- A ring of smoke exhaled by a smoker.
2013 March 1, Frank Fish, George Lauder, “Not Just Going with the Flow”, in American Scientist, volume 101, number 2, page 114:
- An extreme version of vorticity is a vortex. The vortex is a spinning, cyclonic mass of fluid, which can be observed in the rotation of water going down a drain, as well as in smoke rings, tornados and hurricanes.
- A smoke ring persists for a surprisingly long time, illustrating the slow rate at which viscosity dissipates the energy of a vortex.