Nearly everybody has, at some point, been fascinated by soap bubbles. A fun experiment is to dip a loop of wire into a soap solution and pull it out. As if by magic, a thin, transparent film of soap will form across the wire. Trying to predict what shape the soap film will be often yields a surprise. What makes the soap bubble take the shape of a perfect sphere, and what determines the shape of a soap film?

Soap Bubbles and Soap Films

Like many other physical systems, soap bubbles and soap films try to minimize energy. The energy in a soap bubble comes from the force of surface tension that holds it together and keeps it from popping. This energy is proportional to the area of the soap film.

Soap bubbles and films try to minimize their surface area.* A soap bubble...