Why is Quantum Spin measured in JouleSeconds?

Question

To my knowledge, the unit of quantum spin is h-bar on two.

This has units of Joules times seconds divided by radians.

The radians part makes sense to me, the Joules Seconds part, does not.

Why is it not measured in Newton Seconds like regular momentum?

(If anyone knows how to use the math code on this website, I'd appreciate an edit of the second line to make things a tad clearer.)

Answer 1

Spin is an angular momentum, so it has dimensions of moment of inertia times angular velocity i.e.

$$ [\text{Spin}] = [ML^2][T^{-1}] = [ML^2T^{-2}] [T] = [\text{Energy}][\text{Time}] $$