Indoor activity
Cornflour Oobleck
Make a mysterious goo that's solid when you squeeze it but flows like liquid the moment you relax — is it magic or science?
Materials
- Cornflour
- Food Colouring optional
- Large Bowl
- Spoon
Illustrated Steps
Measure the Cornflour
Pour two cups of cornflour into a large bowl and make a well in the centre ready for the water.
Slowly Add Water
Add one cup of water a little at a time, stirring as you go. Stop when the mixture is very thick and hard to stir.
Add Food Colouring
Drop a few drops of food colouring into the oobleck and fold it in slowly. Watch it shift between solid and liquid as you stir!
Squeeze and Play
Punch it fast — solid! Let your fist sink in slowly — liquid! Roll a ball and open your hand. Watch it melt away like magic.
What You’ll Create
Oobleck — a strange, gooey mixture that behaves like both a solid and a liquid! Squeeze it in your fist and it feels rock hard. Open your hand and it drips away like liquid. Add food colouring to make it extra dramatic.
How to Set It Up
Step 1: Measure the Cornflour
Pour two cups of cornflour into a large bowl and make a well in the centre. This is where you’ll add the water in the next step.
Step 2: Slowly Add Water
Add one cup of water to the cornflour a little at a time, stirring as you go. Stop when the mixture is very thick and hard to stir — do not add too much water or it becomes too runny.
Step 3: Add Colour
Drop a few drops of food colouring into the oobleck and fold it in slowly. It will look dry, then suddenly liquid, then dry again — that’s completely normal!
Step 4: Squeeze and Play
Punch the surface hard — it’s solid! Let your fist sink in slowly — it’s liquid! Roll it into a ball and open your hand — watch it melt away. Try pouring it from hand to hand.
Have fun!
Try experiments: hit the surface sharply with a spoon. Slowly drag your finger through. Try pouring it between two bowls. Does it feel different when warm versus cold? What happens if you add a little more water?
Why It’s Amazing
Oobleck is a non-Newtonian fluid — its viscosity changes based on the force applied. Cornflour particles pack tightly under pressure, making it solid, but flow freely under low force. The same science is used in body armour, shock-absorbing speed bumps, and even some specialist dance floors!
Pro Tips
💡 Two cups cornflour to one cup water is the golden ratio — too much water makes soup, too little makes crumble. 💡 Oobleck dries out over time — add a tiny splash of water to refresh it. 💡 Play on a tray or outside — the dried bits brush up easily.