NEW YORK (Dispatches) -- Researchers have described a simple model that captures the key mechanics of hand-washing, the American Institute of Physics reports.
They estimated the time scales on which particles, like viruses and bacteria were removed from hands, by simulating hand-washing.
The mathematical model acts in two dimensions, with one wavy surface moving past another wavy surface, and a thin film of liquid between the two. Wavy surfaces represent hands because they are rough on small spatial scales.
Particles are trapped on the rough surfaces of the hand in potential wells. In other words, they are at the bottom of a valley, and in order for them to escape, the energy from the water flow must be high enough to get them up and out of the valley.
The strength of the flowing liquid depends on the speed of the moving hands. A stronger flow removes particles more easily.
Study author Paul Hammond likens the process to scrubbing a stain on a shirt: the faster the motion, the more likely it is to come out.
Results from Hammond’s model agree. It takes about 20 seconds of vigorous movement to dislodge potential viruses and bacteria.