Oobleck

No, not the Dr. Seuss stuff – though that’s how this mixture of cornstarch and water got its name.

I have a habit of dropping in on the Discovery:Science channel (in spite of the fact that it’s tucked in the most obscure section of the cable channel spectrum). The other day, I found a couple of geeks talking about walking on water. They mixed cornstarch and water in a cement truck (do they rent cement trucks out for things like that?) and poured it in a large vat, then walked right across it. As long as they moved quickly, slapping the surface of the oobleck with their feet at each step, they could walk on it. And when they rolled a ball of oobleck between their palms, it was solid; as soon as they stopped rolling, it became a liquid and poured right through their fingers.

How cool is this? Check out more at the Science Café, where they explain it a lot better than I do. And they include video of the whole walking on water thing. And for more coolness, if you put a bowl of the stuff on a bass woofer, the vibration will make it grow and dance (which is what it’s doing in the picture above; the green is just food coloring).

It seems oobleck is a non-Newtonian fluid, meaning it changes in viscosity depending on how much pressure is applied to it. Turns out, it’s the same as quicksand. When I was a kid, quicksand was explained to us as sucking you down if you struggled, and the trick was to move slowly. Now I’ve learned that’s because it’s a non-Newtonian fluid. Boy, does that sound smarter than “it sucks you down.”

Ketchup is the opposite kind of non-Newtonian fluid: when agitated, it becomes less viscous, which is why we all shake the ketchup bottle. To me, that’s what happens to any relatively thick liquid sitting in a bottle. But what do I know? Maybe they’re all non-Newtonian fluids.

The really interesting thing I’ve learned through all this is that those under about 20 years of age, and parents with kids under that age, know all about this. Teachers have been doing oobleck demonstrations in grade school for decades. Hey, I feel cheated – we never got to do stuff like this. Can I go back to elementary school and catch up on the fun stuff?

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