Re: elastic collisions

[Bernard Cleyet <anngeorg@PACBELL.NET>]

"...  My recommendation is consistent with the usage in
atomic physics, where a collision that leaves one
of the molecules in an excited rotational state is
considered inelastic."

Or any excited state, à la Frank - Hertz?

bc


"John S. Denker" wrote:

> Jeff Weitz wrote:
> ...
> > elastic collisions, which are usually defined as collisions
> > that conserve total kinetic energy, or so I've always thought.
>
> OK for point particles ....
>
> >  Now we have an august textbook that defines elastic collisions
> > as collisions in which, "in the cm frame, the velocity changes
> > in direction, but not in magnitude."  (p129) Later, in the discussion

cut

> My recommendation is consistent with the usage in
> atomic physics, where a collision that leaves one
> of the molecules in an excited rotational state is
> considered inelastic.
>
> I am aware that some people, especially in elementary
> texts, use "elastic" as a synonym for "nondissipative"
> but I don't recommend that.  And in particular you
> should !!not!! try to come up with an elementary
> mechanical definition of nondissipative.  Many people
> have tried and failed.  Dissipation depends on entropy.
> You can't derive entropy from energy or vice versa.
>
> This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.

This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.