Re: are normal reaction and tension conservative ?

[brian whatcott <inet@INTELLISYS.NET>]

At 08:46 6/30/01 -0700, John Mallinckrodt wrote:
> On Sat, 30 Jun 2001, Chetan wrote:
>
> > are normal reaction and tension conservative ?
> >
> > I think it depends on what forces are causing the normal reaction and
> > tension(like when two masses are hanging on the opposite sides of a pulley
> > then the tension in th rope is due to gravity which is a conservative force
> > and so the tension is conservative).
> >
> > Is this right?
>
> No, but this is a good question--the type only an uncommonly
> thoughtful student would be likely even to think of.
>
> ... real ropes and real surfaces are generally at
> least somewhat "dissipative."  They exert forces that are not
> completely calculable from their configurations and may exhibit
> hysteresis and/or velocity-dependence.  For instance, a rope may
> (and usually does) exert a stronger pull at each specific length
> while being extended than when it is subsequently allowed to
> relax.  As a result, the work done *by* an external agent to
> extend the rope is smaller than the work done *on* the external
> agent as it is allowed to relax.
>
> John Mallinckrodt      mailto:ajm@csupomona.edu
> Cal Poly Pomona          http://www.csupomona.edu/~ajm


John's meaning though inadvertently reversed, was perfectly clear
from the context of the rope/work hysteretic example.
Moreover, I learned something about the idea of transferring a
conservation concept onto one of its constitutive components.
[There is even a word for this in literary and poetic contexts.]
 Most important, I applaud his sympathetic treatment of the
question.

brian whatcott <inet@intellisys.net>  Altus OK
                Eureka!