Image courtesy of GoodNCrazy / flickr
Cornstarch and water have launched a thousand geeky pool parties. Stirred together in roughly equal proportions, they form a fluid that turns miraculously solid for a fraction of a second wherever it's struck. This means, as numerous YouTube clips attest, that you can run across the surface of a wading pool filled with the gooey mix without sinking. As long as you keep up your speed, stepping stones sprout out of the fluid and bear your weight.
Why the stuff does this is a puzzle. Scientists have usually studied it by pouring a teaspoonful on a metal plate, sliding another plate across the surface, and recording how the fluid pushes back. But that presents a problem: when you run across a pool of the fluid, after all, you don't slide on it, you stomp on it. Now the mystery--on which profound science admittedly does ...
