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
where:
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 }