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Re: Non-conservative forces



Carl wrote:
| > The force is not a function of position.
| > I would like to add this as a requirement for a force to be
| > conservative.
John D answered:
| Well, Carl is consistent in his terminology.
| Other folks use different terminology.

I agree with Carl.
In the traditional Newtonian Mech course, the student learns that if the force
on a particle is simply a function of the particle's position, AND if the line
integral of that force is path independent, THEN the force function can be
written as the (negative) gradient of a scalar field - the potential function
(with energy units). There is then a constant of the motion: the sum of the
kinetic energy of the particle and the potential function of the particle's
position. Because this sum is constant (conserved) the student is taught to
call this type of force (a zero curl, vector function of only position) a
"conservative force". I think the word "conservative" as applied to forces,
should be restricted to only this meaning. Indeed, in other fields such a zero
curl, vector field is also called a "conservative function" or "conservative
vector field" (eg.: a velocity field in hydrodynamics or meteorology).

It may be useful to speak of conservative SYSTEMS with a wider use of the term
"conservative" (non-dissipative); but "conservative force/field " is a term with
a well established and restricted mathematical meaning.

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor