Rectifier wrote:
Photons (the particle nature explanation of EMR) have no mass:
http://www.physchem.co.za/OB12-ele/radiation.htm

They should have said "no rest mass" to keep the
uninitiated from getting confused. Any particle that
can apply pressure, possesses momentum and "penetrating
ability" at the least has relativistic mass.

http://math.ucr.edu/home/baez/physic...oton_mass.html

"In special relativity, it turns out that we are still able to
define a particle's momentum p such that it behaves in well-
defined ways that are an extension of the Newtonian case.
Although p and v still point in the same direction, it turns
out that they are no longer proportional; the best we can
do is relate them via the particle's 'relativistic mass'."

"It is almost certainly impossible to do any experiment that
would establish the photon rest mass to be exactly zero."
--
73, Cecil http://www.w5dxp.com