Quantum Spin Class

Regular spin of a spherical mass; angular momentum; spin axis.
Analogy with quantum spin:
  What are the similarities?
  What are the differences?

Math is similar: quantum spin acts like angular momentum.
But it's quantized in units of h.
Spin axis:  Lz vs. Lx and Ly
Measurements along orthogonal axes:
  Regular spin: Lx and Ly = 0
  Quantum spin: value is +/- 1/2 but probabilities are independent.
  Measuring Lz along the true spin axis always gives the same value.


We don't have to call the quantum version "spin": we could call it "schmaltz".
But the analogy is compelling, so "spin" is more helpful than misleading.

Measuring spin of a sphere: select an axis z, draw a plane normal to the axis that
cuts through the center of the sphere.  Place a dot on the sphere's equator and trace its
and trace its circular path on the plane. The speed of rotation times the mass gives
the angular momentum (times the radius) gives the angular momentum, or spin.