Science Experiments

Cornflour and Gravy

Sun, 26th Feb 2006

Part of the show The Science of Nanotechnology

What you Need

A saucepan

A stove

A wooden spoon

Water ~ 250ml

Some Cornflour (Cornstarch) ~ a few teaspoons

What to do

Put the water in the Saucepan

Add a couple of teaspoons of cornflour to the water

Heat the water until it is simmering

THIS SHOULD BE DONE WITH AN ADULT

Keep stirring until something happens

Add some cornflour to the hot water, how does this behave?

 

What may happen

When the mixture gets hot and you stir it, it will get thicker and thicker

If you add the cornflour to the hot water it will turn into a lump covered in a jelly like substance.

We also heated some cornflour particles under a microscope with a hot air blower, which allows you to see what is going on.

Expanding Cornflour Particles 1

Expanding cornflour particles 2

The particles start off small and compact surrounded by cold water.

The water can be heated considerably with not much effect on the particles,

Expanding Cornflour Particles 3

Expanded cornflour particles

Over a critical temperature the particles start to swell up .

They keep swelling until they almost dissolve and start to become difficult to see.

Here is the same process as a video.

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