Why do puddles stop spreading?

8 julio 2015

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 — and while this phenomenon might seem trivial, the finding’s ramifications could be significant.