Without wishing to deny the correctness of everything Bob Sciamanda wrote
in his "MET" exposition, I would like, (once again), simply to point out
that this theorem has often been referred to in the literature as the
"pseudowork-energy" theorem or some minor variant thereof.
I don't see any reason to avoid the use of the perfectly good word,
"work," but I think it *is* useful to reserve its meaning for the line
integral of the scalar product of a force with the displacement of the
point at (or the specific particle on) which the force acts. Doing so and
then summing the works done by various combinations of 1) all internal
forces and 2) all external forces as calculated within either 1) an
inertial frame or 2) the (possibly noninertial) system CM frame yields
five (count'em five!) different *and* useful "work-energy theorems."
Of course, it is also worthwhile to consider the line integral of the
scalar product of the net external force with the displacement of the
system CM--that is, the work that *would* have been done *if* the net
external force had been applied at that point. When one does so one gets
another useful relationship (that which Bob is calling the MET) that looks
like a work-energy theorem, but is not (because the quantity calculated is
*not* a work by the definition proposed above for that word.) By calling
this work-like quantity "pseudowork" we avoid all further difficulties and
we can then simply speak of the "pseudowork-energy" theorem and the five
different "work-energy" theorems.
John
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A. John Mallinckrodt http://www.intranet.csupomona.edu/~ajm
Professor of Physics mailto:ajmallinckro@csupomona.edu
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