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