Re: [Phys-l] momentum and energy

[Jack Uretsky <jlu@hep.anl.gov>]

What's the definition of "in"?  I define "conserved in the collision" to 
mean the same before and after.  The definition becomes a bit hazy in the 
case of coulomb (and gravitational) collisions where there is no sharp 
"before" or "after" - an interesting physics point to which your students 
can be introduced.  Many years later one of them will say "My gosh, this 
is the infra-red problem!!!!"
				Regards,
					Jack

On Tue, 14 Nov 2006, Ken Fox wrote:

> I hate to be fussy (but this is Phys-l afterall ;-)) about "conserved in the
> collision" but the KE is the same immediately before and after but not
> during. The deformation of the objects during the collision allows for a
> form of PE.
>
> Ken Fox
>
> On 11/13/06, Jack Uretsky <jlu@hep.anl.gov> wrote:
> > I suggest that the definition of "elastic collision" be that kinetic
> > energy is conserved in the collision.  This definition agrees with
> > accepted practice in every frame, classicly and quantum mechanically.
> >                                         Regards,
> >                                                 Jack
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