1. The problem statement, all variables and given/known data A uniform rod of mass M and length L rotates in horizontal plane about a fixed axis through its center and perpendicular to the rod. Two small rings, each with mass m are mounted so that they can slide along the rod. Rod rotates with the initial angular speed of ω. 2. Relevant equations What is the angular speed of the rod after the rings leave it? 3. The attempt at a solution The answer books says, that it is the same angular speed as the rings would have slided to the both ends of the rod and stuck there. Now knowing this it would be a simple use of conservation of angular momentum. However I do not understand why the rod rotates with the same angular speed in both of these cases: 1. The little rings slided to the ends of the rod. 2. The little rings slided out completely out of rod. The moments of inertia at both cases are different, so how come they have the same angular speed?