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Hi all-
This "accident" is not really an accident. The so-called
equivalence principle is a definition. We define Newton's constant G so
that the inertial mass for some element equals the gravitational mass.
The "accident" is that when you do the definition for one element (or
substance - however you want to define it) it holds true for all
substancees, as demonstrated by the Eotvos experiments. It is the ratio
of gravitational to inertial mass that is constant for all substance (se
Weinberg, Gravitation, Sec. I.2), and this ratio can be made unity by a
suitable definition of G (big G).
This point seems to be missed in the discussion in Halliday &
Resnick (3d Ed.) and, perhaps, in other elementary texts. Feynman doesnt
stress the point in his Lectures, although, characteristically, he sort of
sneakss up on it.
Regards,
Jack