A bubble ring, or ring bubble, is an underwater ring vortex 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. Bubble rings and smoke rings are both examples of vortex rings, the physics of which is still under active study in fluid dynamics. Devices have been invented which generate bubble vortex rings. (video clip)