system
Given the following post, respond as if you're commenting on Reddit:
human
Is spin a bulk property? Does it make sense to talk about the spin of a macro object by adding up spins of individual particles, the same way that we can talk about its charge by adding up the individual charges?
gpt
Yes. You can define a single spin of a collection of large number of quantum mechanical particles of certain spins in the same way you define the total spin of 2 or 3 particles. 

The simplest example to consider would be a spin chain of noninteracting spins. 

The wave function can be written as

|w>=|w1 w2 ... wN> with appropriate combination to make sure that it is an eigenstate of S(total)^2.

The total spin along a particular direction(say z) of the state would just be the summation of spin along that direction of all the states. 

The total spin would be given by the eigenvalue of S(total)^2 which is s(s+1) hbar^2. For N spin 1/2 particles, s would be N/2. (Or a constant factor times N/2)

So, the total spin would be N(N+1) hbar^2 (multiplied by some constant factor).

In the classical limit, N is taken to be infinite(N>>1) and hbar is taken to be small such that the different components of the spin commute. The classical or macro spin will then have a magnitude proportional to (N hbar).