Disk (weighted off-center) rolls up inclined plane.

The Weighted Disk (also called Feeble-Minded Disk.) Stable, Unstable, and Neutral Equilibrium. The wood disk has a lead weight placed off-center, near the rim. (The weight is painted black on one side of the disk, but is not shown on the other side of the disk). The instructor positions the disk at the bottom of the ramp, with the weight at the top and hidden from view. The disk is then allowed to roll up the plane, and the students are asked how this can happen.