Activity

DIY Oobleck

Mix up a goo that turns firm when you squeeze it and drips like a liquid the moment you let go.

Ages: 7–11
Duration: 45 minutes

What kids build

A bowl of homemade oobleck, plus notes on which cornstarch-to-water ratio behaved the most like a solid under pressure and the most like a liquid at rest.

Materials we bring

Cornstarch, 1.5 to 2 cups per team
Water, 1 cup per team
Food coloring
Mixing bowl
Spoon or spatula
Measuring cup
Tray or table cover for spills
Paper towels for cleanup

How we run it

01 Set up tables with materials for each team.
02 Put a tray or table cover under each team's workspace. Oobleck is messy, and that is half the fun.
03 Tell kids they are materials scientists today and their mission is to mix a goo that can act like a solid and a liquid at the same time. Best batch wins.
04 Pour 1 cup of water into the bowl. Add a few drops of food coloring and stir until the color is even.
05 Slowly add cornstarch, about 1.5 to 2 cups, while stirring the whole time.
06 Keep mixing until the goo turns thick and smooth. If it is too runny, add a little more cornstarch. If it is too dry, add a splash more water.
07 Scoop some up and squeeze it fast in your hand. Notice how firm it feels while you press.
08 Stop squeezing and let it sit in your open palm. Watch it ooze and drip like a liquid.
09 Test it every way you can. Poke it slowly, then quickly. Tap the surface. Try to roll it into a ball. What changes?
10 Write down how your batch looked, felt, and moved in the data table.
11 Compare teams. Which recipe made the best oobleck, and what did they do differently?
12 Clean up with paper towels and toss leftovers in the trash, never down the drain. Cornstarch can clog pipes.

Kids mix cornstarch and water into oobleck, a goo that turns firm when you squeeze it and flows the instant you let go. Teams tune their ratio, test how it answers slow and fast pokes, and compare batches. The best scientists observe closely, tweak the recipe, and run it again.

Real-world connection

The science hiding in a ketchup bottle

Oobleck is a non-Newtonian fluid, which is a fancy way of saying it changes how it flows depending on how hard you push it. Squeeze it fast and it acts solid. Let it rest and it runs like a liquid. The same trick shows up in the ketchup that only pours once you shake the bottle and in the toothpaste that stays put on the brush until you press the tube. Engineers even build cornstarch mixes that stiffen the instant they take a hit, so they can soak up sudden impacts.

Go deeper

Extension ideas

Ratio lab

Make one batch with more cornstarch and one with more water. Which one feels most solid when you punch it and most runny when you let it rest? Write down the recipe that wins and try to beat it.

Slow versus fast

Poke the oobleck slowly, then jab it fast. Does it react the same way both times? Kids figure out that it is the speed of the force, not the size of it, that decides how the goo behaves.

Bring this to your space

Want the DIY Oobleck at your library or school?

Tell us your space, your age range, and rough timing. We will come to you. Materials are on us.

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