Gloopy oobleck

Is it a liquid or a solid?


Take a look at this video to see the impressive effects of oobleck:

Oobleck is made of ingredients you probably have in your home already!  Cornstarch or cornflour is often used to thicken sauces, among other things, but when you mix it with water something amazing happens.  It becomes a non-Newtonian fluid.  It is a kind of smart material. When you hit hard it behaves like a solid. But if you push it slowly it behaves like a liquid. This is because of the viscosity of the liquid; viscosity is how well a liquid flows or how resistant it is.

What's going on?

Cornflour is made up of lots of tiny (<0.01mm) starch particles. These are very attracted to water, so the water gets in amongst them very quickly.

The water acts as a lubricant, so when you move the cornflour slowly, the particles have time to move past each other and they can flow like a liquid.

However, if you apply a rapid force it causes the particles to move slightly. The particles that are almost touching  jam together and the water that was between them moves sideways slightly into the gaps. Now instead of having lots of lubricated individual particles you have a solid structure of lumps touching each other which can't flow.

Cool stuff isn't it?  Take a look at this next experiment to see how even sound pressure has an effect.  Don't try this one at home without out permission from the parents and a lot of newspaper!

Making your oobleck dance:

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