Re: Center-of-mass system

[THOMAS SANDIN <sandint@NCAT.EDU>]

        We're back to another problem resulting from the abolition (by
some) of relativistic mass. As I explained on page 1033 of "In Defense of
Relatistic Mass" (Am. J. Phys. 59 (11), November 1991), "The center of
mass of the system is its center of relativistic mass. However, we can
reconcile both points of view by referring to the center-of-momentum frame
rather than the center-of-mass frame. In the center-of-momentum frame, the
total momentum is zero and the center of relativistic mass is at rest for
particles that only interact through contact forces."

        Those conservation laws do NOT hold in general for the
center-of-invariant-mass frame.

                                                Tom Sandin

On Thu, 13 Apr 2000, Laurent Hodges wrote:

>         I checked over an exam question written by a younger colleague, who used
> the term "center-of-momentum system."  I objected, saying it could be
> "center-of-mass system" or "zero-momentum system" but not
> "center-of-momentum system,"  which sounds nonsensical to me.
>         Checking with other faculty I found two other young faculty who liked
> "center-of-momentum system" and preferred it, telling me it was common, and
> two older faculty who considered it an abomination and only really liked
> "center-of-mass system."  All four of these faculty are researchers more
> than teachers in their interests.
>         Comments?
>
> Laurent Hodges, Professor of Physics
> 12 Physics Hall, Iowa State University, Ames, IA  50011-3160
> lhodges@iastate.edu   http://www.public.iastate.edu/~lhodges