Weird Corn Starch trick
- Phaedrus May 29, 2008 07:45 PM
Can someone explain this?
No idea, but my guess is that a slight compression of the saturated starch granules pushes them into a lattice much like a polymer, allowing the solution to have extremely high surface tension supported by the sheer mass of the starch mud below.
At science fiction conventions, it's called "ooblek" (name taken from a Dr. Seuss book). As in
There's ooblek in the bathtub -- the con ain't over yet.
It's pleasantly disgusting, and it's thick and white and wet.
We know hotel security would say it's got to go,
So there's ooblek in the bathtub, but no-one's s'posed to know.
Google "ooblek" or "oobleck" and you'll find lots of explanations for how it works.
I think the reason cornstarch acts differently from flour is that it's virtually pure starch, while flour has gluten and other proteins.
"The most generally accepted explanation for the behavior of the cornstarch water mix is that when sitting still the granules of starch are surrounded by water. The surface tension of the water keeps it from completely flowing out of the spaces between the granules. The cushion of water provides quite a bit of lubrication and allows the granules to move freely. But, if the movement is abrupt, the water is squeezed out from between the granules and the friction between them increases rather dramatically." From http://www.seed.slb.com/en/scictr/not...
There's a little more on that site, and also here: http://kaffee.50webs.com/Science/labs...
Looking around, I find some disagreement about whether starch is a polymer. Hmph.
Never tried this with a bathtub full, but it was a standard "science for kids" experiment when I was young. It's somewhat related to Silly Putty (do they still make that?), which is soft when poked slowly but bounces like rubber when dropped.
My son did this at school in science a while back. He brought home a recipe for it but we haven't made it yet. I'm saving it for a rainy summer day when he's bored to tears.