Cornflour slime

Science Concept

Stir thickening fluids become more viscous when pressure is applied.

Special instructions

Teachers should conduct their own risk assessment of this activity.

Gunkamena the Witch with a bowl of cornflour slime.

Class Time Required: 20 minutes

Materials

• Bowl
• Cornflour made from corn (ie not wheaten cornflour) – The amount will depend on how much slime you want. A 300 g packet of cornflour will make about two metric cups of slime.
• Food colouring
• Large spoon

What to do

1. Put the cornflour in the bowl and while stirring, add water a little at a time until all the cornflour is wet.
2. Add a few drops of food colouring to the mixture.
3. Keep adding water and stirring until a thick slime forms.
4. Make a fist and punch the surface of the slime - the slime will feel hard.
5. Do the same thing, but very slowly and your hand will emerge from the bowl covered in wet, sloppy slime.

What's happening?

Cornflour slime is a stir thickening (dilatant) fluid. Most fluids are 'Newtonian' and their viscosity (runniness) stays the same, whether or not they are being stirred. Cornflour slime is a non-Newtonian fluid. It becomes thicker (more viscous) when pressure, such as stirring, is applied. The slime returns to its runnier (less viscous) state when the force is removed.

When cornflour slime is punched, the cornflour particles lock together and the slime feels like a solid. When the slime is moved more slowly, the cornflour particles have time to roll over each other and the mixture flows like a fluid.