Monster Goo (Oobleck)

Ages 3+ with an adult10 minutes, plus play timeMess: High: cover the table and floor

Grown-ups: please supervise this experiment the whole time. Read the safety notes first.

Mix cornflour and water into a green monster goo that runs like a liquid but turns solid when you punch it.

WOW FACT

The name oobleck comes from a 1949 Dr Seuss book, Bartholomew and the Oobleck, where a sticky green goo falls from the sky.

🧰 What you'll need

CornflourThe baking-aisle kind, about 2 mugs.
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WaterAbout 1 mug, straight from the tap.
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Green food colouringOptional, for that monster look.
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A large bowl or deep trayPlenty of room for poking and squeezing.
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A spoonFor slow stirring.
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Newspaper or a wipe-clean clothTo keep the table and floor clean.
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✨ Want to go further? (optional)

Kids' messy play trayA deep tray keeps the goo off the table.
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Safety goggles for kidsKeeps flicks of goo out of eyes, and gets children into good scientist habits.
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Children's science experiment bookDozens of easy experiments for rainy days.
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What to do

Cover the table (and the floor under it) before you start.
Tip the cornflour into the bowl. Add a few drops of green food colouring to the water.
Pour in the water a little at a time, stirring slowly, until all the powder is wet.
Aim for goo that runs when you tilt the bowl but feels firm when you tap it hard. Too runny? Add a spoonful of cornflour. Too stiff? Add a splash of water.
Punch the surface quickly, then rest your fingers on it slowly. What's different?
Scoop some up and roll it into a ball in your hands, then stop rolling and watch it ooze away.
When you've finished, leave it in the bowl to dry out, then scrape it into the bin.

What's going on?

The cornflour doesn't dissolve. Its tiny starch grains just spread out through the water, which is called a suspension. Move slowly and the water lets the grains slide past each other, so it flows like a liquid. Hit it hard and fast and the grains jam together, so for a moment it acts like a solid. Scientists call this a non-Newtonian fluid, because how runny it is changes with how hard you push it, not just with temperature.

Safety notes

Never pour cornflour goo down the sink or toilet: the cornflour settles out and can block pipes. Let it dry, then scrape it into the bin.
Wipe goo off hands and bowls with kitchen roll into the bin before washing up.
Spilt goo makes floors slippery: wipe it up straight away.
Food colouring stains clothes and surfaces: wear old clothes.
Don't eat the goo, and keep it away from eyes.