Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Work-Energy or Work-Kinetic Energy??



John Mallinckrodt wrote:
. . .
I would like, however, to weigh in on the slippery concept of
potential energy due to the work done "on" a system by "a"
conservative force. Potential energy is a property *of* a system
and, must properly be considered as an *internal* energy that
arises from *pairs of internal* forces, NOT *single external*
forces.

All forces are "half interactions" and we should really speak of
the potential energy due to conservative "interactions." In the
cases of the gravitational and electrostatic interactions between
point particles, the interaction generally does work on *both*
particles and it is the sum of those works that depends only on
the initial and final separations of the particles. We designate
the interaction "conservative" as a result of this fact, and
assign a potential energy to the interaction. That energy belongs
to the system consisting of *both* particles and can not sensibly
be allocated between them.
. . .
John


All of this is written in the spirit of the energy concept implied by
the FLT, and I agree with every word! However -

In further development of the WET (as I have stated it) it is found
that a force whose curl is zero can be derived from the gradient of
a scalar potential function (I won't even call it energy, though
those are its units), and that the line integral of this force (I
won't even call it work) can be evaluated as the difference in the
values of this potential function. Yes, the FLT "energy" is best
thought of
as a property of both interacting things, but it is certainly
legitimate
and very useful to consider the force on the thing of interest as
calculable
from a potential function. (In fluid flow, the fluid velocity is
often calculated as the gradient of a potential function - and not even
the
UNITS or NAME of energy occur here.)

The WET is simply a useful calculational
tool that says no more than F=ma. The problem is that it uses the words
work and energy, which other investigations have given different
meanings.
I think in time I will bore you with an expansion of that idea {:]
-Bob
--
Bob Sciamanda sciamanda@edinboro.edu
Dept of Physics sciamanda@worldnet.att.net
Edinboro Univ of PA http://www.edinboro.edu/~sciamanda/home.html
Edinboro, PA (814)838-7185

"We are usually convinced more easily by reasons we have found ourselves
than by those which have occurred to others."
Blaise Pascal in "Pensees", 1670.