Angular Momentum: Feynman's Physics Explained
In quantum mechanics angular momentum is quantized: its component along any axis can only take a discrete ladder of values separated by whole units. Stranger still, the different components do not commute — know the value along one axis exactly and the other two become uncertain. This non-commuting is the mathematical root of spin and of the quantization of angular momentum itself.
The big idea
Even spinning is quantized — angular momentum comes in discrete steps.
Think about it
Why can you never simultaneously know a quantum object's spin along all three directions at once?
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