Let me stop "lurking" long enough to suggest that those interested
read my article, "In Defense of Relativistic Mass" in the November 1991
issue of the American Journal of Physics, pages 1032-36. I apologize for
the quality of its writing, but both the editor and the reviewers were
anti-relativistic mass and the agony of getting something that they'd
agree to publish resulted in a paper that reads like it was written by a
committee.
The controversy over relativistic mass has reminded many of
arguments over religion--but unless you truly believe there is only one
way (your way), you will agree relativistic mass can be used or not.
However, with relativistic mass, the equation E = mc^2 beautifully
unifies the previously disparate concepts of mass and energy--energy and
mass are equivalent and c^2 is merely the conversion factor from mass
units to energy units. Isn't this one one the great unifications of modern
physics?
Without relativistic mass, energy and mass are sometimes
equivalent, sometimes not. Read the article for examples and for
discussions of other topics that have been mentioned such as "converting
mass to energy" and mass as an additive quantity.
Tom Sandin