Re: Re FLOW of energy

[Leigh Palmer <palmer@sfu.ca>]

Bob Sciamanda said:

> If physics had always appreciated the molecular basis of "thermal
> energy", so that caloric had NEVER been proposed, we would feel
> free to speak of the flow of heat just as glibly as we now speak
> of the flow (or transport, or velocity, or propagation) of so many
> other non-substantial (and even purely mathematical) entities
> without outcries of "heresy!" from our colleagues.

Those of us who know what the word means might agree with you, but
the physics professor should not speak glibly when talking about
thermodynamics, *ex cathedra*, so to speak. Certainly no one should
disagree with that proposition.

I have no problem with the term "thermal energy" used carelessly.
It should be recognized, however, that there is no definition of
this term that is recognized by a large fraction of the physics
speaking world. The thermodynamic potentials, of course, are well
defined. The term "heat content", used here in BC in high school
chemistry, is one which I abhor.

> I strongly recommend the (laborious) reading of Bridgman's "The
> Nature of Thermodynamics" (Harper Torchbooks, 1961) in which the
> "flow" of all sorts of things is examined.  This includes the
> flow of heat, the flow of mechanical energy within stressed,
> moving structures (a highly useful - perhaps indispensable -
> model in mechanical engineering), the flow of entropy (which can
> even increase in total quatity as it "flows"!), etc.  He also
> examines the block sliding over the plate! Also criticized is
> the notion of describing entropy as a measure of "disorder"!

Bridgman's philosophy is pretty heavy going. I've ranted against
the dismissal of entropy as a measure of disorder in here before.
Your citation of his treatment of the "flow" of mechanical energy
almost (but not quite) moves me to look at what he wrote. Did you
not understand my treatment of that topic? As for the flow of
entropy, that construct is entirely analogous to the flow of energy.
One *can* calculate such a quantity (entropy flux), but it lacks
the reality possesed by charge and mass (new definition). It isn't
even conserved in general.

Leigh