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.
To show it we got Geraldine Chaplin to hammer in a nail into this liquid!
Why the stuff does this is a puzzle. The grains of cornstarch are so closely packed together that when the rod hits them, they have nowhere to go, like cars in a traffic jam. As with the traffic jam, untangling slowly is easy enough to do. But rushing things only cause you to rear-end or side-swipe the surrounding cars–or cornstarch grains. In both cases, this results in what is effectively a solid mass of material.