Physics students often ask how it is that a massless photon can have momentum. In this video, Fermilab’s Dr. Don Lincoln shows that the question arises from a misuse of equations and also shows that, when you think about it, it’s not surprising at all. 

Why E = mc2 is wrong:
https://www.youtube.com/watch?v=eOCKNH0zaho 
 
The origins of mass:
https://www.youtube.com/watch?v=x8grN3zP8cg 

Further reading:
https://opentextbc.ca/universityphysicsv3openstax/chapter/relativistic-energy/

http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/releng.html

Fermilab physics 101:
https://www.fnal.gov/pub/science/particle-physics-101/index.html

Fermilab home page:
https://fnal.gov