Why do puddles stop spreading?
When you spill a bit of water onto a tabletop, the puddle spreads — and then stops, leaving a well-defined area of water with a sharp boundary. There’s just one problem: The formulas scientists use to describe such a fluid flow say that the water should just keep spreading endlessly. Everyone knows that’s not the case — but why? This mystery has now been solved by researchers at MIT — and while this phenomenon might seem trivial, the finding’s ramifications could be significant: Understanding such flowing fluids is essential for processes from the lubrication of gears and machinery to the potential sequestration of carbon dioxide emissions in porous underground formations. The new findings are reported in the journal Physical Review Letters in a paper by Ruben Juanes, an associate professor of civil and environmental engineering, graduate student Amir Pahlavan, research associate Luis Cueto-Felgueroso, and mechanical engineering professor Gareth McKinley. “The classic thin-film model describes...