# Lorentz invariants

QuArK21343
Why is it that charge is Lorentz invariant (it's a scalar, independent of the frame of reference) whereas mass is not? Does this mean that the gravitational force a body exerts depends on the frame of reference, whereas the electric force doesn't?

The mass of a particle is also a Lorentz invariant. You may be thinking of the relativistic mass γm.

QuArK21343
Ok, since this is new to me, could you clarify the difference between the two? Do you mean the rest mass is Lorentz invariant? Anyway, there is no analogue to relativistic mass as far as charge is concerned (no relativistic charge), right?