This demonstrates trajectories of three interacting vortices confined within a circle. Vortices are an interesting mechanical system. As opposed to masses or solid bodies, their evolution is described by first-order differential equations in time. Using mirror vortices, it is possible to restrict the motion of the vortices within a disk. G.-C. Yuan, K. Nam., T. M. Antonsen, E. Ott, P. N. Guzdar. Chaos 10, 39 (2000).