🚀 go-pugleaf

In article <1992Jul22.193837.18095@sfu.ca> palmer@sfu.ca (Leigh Palmer) writes:

> "Mass" as you use it
> is equal to neither inertial nor gravitational mass as those terms apply to
> any system more complicated than a particle at rest!

There is, however, *nothing* which is equal to either inertial or
gravitational mass for a relativistic body.

That is: I define the inertial mass of a body as the "m" appearing in
the equation
		F = m a,					(1)
and I define the gravitational mass of a body as the "m" appearing
in the equation
		F = G m M / r^2.				(2)
I believe that these definitions are customary; I don't know what
other meaning could be attached to the phrases "inertial mass" or
"gravitational mass."

Both of these equations are true in nonrelativistic physics, and
neither equation is true in relativistic physics, no matter how "m" is
defined.  Relativistic gravity, in particular (i.e., general
relativity) is much more complicated than Eq. (2) would suggest.

Note that this fact has been known since the earliest days of
relativistic physics.  Around the turn of the century, some physicists
used to write Eq. (1) using two different "masses," the "longitudinal
mass" and the "transverse mass," which differ by a factor of gamma.
For reasons that I do not understand, one of those "masses" was
subsequently called the "relativistic mass," and the other one was
dropped from the discussion.
--
Matthew Austern              I dreamt I was being followed by a roving band of
(510) 644-2618               of young Republicans, all wearing the same suit,
matt@physics.berkeley.edu    taunting me and shouting, "Politically correct
austern@theorm.lbl.gov       multiculturist scum!"... They were going to make
austern@lbl.bitnet	     me kiss Jesse Helms's picture when I woke up.