E    Mass, Momentum and Energy

We now turn from kinematics to dynamics.  In the first section we examine in the context of an elegant thought experiment, what influence a relative motion has on ‘mass’ and ‘momentum’. This provides a new argument for the fact that c is a limiting velocity. We also introduce a beautiful Epstein diagram for mass and momentum, which corresponds to the one for space and time. We then turn to the meaning of energy and recognize that energy must have inertial mass. But how much mass does a given quantity of energy have? A calculation provides the best known formula of all of physics.
This result can also be presented in an Epstein diagram for energy and momentum.