From: "JACK L. URETSKY (C) 1996; HEP DIV., ARGONNE NATIONAL LAB, ARGONNE, IL 60439" <JLU@hep.anl.gov>
Date: Sat, 20 Jul 1996 21:07:37 -0500 (CDT)
Hi Gene-
You ask:
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What point are you trying to make? From your previous
response I was felt were kindly supplying a concrete example
supporting my earlier statements that criticized the equation F =
dp/dt = m dv/dt + v dm/dt. Now I'm unsure of your intent.
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I wanted to sharpen the point. Perhaps a better way
to have done it would have been to ask for, or do, a derivation
of the rocket equation. Surely it involves d/dt(mv). No?
The sand leaking out of the wagon doesn't "really"
involve a change of mass. What is happening is that the mass is
just occupying a greater volume as it spreads itself out (until
it gets to the sidewalk -when there is no interaction with the
wagon). The mass "change" for the rocket is that a part of the
rocket's mass changes its velocity relative to the remainder of the
mass.
Regards,
Jack