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Date: Tue, 23 Feb 1999
Relativistic Mass
Thomas M. Miovas, Jr.
While I agree that it is improper to define "mass" as "quantity
of matter," I was never taught that this is the way Newton
defined the term. In my research to find Newton's definition of
"mass," it is always defined as "quantity of resistance to
change of motion" (or "quantity of inertia"). This is the way it
is defined in the three physics text books I have at home, and
on the web under searches for Newton and mass. Could you provide
a reference to Newton specifically that defines "mass" as
"quantity of matter"?
The problem with defining "mass" as "quantity of matter" is the
implication that elementary particles (electrons, protons,
neutrons, etc.) are made of various numbers of smaller particles
each having the same mass. For instance, a proton is much more
massive than an electron, so to have the mass it has one would
have to say it is made up of many more "primary" constituents
than the electron (which may be why Lewis made his comment about
Aristotle's prime matter). However, there is no evidence for
this whatsoever.
I prefer the "resistance to change of motion" formulation, and
so I am not against the idea of relativistic mass (which is not
to say I agree with every aspect of Relativity). At high enough
(relative) velocities, it simply becomes more difficult to
change the motion of a body (including particles), which is my
understanding of that aspect of Relativity.
