What Are Bubbles?

{ image borrowed from: www.rci.rutgers.edu/ ~jhudson/331.html }

Most everyone has, as a child, wondered with amazement at these seemingly magical creations,

bubbles, but what exactly are they and how do they form? It turns out that for the ordinary types of

bubbles we evidence everyday such as the soap bubble, one of the most important properties

governing it's structure is the surface tension of the fluid involved. the expression relating the size of

a bubble to surface tension is called Laplace's equation {2}(one of MANY equations so labeled) and

has the following form (assuming a spherical bubble):

T = PR/2


T = surface tension

P = internal pressure

R = radius of bubble

Consider as an analogy {2} that we have a cable held horizontally supporting some weight. We see

that with less tension in the cable the system tends to sag more. We have also though that the inward

component of the tension must equal the outward pressure of the bubble, hence as the bubble grows

in radius and curvature consequently is decreased the total tension must increase in order for the

inward component of tension to remain the same (see figure below, but note that the decrease in

internal pressure that one would expect to accompany expansion is not taken into account).

{image borrowed from: http://hyperphysics.phy-astr.gsu.edu/hbase/ptens.html#bal }

We can gather from this then that a fluid having some low surface tension will not be able to support

as large a bubble as a fluid posessing a higher surface tension. Such is the case with ordinary water,

for normally one cannot create and sustain bubbles of any significant size, yet when a surfactant

(some compound that raises the surface tension of a fluid) is introduced we may evidence firsthand

that bubbles will readily form (as is exemplified when one adds soap to water yeilding a fluid

possessing higher surface tension). There are however many more types of bubbles than the

commonly encountered soap bubble.

{ image borrowed from: www.zurqui.co.cr/crinfocus/ bubble/bubble.html }


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