"DW" == David Woolley <david@djwhome.demon.co.uk> writes:

DW> In article <40A26B94.4030001@somewhere.com>,
DW> "Rich <someone@somewhere.com>" <> wrote:

Energy has momentum, not mass.

DW> There seem to be different ways of interpreting relativistic mass,
DW> but E=mc^2 certainly gives a mass, and you have used the simple
DW> relativistic mass formula below, so you are not in the school of
DW> thought that says that there is no such thing as relativistic
DW> mass.

Oh, no, let's not go there.  The accepted definition for mass is that
it is an invariant quantity.  It is equal to the rest energy of an
object divided by c^2, so m = E_0/c^2, where E_0 is the energy
measured by an observer at rest w.r.t. to the object.

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