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Re: Why work before energy in texts



Joel has a reservation about "energy = ability to do work'.
He is not objecting to it in the context of the idealized
world in which all forces are conservative. Let us wait
till the next model and then ask if the above generalization
is acceptable. I am glad that we debate the vocabulary of the
simple model before using it in a more sophisticated model.
The thread "ENERGY WITH Q" is likely to be controversial.

"RAUBER, JOEL" wrote:


PEgrv==work done against a weight (or -work by wieght)
PEspr==work done against a spring (or -work by spring)
PEelctr==(later) is work against the electric field.
In general work done against a conservative force
BECOMES POTENTIAL ENERGY ASSOCIATED WITH THAT FORCE
(energy=ability to do work). Is this acceptable or not?
Ludwik Kowalski

This seems perfectly acceptable to me, (except perhaps the energy=ability to
do work, for thermo reasons), i.e. we may define potential energy for a
conservative force in terms of the work done by that force; despite the
following quote:

"BOTTOM LINE: Defining work in terms of potential energy is a
blunder. Defining potential energy in terms of work is an even bigger
blunder."

Many respected authors do this of course, (define potential energy in terms
of work)

E.g.
Feynman chapters 13 and 14 Vol. 1
Goldstein page 4, 3rd ed.
Arnold page 15
Marion 4th ed., page 79

. . . ad nauseum

Joel Rauber