Scientists at the University of Chicago have been focusing a high-speed camera on dripping glycerine in the hope of catching the moment when the fluid drop breaks off. By taking 10,000 frames per second of a glycerine and water mixture dripping through a nozzle, they have captured images, such as the one shown here, of a drop at the point of snap-off.

According to an analysis of these images published in Physical Review Letters (83, 1147-1150; 1999), drops about to break free are self-similar — that is, the shape of the drop just before breaking looks the same at different times, if you rescale the axes. Understanding such fractal behaviour is important for the physics of mixing, because the quality of a dispersion — crucial when spray-painting cars, for example — depends on the way it breaks into drops.

Getting to grips with the mathematics of this problem may be relevant to other areas of physics, such as theoretical studies into the gravity around black holes. When a fluid drop is about to break, a singularity develops, rather like the space- time singularity of a black hole. Simulating the infinite character of gravitational collapse remains a mathematical headache, and so studying a dripping tap may be an attractive alternative.