A Rod Sliding in a Semicircular Well

This Demonstration shows how a rod of length moves sliding down the side of a semicircular well of radius . At the beginning one end of the rod is held at the edge of the well with the other in contact with the side of the well. Once the system is released, the rod slides down the well under the influence of gravity. Assume there is no friction acting between the points of contact of the rod and the well.