5.3.3.8 Relativistic Mass
To derive the relation of the effective relativistic mass
, we can start from equation 5.6 above:
Now we can find
by differentiating
:
(5.17)
From this equation we find:
Replacing in equation 5.16 we get:
(5.19)
This method, however, can not be considered a mathematical validation of the mass-energy equivalence relation
, because the starting equation
is not derived by any other fundamental method from Relativity, other than being similar to the time dilation and length contraction:
,
.
Using the same equation
with
; thus:
, we can also derive the relativistic energy-momentum relation, by squaring and doing some modifications:
(5.20)
From this equation we get:
Thus:
(5.22)
Or:
(5.23)
Again, since this derivation relies originally on the equation:
, it can not be considered a mathematical validation of the mass-energy equivalence relation.


