Relativity always turns out to be more complicated than I think, but I believe it would be correct to say that E=mc

^{2} is for a mass at rest with respect to the observer. If the mass were moving at velocity v then the non-relativistic version of the equation might become:

**E = mc**^{2} + mv^{2}/2

But mass actually increases with relative velocity, so for a mass in motion I'm guessing that the equation might really be:

**E = mc**^{2} + mv^{2}/(2 * (1-v^{2}/c^{2})^{1/2})

But I'm just guessing. Modulous's answer in Message 151 may be the correct one, and his equation simplifies to:

**E = mc**^{2} / (1-v^{2}/c^{2})^{1/2}

Anyone know which is correct and why? I'm trying to see how Modulous's answer reduces to mv^{2}/2 (the Newtonian answer) for non-relativistic velocities after subtracting out an mc^{2}, but I can't figure it out.

--Percy