 # Relativistic mass

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] = gammam[sub]0[/sub].

What’s going on here?

Well, this is news to me. And “longitudinal relativistic mass” returned zero hits on Google. Where did you hear it?

Check section 1.4 about half way down the page. Finkelstein is the guy who developed the Finkelstein Reference Frame, and he’s pretty famous.

It’s also in “Introduction to Special Relativity” pg 93 by Wolfgang Rindler.

Plus I got 57,000 hits on Google when I searched on mass, transverse, longitudinal.

Ok, I got it. If you define force as dp/dt instead of m*a and demand that momentum be conserved then the need for longitudinal mass disappears.

The original requirement for longitudinal/transverse mass was due to having both length contraction and time dilation in the direction of motion, but only time dilation perpendicular to the motion.

Damn, I did it again. The above post was by me not Ring. Please don’t tell him.