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Re: Kinds of Mass



Hi all-
In response to Rick Tarara:
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I guess I don't understand why we hold onto the dual nomenclature. Yes the
conceptual origins suggested there might be a difference, but it seems that
the experiments are pretty convincing that inertial and gravitational mass
are identical. Why continue to speak of these separately? Are they ever
different? For example, what is the gravitational interaction between two
masses moving parallel to each other (relative velocities zero). Would one
use the rest masses or the relativistic masses in GMm/R^2 (realizing that
true relativists would probably never use the Newtonian formulation) and
does it matter in terms of the inertial/gravitational nomenclature?

Rick

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If it were true that all substances experienced the same force from
some standard mass (the Eotvos experiment), then the equality of gravitational
and inertial mass would be a matter of definition. We would be free to choose
units for which equivalence it true (see Weinberg's book on gravitation where
he discusses the "weak" equivalence principle).
The difficulty is that the Eotvos experiment, as is true of any experiment,
only establishes substance independence of gravitational force within a range of
uncertainty. It is possible in principle, then, that some future experiment will
find a small, but non-zero difference, between, say, the gravitational accelerations
of a K-meson and a proton in the gravity field of the earth. We would then have
to drop the "strong principle of equivalence" and distinguish between the
gravitational and inertial masses of some substances. There will be standard
substances for which gravitational and inertial masses will be equal by
definition.
Regards,
Jack


"I scored the next great triumph for science myself,
to wit, how the milk gets into the cow. Both of us
had marveled over that mystery a long time. We had
followed the cows around for years - that is, in the
daytime - but had never caught them drinking fluid of
that color."
Mark Twain, Extract from Eve's
Autobiography