Capillarity and Wetting Phenomena - de Gennes, Pierre-Gilles a Brochard-Wyart, Francoise a Quere, David

As I rush into my car under a pelting rain, my attention is caught by small drops stuck on my windshield. I also notice larger drops rolling down and others larger still that, like snails, leave behind them a trail of water. I ask myself what the difference is between these rolling drops and grains of sand tumbling down an incline.