This problem just came to my mind. I am wondering, what could be its solution. Here it is: Consider an isolated system. So there is no energy transfer from/to this system to/from outside. There is an observer with n identical balls with him in this system. Consider n>2. Initially these balls are at rest with relative to the observer. Now the observer applies some force to these balls. All these balls are spinning. Consider the conservation of angular momentum. These balls will spin in such a fashion, that their angular momentum is conserved. After some time, the observer holds one ball and stopped its spin. Will it change the spin of other (n-1) balls, so that their angular momentum is conserved?