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Path: utzoo!watmath!clyde!bonnie!emh
From: emh@bonnie.UUCP (Ed Hummel)
Newsgroups: net.physics
Subject: Definition of mass in relativistic mechanics
Message-ID: <576@bonnie.UUCP>
Date: Sun, 6-Oct-85 08:39:56 EDT
Article-I.D.: bonnie.576
Posted: Sun Oct  6 08:39:56 1985
Date-Received: Mon, 7-Oct-85 02:57:27 EDT
Organization: AT&T Bell Laboratories, Whippany NJ
Lines: 26


	I have a question about semantics.  The concept of mass in
relativity is substantially different from the Newtonian view.  Yet, for
convenience, the word has been kept.  Most texts (even recent ones)
and all the early papers use the result (definition):

		mass = gamma * (rest mass).

This  is consistent with keeping the Newtonian formula for momentum.
	Most of the professional physicists that I know, do not use the
word "mass" according to the above definition, but use it to mean "rest
mass".  The preferred usage seems to be to redefine momentum:

	momentum = gamma * mass * velocity.

Where mass is understood to be "rest mass".  Of course, the same goes
for energy:
	E=m*c**2	->	E=gamma*m*c**2.

I would like to hear opinions about:
	What usage is more common?
	Are there good reasons for preferring one definition over the other?
	What exactly is the role of "inertia" in relativistic mechanics?

-------------------
Ed Hummel