What is the relationship between quantum spin and classical spin? I have seen this question asked many times but have never seen an answer that I was happy with. The most common answer I have seen is that there is no connection. The word "spin" has more to do with history than physics and there is no more connection here than there is between color forces between quarks and the color red. But then others have pointed out that spin, either quantum or classical is angular momentum. Can you convert classical spin to quantum spin? For example what would happen if you fed a black hole some polarized light? Can an object have both quantum spin and classical spin? Can a proton have classical spin for example? How about a proton attached to a neutron? A methane atom? A large protein? A baseball? Is classical spin quantized? It would seem that it must be but then you have two different kinds of quantum spin. . .