Why Does E=mc²? Brian knows & he's wicked good at explaining things!
I am going to keep recommending AWESOME books about physics until I get my act together on continuing work on this website - The History of Physics Timeline in particular (instead of arguing with trumpers 100% of the time).
Ever wanted to read a lucid and sublime journey through the most famous equation ever? Professor Brian Cox has a book for that and it rocks.
Check it out! Why Does E=mc²? by Professor Brian Cox and Professor Jeff Forshaw. Feet off the table and gum in the trash. Class is in session!