Demos: 1Q-02 Non-Uniform Ang Accel


A chain with non-negligible mass is wrapped around a metal cylinder and passed over a pulley, where a small amount initially hangs vertically. The weight of the hanging portion creates a tension in the chain that, in turn, exerts a torque about the central axis of the disk. The torque uniformly increases as more of the chain passes over the pulley. Therefore the angular acceleration also increases uniformly, since the rotational inertia remains constant.

Directions: Allow a small part of the chain to hang over the pulley initially and make certain that the chain is securely wrapped around the cylinder. Then release the system.

Suggestions for Presentation: Discuss the origin of the torque on the cylinder. How does the hanging portion of the chain contribute to this? What happens if more chain is hanging? Does the rotational inertia change? Does the angular acceleration change?

Challenge: If you wanted the falling chain to move the disk at constant rotational speed, what compensations would have to be made?

Applications: None that are apparent.

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Last Updated: May 9, 2016 11:44 AM