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Stressed? This slime is better than any stress ball. It will force you to be slow and gentle while teaching you the virtue of patience. If you get angry and decide to punch it, it will always get the better of you.
What you need
- cornflour made from corn (ie not wheaten cornflour)
- water (the amount of water required will depend on the amount of cornflour used)
- large spoon
- food colouring
Note: The amount of cornflour required will depend on how much slime you want to make. A 300 gram packet of cornflour will make about two metric cups of slime.
What to do
- Place the cornflour in the bowl.
- Use the large spoon to stir the cornflour while adding the water a little at a time. Keep stirring and adding small amounts of water until all the cornflour is wet.
- Add a few drops of food colouring to the mixture.
- Keep adding small amounts of water and stirring until a thick slime forms.
- Make a fist and punch the surface of the slime - the slime will feel hard.
- Do the same thing, but very slowly – the slime will feel wet and runny.
What's going on?
Did you know?
Highly effective bullet-proof vests can be made by combining a strong fabric, such as Kevlar, with a stir-thickening fluid. Soaking the fabric in a stir-thickening fluid makes the fabric able to withstand the high impact of a bullet. When a bullet hits the fabric, the stir-thickening fluid quickly hardens, making the fabric stronger and resistant to the force of the bullet. However, slow moving objects pushing on the fabric will not cause the stir-thickening fluid to harden. This means the fabric is comfortable to wear and it is more protective against the sudden impact of a bullet compared with a slow-moving object such as a knife. Learn more...
Cornflour slime is a stir-thickening (dilatant or shear-thickening) fluid which means that its viscosity (runniness or tendency to resist flowing) changes depending on whether or not the fluid is being stirred. By stirring or punching the cornflour slime, you are applying a force. It is this ‘shear force’ which causes the slime to become thicker. As soon as the shear force is removed, the slime becomes runny again.
Most fluids are called ‘Newtonian’ because their viscosity does not change when a shear force is applied. For example, honey is a Newtonian fluid because stirring or applying another type of force to honey will not change its viscosity. However, changing the temperature of honey does change its viscosity. Heating honey lowers its viscosity so it is runny and quick to flow and cooling it increases the viscosity making it thick and slow to flow.
When cornflour slime is punched, a large shear force is applied. The cornflour particles lock together, increasing the viscosity, and the slime feels like a solid. When the slime is moved more slowly, a smaller shear force is applied. The cornflour particles have time to roll over each other with water flowing between the particles. In this case the fluid has a lower viscosity and flows like a fluid.
Test the properties of other common household food and other materials. Try mixing plain flour with water – does this behave in the same way as cornflour slime? Is tomato sauce a stir-thinning or stir-thickening fluid? A stir-thinning fluid becomes runnier when it is stirred. Try holding a bottle of tomato sauce upside-down. Does it flow out of the bottle? Now try hitting the bottom of the bottle and see what happens. A similar test can be done with a tube of toothpaste.