(Lecture: 20 minutes)

See the second half of §9.3 of the text.

Having set the stage in the previous lecture for Newtonian conservation laws, it is straightforward to repeat the derivation in the relativistic case. However, the Einstein addition law leads to quite different conclusions — and the derivation becomes an exercise in the addition formulas for the hyperbolic trig functions.

It is worth going over both this lecture and the preceding one in advance in order to ensure a smooth presentation — the instructor should make sure to decide which way the reference frames are moving, and what notation to use for the quantities in each reference frame.