".  If you are not able to say it
correctly, don't say it at all.

> Trying to avoid dS=dQ/T may be challenging to
> some creative thinkers but many teachers are used to it. They
> need to be persuaded to abandon this macroscopic approach.

Even if one could tell us just how to determine DQ, dS=DQ/T is still not
always valid.  For example, in the Joule experiments, the traditional of us
would say that DQ=0, but dS is NOT 0.

This is where we left this discussion of a few weeks ago: How does one
partition the various actions laid upon the system between DW and DQ?

(BTW I really like the word "partition" here, but I am not sure who first
used it.  I think that I know, but I don't want to credit the wrong person,
so could the praiseworthy party please tell me privately. TX)

In the above regard it can be said with certainty that DQ is NOT always
dependant upon a temperature difference between some sort of thermal
reservoir and the system, IF DQ has anything to do with S.

Please note that _I_ did not bring up the topic of  the evil four-letter
word this time. (:-)

Jim Green
mailto:JMGreen@sisna.com
http://users.sisna.com/jmgreen