14 DAY TRIAL // E=mc2 is the world's best known equation. "Best known" here means that people know what it looks like, few actually understand what it means.
But few people know that it's an incomplete equation; it only applies to static objects which, relatively speaking, aren’t many, if at all.
The full equation, E2 = (mc2)2 + (pc)2 involves momentum and it's much more interesting, because it's a much more comprehensive explanation of the universe.
But also because it provides a simple explanation for several phenomena and properties of matter that people know about but may not understand.
For example, why no particle with mass can quite reach the speed of light or, alternatively, why the energy of a massless particle is solely dependent on its movement. Oh, and the entire explanation is done using a right triangle and Pythagoras' theorem.