Re: What Flows?

[Jim Green <Jim.Green@Snow.edu>]

Well, Leigh, I do know that we are close in these views -- closer that many
others on the list, but still there are divergences (:-)

At 10:00 PM 9/8/96 -0700, Leigh wrote:

> You've lost track of who's on which side. Heat does not flow. 

We certainly agree to this point.  And I sorely wish that we, together with
those of like mind, could blot out the caloric language from every physics
text and teacher in the galaxy.  Let us continue in this effort.

But there may be differences still:

>                                                 Heat is 
> the name of any process by means of which energy is transferred from
> one system to another with no resulting change in external coordinates
> of either system. Work is the name we give to any process by which
> energy is transferred from one system to another by means of changing
> the external coordinates when the systems are themally isolated from
> one another. 

OK, Leigh, let's ask some more questions -- let's go back to the Parable of
the Cylinder: The cylinder with adiabatic piston, adiabatic sides and
diathermal bottom sits on a hot plate; it has a diathermal window with
propane flame, an internal propeller with external crank, and internal
resistor and external battery,  Which mechanism does "work" and which *does*
"heat".  (From your statements I assume that you might agree to the language
"do heat" so as to clarify that "heat" is not a substance which flows. --
but alas you know where I am going -- bear with me for a sentence or two.)    

> We say "energy flows" from one system to another; 

Leigh, *I* never say "energy flows" *it* isn't a substance any more than
"heat". I *would* agree to your compromise language of "energy is
transferred" -- that would be fine -- as in I transfer money from one bank
to another, but the money doesn't "flow" -- dollar bills don't move.
(Analogies are tenuous at best -- this will have to do for now)

>                                                               we never
> say "work flows", and we *should not* say "heat flows". 

Again we are in total agreement here

>                                                      That is the
> conventional assignment of meaning to those words. If you do not wish
> to use those terms that is your choice, but you do students a great
> disservice by teaching them language that other physicists do not use.

Well. Leigh, I fear that, unfortunately,  this *is* the conventional
language -- I agree that it is evil, wicked, mean, bad and nasty -- however,
most on this list use it and almost every text does as well.  Indeed, some
on this list take great umbrage at the suggestion that this usage is faulty.
Texts dutifully cite Rutherford and denounce the idea of "caloric" and them
in the next paragraph go right ahead and use this misleading language and in
the process confuse the begeebers out of students and instructors alike --
after all last year's students are this year's teachers.

Folks, what Leigh is saying, I think, is that in T#1: dU = DQ + DW,  the "Q"
is an external action -- and that we all call this "heat", but at the same
time we say that "heat" is inside the body - that "heat" "flows" (yuch) into
the body. I agree that this is clearly wrong!  The thing that is inside the
body is "internal energy".  We can "heat" (verb) the body or "do heat" to
the body, but HEAT DOES NOT FLOW -- unless of course we would all agree to
call the internal energy "heat" and then call "Q" something else -- say
"elephant" -- no, that word is already used up for those gray things -- we'd
have to find another word.  But we should NOT just use the same word for "Q"
and for "U".

Leigh, the above is where we agree for the most part.  Now I'd like to take
the next step:

> > 2)  Can you tell me how it is that the cool object increases in energy with
> > out saying the words "heat" and "flow"?  What is the detailed mechanism?
>
> Say that energy flows. 

I would never say this in public -- especially where children could hear. (:-)

>                       Who cares what the "detailed" mechanism is? 

Leigh, you are waving your hands; it *does* matter what the mechanism is! If
you would answer the question, I could show you how it does matter.  (Inded,
I think if you would consider the question and answer it, I would not have
to show you (:-))  I have already said it in my words (in private e-mail),
but it doesn't look like I am making sense to you.  You say it in *your* words: 

Consider two adjacent bodies (A and B) with adiabatic walls except for the
adjoining wall which is diathermal.  Say the diathermal wall serves only to
keep A molecules from entering B and vis versa, but nevertheless A heats B.
Or consider piece of steel A and abutting piece B - where A heats B.  How
might that happen? 

Don't weary, Folks, we'll get this sorted out shortly.



Jim.Green@Snow.edu