Re: [Phys-L] Compressed air and thermodynamics

[Dan MacIsaac <Dan.MacIsaac@NAU.EDU>]

On Tuesday, July 26, 2005, at 03:16 AM, Leigh Palmer wrote:

> There seems to be some considerable confusion over the "amount of
> potential energy stored in a tank of compressed air". Let's discuss
> this!
>
> First, note an important quotation from the Chairman: "There are no
> blocks" (Richard Feynman "Lectures on Physics", Ch. 4). I note that
> no one has ever observed potential energy in its naked state,
> independent of the system to which it pertains.

Actually, Gene Hecht and Ruth Chabay + Bruce Sherwood have written some
really interesting, relevant and informative notes on this topic.

See Hecht's Nov 2003 TPT Article "An Historico-Critical Account of
Potential Energy: Is PE Really Real?" which  comes to the conclusion
"...that PE is as real as mass is real." (Abstract)

See the C&S talks on energy, esp "The zero of potential energy is not
arbitrary" at
<http://www4.ncsu.edu/~rwchabay/mi/mi_docs.html>

These papers discuss relativistic considerations to potential energy
and invoke a need for consistency with relativistic constraints even in
classical mechanics, which constrains potential energy much more than
we typically do in standard introductory mechanics treatments.  We use
limited historical models of PE for traditional reasons, perhaps
avoiding modern physics ideas overlong in teaching intro physics.

Whether these considerations are "independent of the system" is to be
determined by having Leigh defining the system he has in mind.

Dan MacIsaac, Associate Professor of Physics, SUNY-Buffalo State College
222SciBldg BSC, 1300 Elmwood Ave, Buffalo NY 14222 USA 716-878-3802
<macisadl@buffalostate.edu>  <http://PhysicsEd.BuffaloState.edu>
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