A smoke ring is a visible vortex ring formed by smoke in a clear atmosphere.
Smokers may blow smoke rings from the mouth, intentionally or accidentally. Smoke rings may also be formed by sudden bursts of fire (such as lighting and immediately putting out a cigarette lighter), by shaking a smoke source (such as an incense stick) up and down, by firing certain types of artillery, or by the use of special devices, such as vortex ring toys. The head of a mushroom cloud is a large smoke ring.
A smoke ring is commonly formed when a puff of smoke is suddenly injected into clear air, especially through a narrow opening. The outer parts of the puff are slowed down by the still air (or by edges of the opening) relative to the central part, imparting it the characteristic poloidal flow pattern.
The smoke makes the ring visible, but does not significantly affect the flow. The same phenomenon occurs with any fluid, creating vortex rings which are invisible but otherwise entirely similar to smoke rings.
When blown in still air, a smoke ring usually travels roughly straight from the opening over a surprisingly large distance, maintaining its shape, until dispersed by turbulence or other interference.
Read more about Smoke Ring: Smoking and Breathing, Volcanoes
Famous quotes containing the words smoke and/or ring:
“Forty years after a battle it is easy for a noncombatant to reason about how it ought to have been fought. It is another thing personally and under fire to have to direct the fighting while involved in the obscuring smoke of it.”
—Herman Melville (1819–1891)
“Time has no divisions to mark its passage, there is never a thunderstorm or blare of trumpets to announce the beginning of a new month or year. Even when a new century begins it is only we mortals who ring bells and fire off pistols.”
—Thomas Mann (1875–1955)