M-ST 4: Soap films

PIRA: Unknown

Equipment: wire frames and soap solution located in Set 11, Cabinet 1, Shelf 4.

Procedure: There is on the equipment shelves a set of wire frames designed to make soap films which are plane surfaces intersecting at a point along a line, and curved surfaces. Because the surface tension has the same value for every element of the surface, these soap films have some interesting geometric properties which are best learned by consulting standard works on the subject.

One frame consists of a wire loop to which is attached a loop of thread. If this is dipped in soap solution a plane film is formed with the thread imbedded in the film. If then that portion of the film inside the thread loop is destroyed by touching with a hot wire, the thread loop opens out into a circle.

A curved film open to the atmosphere on both sides must be saddle-shaped with equal positive and negative curvature at each element. To obtain curved open films it is best to start with a complicated three-dimensional set of plane intersecting films (such as can be formed on a wire cube) and destroy one or more films by the hot wire technique.