A bubble ring, or toroidal bubble, is an underwater vortex ring where an air bubble occupies the core of the vortex, forming a ring shape. The ring of air as well as the nearby water spins poloidally as it travels through the water, much like a flexible bracelet might spin when it is rolled on to a person's arm. The faster the bubble ring spins, the more stable it becomes.[1] Bubble rings and smoke rings are both examples of vortex rings—the physics of which is still under active study in fluid dynamics.[2][3] Devices have been invented which generate bubble vortex rings.[4][5]