Photon, Momentum, Mass

Ok first I'd like to say thank-you to those who responded to my last
post. I kind of get whats going on now with the different frames of
reference.

But what still has me confused is this idea that a photon can be
regarded at times to have a 'relativistic mass', while also having no-
mass at other times. What I mean is this, does a photon change its
behavior from a particle of mass to a particle of no-mass ?

How was it determined that light exerts pressure on objects ?

and,

If light has this 'relativistic mass' is it a constant value, or does
it change ?

I have read that if light is contained within a box with perfect
mirrors then it is considered that light adds mass to the box, and
that there is energy but no momentum within the box's frame of
reference. This is in contrast to freely moving moving particles.

So, what happens when light is moving freely, then it gets trapped
into the box then escapes the box.

Does this mean the photons of that light go from having no-mass to
having mass within the box, to having no-mass again when its outside
the box ?

I mean to me, that sounds ridiculous.

-y

.

Relevant Pages

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