There is a problem here in that there are actually two definitions of "inertial mass". The first comes from the special relativistic formula M
rel = E/c
2, where E
2 = p
2 c
2 + m
o2c
4. Frankly, I have never liked this but you see it all the time in elementary textbooks.
The other definition is related to the acceleration of a mass due to a force, such as an electric force or the force of gravity. The main issue is whether two different types of material, such as gold and aluminum weighing the same amount on a scale, have different values of acceleration under a gravitational force. The answer, epitomized by the Eotvos experiment, (see
http://en.wikipedia.org/wiki/E%C3%B6tv%C3%B6s_experiment) is that there appears to be no difference between two different kinds of material. Hence the term "Equivalence of inertial and gravitational mass".
Yes, general relativity does give corrections to a 1/r
2 gravitational force law but it doesn't allow for velocities equal to or greater than c for a particle with a finite rest mass.
LeeH
(published on 07/10/2008)
