We all know classical mechanics deal with bigger objects and quantum mechanics deal with very tiny particles.
I hear spin number in quantum mechanics, but I don't see anything like that in classic mechanics.
Why don't we calculate spin number in classical mechanics?
Loosely speaking: Classical mechanics is the approximation of quantum mechanics in the limit of $\hbar \to 0$ (where $\hbar$ is Planck's constant).
In quantum mechanics the electron's spin is given by $$\vec{S}=\frac{1}{2}\hbar\vec{\sigma}.$$ where $\sigma_x$, $\sigma_y$, $\sigma_z$ are the Pauli matrices.
The classical limit (for $\hbar \to 0$) of this is obviously:
$\vec{S}=\vec{0}$.
That means: There is no spin in classical mechanics.
Spin is an entirely quantum mechanical phenomenon.
