gooey particle experiment

Playing with Cornflour Goo is a fun way of seeing how particles in a substance can behave in very different ways.

What you’ll need

  • Cornflour, as much as you can
  • Water
  • A bowl

What to do

Put most of the cornflour in the bowl

Add water to the cornflour until it starts behaving strangely - you will want at least twice as much cornflour as water, so don't add it too fast.

Try moving your hand through the liquid slowly, then fast, have a play with it.

What may happen

You end up with a really strange mixture; when you move slowly it will flow slowly, but if you try and change its shape quickly it goes hard. If you get the consistency right, you can even roll a ball out of it that will bounce, then when it stops, flows as a liquid again. It is known as a shear thickening liquid.

Why does it happen?

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 it 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 causing the particles that are almost touching to jam together, and the water that was between them moves sideways slightly into the gaps.