A single bead can slide with negligible friction on a stiff wire that has been bent into a circular loop of radius 12.4 cm, as in the figure below.

A single bead can slide with negligible friction on a stiff wire that has been bent into a circular loop of radius 12.4 cm, as in the figure below. The circle is always in a vertical plane and rotates steadily about its vertical diameter with a period of 0.445 s. The position of the bead is described by the angle that the radial line, from the center of the loop to the bead, makes with the vertical.