Julius Sumner Miller: Lesson 9 - Soap Bubbles and Soap Films

Soap Bubbles and Soap Films are not for child's play alone. Their study reveals some very important principles of Nature. Principal among these is this: That the Energy of a System tends toward Least. That is - the Energy of a System left to itself goes downhill. This is why raindrops are spherical; this is why a drop of water or a drop of mercury flattens out when it gets bigger. We show an array of exciting things:
A - THE DOUBLE BUBBLE PARADOX: We blow a small soap bubble and a big_ soap bubble simultaneously. Then we allow the two to be connected with each other. And a most remarkable thing happens! The SMALL one blows the BIG one bigger! We thus discover that the pressure in the smaller bubble is the greater. Which is NOT what most people think!
B - We fill a vessel very very full with water - so full in fact that it is
"humped up" high above the edge of the vessel. The surface behaves as a tight membrane - a stretched film - and is so strong in fact that we can float a steel needle on it!
C - We show some mercury droplets on a clean glass plate. When small they
are round; when bigger they flatten out. When two bubbles are brought very near to each other they coalesce - that is - they swiftly go together and become one. This action is incredibly swift and is most certainly electrical in nature.
D - We show an array of wire frames of various geometries dipped into a vat of soap solution. The soap films formed are very beautiful to see. When any one is punctured - broken - all the rest quickly take up a form such that the Energy of the System is again a minimum.
E - A circular frame has a loose string across a diameter. A soap film is formed covering the frame and the string. When the film is punctured at any spot the string instantly goes into a circular arc since a circular shape represents least Energy.
F - When a narrow small-bore tube - like a glass-tube - is dipped into water the water climbs INSIDE the tube higher than it is outside the tube. When this is done with mercury the mercury inside the tube is lower than the mercury level outside the tube. And the surface of the water is concave upward whereas the surface of the mercury is concave downward" We show this surface curvature with two wedge-shaped vessels.
Soap Films and Soap Bubbles and Drops are wonderful to play with and exciting to explore. Everyone - young and old - should read SOAP BUBBLES by C.V. Boys. Professor Boys describes hundreds of experiments which can be done at home or in school with utterly simple apparatus.