Some of the science books I have read use the concept of relativistic mass and some don’t. All of the books that do use this concept define as it as m[sub]0[/sub]*gamma, where m[sub]0[/sub] = the rest mass and gamma = 1/(1–v[sup]2[/sup]/c[sup]2[/sup])[sup]1/2[/sup]

However I have since learned that there are actually two relativistic masses, the longitudinal relativistic mass and the transverse relativistic mass. Where m[sub]RL[/sub] = gamma[sup]3[/sup]*m[sub]0[/sub] and m[sub]RT[/sub] = gamma*m[sub]0[/sub].

What’s going on here?