NOTES
Before I go further, I have to mention one of the most elegant theorems in mathematical physics - Emmy Noether's theorem that connects conservation laws with symmetries in the laws that drive the fundamental forces of nature. Here's a brief chart showing conserved quantities and the corresponding symmetries in the "action" (which is the difference between potential and kinetic energy, integrated over time for a particular path through space-time).
There are some real-world systems for which this theorem does not apply, but I'm not going to get into that today.