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Re: F=ma; new strain...



At 17:38 -0700 11/14/03, Nathaniel Davis wrote:

Mass (the "amount" of something) is directly connected to the force of
gravitational attraction: Weight.

We also define mass according to the measure of inertia, i.e., more massive
objects "carry" more inertia.

I remember my college professors constantly alluding the fact that inertial
mass is always equal to gravitational mass. But why is this true? Wherein
lies the equivalency? The "inertial mass" should be completely independent
of a gravitational field, right?

How can I explain this to my high-school students?

It seems to me that the best tack to take is to admit that we don't
know why (there may be some reason deep within general relativity,
but I've never heard of one). I treat it as more or less just
something that seems to be. I point out that there seems to be no a
priori reason why it should be so, and that, for new students, it is
at best a mixed blessing, because it makes it too easy to forget
about the effects of mass, when mass keeps cancelling out of the
gravitational equations. Then I point out that charge, which I
sometimes call "electrical mass" by analogy with "gravitational mass"
sometimes I call gravitational mass "gravitational charge" just to
make the point) doesn't cancel out of the equations like
gravitational mass does (example mg=ma, and qE=ma). For electricity,
the "charge to mass" ratios of the elementary particles can be any
number of different things, but for gravity, it appears that the
"charge to mass" ratio is always exactly one, for anything.
Conjecturally, I speculate that perhaps this quirk of matter has
something to do with the fact that we have so far been unsuccessful
at creating a quantum theory of gravity.

One of the remaining mysteries. Maybe this too can be explained by
string theory.

Hugh
--

Hugh Haskell
<mailto:haskell@ncssm.edu>
<mailto:hhaskell@mindspring.com>

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