Slime

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 going on?

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.

Special Safety advice

Playing with this with your hands is perfectly safe (although if you are using custard it can leave your hands a little yellow). If you are planning a larger scale experiment and walking on this, it can act like quick sand: make sure it is not too deep or you will become trapped, and never attempt to submerge your body in it. If you are planning to walk across it be warned it can be very slippery.