Stir cornstarch into water until it forms a thick, strange mixture that behaves like a liquid when poured slowly but turns solid under a sudden hit. Take turns punching, squeezing, and slowly sinking a hand into the mixture to feel the difference for yourself.
What you need
- cornstarch
- water
- a large bowl or tray
How to do it
- 1Stir roughly two parts cornstarch to one part water in a bowl until it's thick but still pourable.
- 2"Try punching it fast, then try sinking your hand in slowly -- what's different?" Let them test both.
- 3Roll a small ball of it between your palms and watch it turn liquid the moment you stop moving.
- 4Keep testing with different speeds and pressures, comparing what happens each time.
Variations
- If the mixture feels too runny: add cornstarch a spoonful at a time until it holds together when squeezed.
- How it ends: a final 'slowest possible sink' of a whole hand into the bowl is a satisfying way to close.
💡 Parent tip
Keep a bowl of clean water nearby for quick hand-rinsing -- oobleck dries into a fine powder on skin that brushes off best when caught early.
What your child develops
- Non-Newtonian fluid science — a genuinely counterintuitive material property, memorable well past this age
- Cause and effect — directly linking speed of force to the material's behaviour
- Sensory exploration — the mixture's shifting texture is a rich tactile experience on its own
Safety notes
- Not intended to be eaten. Clean up promptly, as dried cornstarch can be slippery on hard floors.
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