Smoke ring

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.

A smoker may create rings by taking smoke into his mouth and expelling it with a tongue flick, by closing the jaw, tapping the cheek, or producing a sudden burst of air with the lungs and throat. The smoker may also use any of those methods to blow into a cloud of smoke outside his mouth.

A trick often performed in conjunction with mouth-blown smoke rings is the .

It is also possible to create a vapour ring by using the same techniques on a cold day with only one's breath.

The most famous such steam rings were those produced during the mid-20th century by Douglas Leigh's billboard on the Hotel Claridge in New York City's Times Square, advertising Camel cigarettes. An automated steam chamber behind the billboard produced puffs of steam every four seconds, giving the appearance of smoke rings leaving the smoker's open mouth and drifting away. Inspired by a World War II-era prohibition on lighted advertising, the Camel smoker remained a Times Square landmark long afterward.

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