The relation between gravitational mass, inertial mass and velocity, Ling Tsai, Am. J. Phys. 54(4), April 1986
This work concerns a "thought experiment" using a balance whose arm length can be varied in the order to prove that, within the scope of special theory of relativity, both inertial mass and gravitational mass of a moving body obey the relationship m = m0/sqrt(1 - b2). Therefore, if the inertial mass of a body and its gravitational mass are strictly equal, then they are still equal when the body moves high velocity. The argument extends Einstein's principle of equivalence to special relativity.