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Re: FLOW of energy



I agree with the gist of Ludwik's comments below. It seems to me that most
of the 'incorrect' usage (as so vehemently opposed by Jim) surrounding the
word 'heat' involves just this attempt to describe intermediate macroscopic
phenomenon. OK, microscopically the three methods of 'heat transfer'
(conduction, convection, and radiation) might boil down to work being done,
but the image of energy being transferred through a kind of flow mechanism
is NOT going to do serious harm to the intellectual well-being of most
physics students (90% plus of whom will not progress to a thermodynamics
course).

I challenged Jim to explain how the combusion of coal in an electrical
generation plant ends up as a rise in temperature in a power line without
using heat/energy transfers, flows, heat as energy, and all his other
taboos, in a clear, concise way that would be appropriate for intro
students. I think I can do it reasonably well using the 'forbidden' terms
and in so doing increase student's understanding of the physical world
around them. Could these students be taken to a deeper understanding, one
based on thermodynamics? Sure, some could, but for the majority, what is
gained? If we are only to teach what is absolutely true then we can teach
NOTHING. If we are only to teach the most current version of the 'truth'
then we need to throw away all the intro texts books, and start with
quantum mechanics, QCD, general relativity, statistical mechanics (why even
bother with Classical Thermo?) and the like. If you want to reduce your
class sizes, feel free to adopt such an approach.

I'm willing to look at text books that treat all the various 'heat' topics
correctly (according to Jim) if they can do so in a way that is as
teachable, as learnable, as meaningful to intro students as current texts.
Feynman (given as an example in another note by Jim) is NOT accessible to
intro students--I know, it was used as my intro E&M text back in '65 and I
was totally lost (the really smart kids got themselves a copy of R&H {the
names were flipped back then} in order to learn the basic material).

So ultimately the argument would be that although the use of 'heat' as a
label for a form of energy, energy transfer, energy/heat flow are not
accurate descriptions of the microscopic processes and the nomenclature is
at odds with Classical Thermodynamics, they CAN be useful in describing the
macroscopic behavior of systems and CAN improve the student's understanding
of such phenomenon. Leave the nitpicking and microscopic descriptions for
advanced courses. If the proponents of a 'purer' physics for intro
students can provide models (that work) for teaching the whole range of
phenomenon now done 'incorrectly', then more of us might join the crusade.

Rick



----------
From: LUDWIK KOWALSKI <kowalskil@alpha.montclair.edu>
To: phys-l@atlantis.cc.uwf.edu
Subject: FLOW of energy
Date: Saturday, August 30, 1997 10:00 AM

In one of his postings yLeigh said that "the energy is not stuff. It
doesn't flow because it can't be localized, and treating it as stuff
leads to well-known problems (that's what the caloric model was)".
Jim also argued against the phrase energy flow. "There is nothing that
flows", he wrote. "There is no so called heat flowing! In fact there is
no energy flowing either! What happens is WORK IS DONE! In each case!"
He was referring to six mechanisms through which internal energy of a
gas could be increased in a container. Placing the container on a hot
plate was one of the mechanisms.

What is the proper name for the quantities expressed in W/m^2 ? What is
wrong with saying that energy flows from a broadcasting station to the
antenna of my radio set? Or consider a disturbance, for example a single
pulse, moving along a stretched slinky.

Jim's argument was that the so-called "heat flow" is really nothing else
but numerous transfers of energy from faster molecules in the plate to
slower molecules in the gas. Kinetic energy of gas molecules increases
(on the average) because work is done on them through collisions.

A very good observation. But what is wrong with saying that a large
number of individual collisions leads to a collective property - flow of
energy. It is like the law of supply and demand; the law does not apply
to individual transaction, it can only be used to understand some market
situations. I consider thermodynamics to be a macroscopic science. As
we all know, temperature and pressure are collective properties; these
concepts do not apply to individual molecular interactions.

Ludwik Kowalski