More on Bubbles

{ image borrowed from: dive/Siau.html }

The reader is also no doubt familiar with blowing bubbles underwater, that is, bubbles of a gaseous

nature surrounded by some fluid of a considerably higher density. Such bubbles tend to rise to the

surface (due to the buyant force), during which time the surrounding pressure lessens allowing the

bubble to expand in order for inner and outer pressures to remain essentially equal. Some of you

have probably, while watching a bubble on its ascent, noticed the strange side to side oscillatory

motion the bubble makes on it's journey upward. Leonardo Da Vinci was among the first to attempt a

description of this peculiar motion {4}. Such a description of this spiraling motion {5}is beyond the

scope of this site, but the reader might be interested to note that each time a bubble suddenly moves

one way it has shed a vortice which moves in the opposing direction so that after many such motions

the bubble leaves behind it a vortex street (see figure below).

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NOTE: While not the result of a bubble, the interesting satellite picture above is a good example of a vortex

street (this particular one results from wind blowing around an island somewhere off the coast of Greenland){6}.

These bubbles that we are talking about can form not only by injection of a gas into a liquid but also

spontaneously themselves out of a liquid. This occurs when the temperature of a liquid under

constant pressure raises above that liquid's boiling point. These bubbles are familiar to all as those

that form in boiling water (they can also form when the pressure surrounding a liquid at constant

temperature is reduced). Under these circumstances the bubble is made up of vapor of the medium it

is immersed within, this is because the vapor pressure of the fluid has surpassed that of the outer

atmosphere (the pressure exerted upon the fluid) and so allows the fluid vapor to escape at much

faster rates than are otherwise allowed (such as normal evaporation){7}.

{ image borrowed from: photogallery.html }


Bubble Resonance