Two ideas of momentum:  Mechanical and canonical.

Conservation of momentum and energy in field theory.

Interaction of fields and particles, mechanical momentum vs. canonical momentum.

Invariance under a phase transformation implies conserved electric charge.

1. Inertial Reference Frames
2. Principle of Least Action
3. Invariance of the Laws of Nature
4. Lagrangian Mechanics
5. Conservation of Charge and Momentum
6. Relativistic Wave Equation and Conservation Laws
7. Invariance under Gauge Transformations
8. Gauge Theory

This Stanford Continuing Studies course is the second of a six-quarter sequence of classes exploring the essential theoretical foundations of modern physics. The topics covered in this course focus on quantum mechanics. The course is taught by Leonard Susskind, the Felix Bloch Professor of Physics at Stanford University.