How can photons have momentum if they have zero mass?

Question

I understand E = hv, but I’m not getting why photon collisions can “push” things instead of just producing heat. Thanks!

In: Physics

Answer 1

E=mc^2 is only 1/2 the equation.

its actually E^2 = (mc^2)^2+(pc)^2

E=mc^2 is for rest mass.

E^2 = (mc^2)^2+(pc)^2 is for something in motion.

If it has no mass, mc^2 term drops out then you have E=pc for a massless object. The pc term only become relevant when the velocity of the massless thing is very high (near c), otherwise the mass term is orders of magnitude larger and dominates the equation.