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## Main Question or Discussion Point

In physics as a general discipline, there are 2 types of mass gravitational and inertial which have different definitions but experimentally they have turned to be extremely similar, 1 part in 10^12. Moreoever, general relativity predicts they are equivalent. They are all measured by an observer observing the masses accelerate in space.

However, in SR where all objects move with constant speed wrt each other there are two (different?) types of masses. The invariant mass and relativitic mass

M=m/sqrt(1-(v/c)^2), M=relativitic mass, m=invariant mass

How does the two masses in SR relate to the gravitational mass=inertial mass (lets assume they are equal for simplification)?

For one thing is it possible to measure gravitational mass=inertial mass in flat spacetime since acceleration of the masses must be needed but disallowed.

But from reading Wiki it seems that inertial mass = relativistic mass

http://en.wikipedia.org/wiki/Relativistic_mass

http://en.wikipedia.org/wiki/Mass_in_General_Relativity

http://en.wikipedia.org/wiki/Mass

However, in SR where all objects move with constant speed wrt each other there are two (different?) types of masses. The invariant mass and relativitic mass

M=m/sqrt(1-(v/c)^2), M=relativitic mass, m=invariant mass

How does the two masses in SR relate to the gravitational mass=inertial mass (lets assume they are equal for simplification)?

For one thing is it possible to measure gravitational mass=inertial mass in flat spacetime since acceleration of the masses must be needed but disallowed.

But from reading Wiki it seems that inertial mass = relativistic mass

http://en.wikipedia.org/wiki/Relativistic_mass

http://en.wikipedia.org/wiki/Mass_in_General_Relativity

http://en.wikipedia.org/wiki/Mass