Clever Apes: Uncanny slime

November 3, 2011

In the last installment of Clever Apes we visited a unique physics lab at the University of Chicago that studies the properties of granular materials. One area they’re investigating is the behavior of “oobleck,” which is nothing but cornstarch and water. The stuff is considered a “non-Newtonian fluid,” because it behaves as both a solid and a liquid. Dip your hand in it, and it acts like goopy liquid. Smack it, and it’s like a brick.

This little phenomenon, so simple that it could be demonstrated in most kitchens, is actually pretty poorly understood by science. The crew at the Jaeger physics lab is trying to get to the bottom of it – they whip up 20-gallon batches using a cement mixer. That made me happy. It also made me jealous. And so Clever Apes decided to do our own investigation, which we submit for your enjoyment.

I spoke with Scott Waitukaitis about the oobleck work – he’s a doctoral student at the lab who’s often elbow deep in this muck. He says it seems to be connected to the jamming effect that makes a vacuum packed bag of loose coffee grains hard as a brick. In this case, compressing the oobleck makes the individual cornstarch particles couple to one another. That means when you compress it quickly, you essentially make a big, if fleeting, solid object in your container of cornstarch goop. The size of the object is proportional to how hard you hit it.

It’s not clear why cornstarch is nearly unique in showing these properties (there are other materials that do it, but none so elegantly). Waitukaitis says it likely has to do with the particles being a particular size and weight in relation to water, and having no electric-charge interaction with one another. Whatever it is, makes a heck of a stiff solid when you sock it. He says some researchers are delving into applications for it, including a cornstarch (or custard) bullet-proof vest.

Meanwhile, the Jaeger lab is deep into the basic science of this uncanny slime. Waitukaitis shared the brief clip below of some of the fun they have. It’s taken on a high-speed camera.

There’s lots more fun with oobleck on the internet, including this trick with a speaker that we unsuccessfully tried to replicate. If any apes out there manage to do it, please share the secret with us.

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