Well, you see, we are both right...
There is rest mass[/color] and relativistic mass[/color].
it is described very good
here.
In this context, the quantity m is sometimes called the relativistic mass.
Well, i believe one should understand "sometimes"[/color], in the quote above, as a result of that this quantity is convinient in a very small area of physics.
I'try to explain why:
Consider the expression for the energy:
E=m[/color]*c^2/sqrt(1-v^2/c^2);
here m[/color] - is a rest mass.
You can surely rewrite this as
E=m[/color]*c^2;
with m[/color] denoting the relativistic mass.
But the problem (well not a real problem) arises when you try to derive the expression for the force from the momentum (p=E*v/c^2)...
Using the relativistic mass, the momentum is written as p=m[/color]*v - as in classical physics.
Deriving it, we receive the expression for the force, where
relativistic gamma is in the power of 3/2 (if considering rest mass), and if we try to substitute a relativistic mass, we will not[/color] receive F=m[/color]*a...
Not very convinient? eh?
Moreover, it is difficult to give the relativistic mass a real physical interpretation. That's why in modern physics rest mass is preserved, and it is much more convinient to use
E=m[/color]*c^2*(relativistic gamma)[/color]
p=m[/color]*v*(relativistic gamma)[/color]
and so on...
But of course, i agree with you, if dealing with relativistic mass -
it is being increased...
That's what i meant :)