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Re: There's work, and then there's work



(Oops, somehow that last message got "formatted." Let me try again ...)

Eric Lane wrote

Where can we find definitions of

0) the microscopic mechanical work
1) the mechanical pseudowork, which at least
one person calls work, as I discovered
yesterday.
2) the thermodynamic "W" work.

Joel has provided a reference to my paper with Harvey Leff. I would add that

1 an "executive summary" of the results of that paper is
available at

http://www.csupomona.edu/~ajm/special/aaw_excerpts.pdf

2 in that summary, I would identify

a) "microscopic mechanical work" with what we called
"frame-specific total work" -- W_tot

b) "mechanical pseudowork" with what we simply called
"pseudowork" -- W_ps

c) "thermodynamic work" with what we called
"system-specific external work" -- w_ext

The last identification is the slipperiest because thermodynamic work
itself is a somewhat poorly defined quantity. This, in turn, is
because "internal energy" is a somewhat poorly defined quantity. In
thermodynamics applications the "internal energy" of a system
consists of those parts of its energy that we care to concern
ourselves with. Just for instance, sometimes we care about the "bulk
translational KE" ( = "center of mass KE" = "pseudoKE") and sometimes
we don't. (I'd say *usually* we don't, but not without fear of being
challenged.)

Finally, I won't try to defend our often ponderous names for the
seven different worklike quantities that we discuss in this paper
except to reemphasize how critically important it is to distinguish
very carefully between them. As John Denker wrote:

"With such messed-up terminology, it's a wonder that
anyone is ever able to communicate with anybody."

I couldn't agree more and the astonishingly tortured history of the
Work/Energy threads on phys-l serves as powerful testimony to this
fact.

--
A. John Mallinckrodt http://www.csupomona.edu/~ajm
Professor of Physics mailto:ajm@csupomona.edu
Physics Department voice:909-869-4054
Cal Poly Pomona fax:909-869-5090
Pomona, CA 91768-4031 office:Building 8, Room 223