Oobleck (magic goo)
Cornflour and water make a weird material: hard as wood when you hit it, runny when you let it drip through your fingers.
Age : from 18 months, always with a grown-up
Materials
- 2 cups of cornflour : Cornstarch or similar.
- 1 cup of water : Pour it in bit by bit.
- Food colouring : Optional.
- A big dish or basin
- Spoons, a funnel, small figures : To play.
Steps
Make and play
- Pour the cornflour into the dish.
- Add the water (and colouring) bit by bit, mixing with your fingers.
- The right texture: when you tap it, it resists; when you pick it up gently, it flows.
- Too runny? A little cornflour. Too hard? A few drops of water.
- Punch it hard, then lay your hand on it gently: it sinks in!
- Make a ball by rolling it fast between your hands, then stop: it melts.
It's a "non-Newtonian" fluid. Tiny grains of starch float in the water. When you push fast and hard, they jam together and the goo turns hard. When you go slowly, they have time to slide and it flows like a liquid.
Hide small figures in it and "rescue" them with a spoon.
If it goes wrong
- All runny : Add cornflour a spoonful at a time.
- All hard and crumbly : A few drops of water.
- It dried out : Add a little water and mix again.
Safety
- Never pour it down the sink: it can block the pipes. Let it dry and put it in the bin.
- Even though it's kitchen ingredients, don't eat it.
- With toddlers, a grown-up stays close the whole time.