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2. Crash Bang! – Exciting experiments for you to try at home...
Slime, our old favourite, and a wow if you’ve never tried it before.
What you need
 Cornflour or custard powder (not instant custard)
Some water
A bowl
A spoon, or your hands
A cup for measuring
What you do
1. Mix 2 cups of cornflour with 1 cup of water, making sure to stir the water in slowly so you don't get any lumps.
2. The result is a strange white (or yellow if you are using custard powder) substance that will either act like a solid (if you punch it quickly or roll it into a ball) or it will act like liquid (if you touch it gently or tip the bowl).
3. If the mixture is not doing this you may need to add a little more cornflour or a little more water.
4. If you increase the amounts of cornflour and water, you could in theory fill a bathtub with the mixture, and run across the top without falling in. (You'd have to be very quick though!)
What's happening?
The cornflour and water mixture is a mixture of solid particles suspended in a liquid, called a “colloid". When you stir the mixture slowly, the custard powder particles can move around in the water quite freely, and so the mixture acts as a liquid. When you stir the mixture faster or hold it in your hand tightly, the solid particles rub against each other causing friction. This makes them stick together and the mixture will act like a solid. If you squeeze it really hard you will squeeze some of the water out and what remains will be more or less solid.
This activity came from the Slime activity on the SciCast site. |
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