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Re: Why do we care about heat?



I stand by this statement. Heat and work are modes of energy transfer
into the defined system. As long as the total increment in the system
energy is correct (dE=dQ+dW) the final system state will be correct, as
will be all state variables, including the entropy. Note that the entropy
change is calculated as dQ/T for a reversible path (not the real path
which is here under contention).

Bob

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor

----- Original Message -----
From: Leigh Palmer <palmer@SFU.CA>
To: <PHYS-L@lists.nau.edu>
Sent: Monday, November 01, 1999 2:41 AM
Subject: Re: Why do we care about heat?


The bottom line is that it does not fundamentally matter how you
(legitimately) divide up dw and dQ, as far as the answer to any real
physics/engineering question is concerned - as you illustrated in the
various interpretations of your inelastic collision example.
Rutherford
would say that these arguments are about stamp collecting (taxonomy),
not
physics. I think this flexibility should be part of our teaching, just
as
a history teacher should admit of another "ratio divisionis" (other
than
his) of civil war causes, to his students.

Now just a darn minute there, Bob! Are questions about entropy
real physics/engineering questions? Does the name of an engineer
called Sadi Carnot bring any applications to mind?

It certainly does matter that one understands the difference
between work and heat. I'm sure you know that. I think you got
carried away with the spirit of the arg-, er, discussion. I
think I know what you mean, but this statement is too strong.

David Bowman may jump up and down and disagree with what I'm
about to say, but the classical meaning of entropy is the one
which is fundamental here. One can certainly prove that the
Boltzmann interpretation set in a quantum mechanical frame is
also correct, but the first applications of the concept were
to engineering and chemical problems. Solution of such problems
relies heavily on the distinction between heat and work in
ideal models.

Leigh