Soap film flows
1,743 views · Published 11 August 2011 · 0:54 · Indexed 11 October 2026
Channel: Paul Nathan · 2011 · Education
A nice demonstration of soap film flows from an entrance display case at MIT. These are almost perfect two-dimensional flows that are rotational and viscous. Chaotic mixing and highly non-linear vortical motions can arise, but nonetheless the flow is never turbulent because there is no vortex stretching dissipative mechanism since all vortices have their axes aligned perpendicular to the plane of the interface. The soap film has thickness on the order of the wavelength of light at visible frequencies such that it acts as an interferometer. Each colour band corresponds to a thickness that is some integer multiple of the wavelength of the particular colour (frequency) of light. Since the scene was illuminated with broadband white light, the full spectrum can be observed. So blue regions are thinnest and red regions thickest. All motions are thus driven by gravity / buoyancy forces. Now I have a new side project to make one of these :-D. I did begin to make one back in 2008, but never quite completed it.... this time things will be different!
