[AtomicX (OP)]

If a photon moves with the speed of light it has kinetic energy, right? Then why does its energy only relate to the frequency and momentum of it? E=pc & E=hf. Please could someone explain?

[guest45734]

If a photon moves with the speed of light it has kinetic energy, right? Then why does its energy only relate to the frequency and momentum of it? E=pc & E=hf. Please could someone explain?

Because photons do not have mass.
Photons gain or lose energy due to gravity or by colliding with atoms etc.

Edit

This attachment was posted by Peter on another thread ref different definitions of mass.