Experiment 1 - Walking on custard

Thanks to TV show Brainiac we can get a very dramatic demonstration of how custard changes state under pressure.

We usually think of materials changing state as a result of variations in temperature. Cool down water and it becomes ice. Heat up a piece of metal and it becomes molten metal. But pressure can also have a dramatic effect on some materials. Thixotropic non-drip paints change between gel form (a gel is a very malleable solid) and liquid when stirred. But the most dramatic and fun demonstration of the effect of pressure on state of matter is provided by custard.

Click the image to watch the video.
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Experiment 1 - Walking on custard

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Mix custard powder with water so you get a thick yellow liquid. Pour some into a bowl. Now put your finger and thumb into the liquid a few centimetres apart and squeeze them together. The liquid becomes a dry powder under the pressure of your fingers. As long as you keep the pressure up, it will stay solid - you can easily lift it out of the bowl - but as soon as you relax the pressure it will return to liquid and drip from your fingers.

If you don’t have any custard to hand, or want to see this effect more dramatically, take a look at the video.
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