Cornflour slime: sink your fingers into this bizarre oobleck

Cornflour slime: sink your fingers into this bizarre oobleck

Cornflour slime: sink your fingers into this bizarre oobleck 1024 681 Looking out Loud
  • In brief: Make a super cool slime that’s hard when you hit it, and runny when you play gently.
  • Time needed: 5 minutes to create, lots more time to play
  • Skills encouraged: Experimentation, Curiosity
  • Age: 4 to adult

  • Imagine running your fingers through your hair, or a pile of sand on the beach. Now imagine squeezing a ball of soft cotton, or pink cornflour slime.

    What, you’ve never felt cornflour slime? Then you have to try this.

    This is some of the most bizarre stuff we’ve ever felt. It’s kind of runny and slimy, kind of solid and chalky. Exactly how it feels depends on how you touch it. Hit it and it feels hard. Hold it gently and it gets runny. Really, this is cool.

    Here’s what you need for cornflour slime:

    • Cornflour (start with a cup, and have more on hand)
    • Water in a big cup or jar
    • Food coloring (we used red)
    • Big bowl and spoon
    • Newspaper or something to cover the table
    • Latex gloves (optional; not as cool but the food coloring can stain hands)

    We made our first batch in a small plastic container with a wooden stir stick and it was enough. But next time we’ll use a bigger bowl to make even more. Whatever you use it cleans easy.

    Here’s how to make cornflour slime:

    1. Add a couple drops of food coloring to your water and stir it in.
    2. Dump some cornflour into the bowl. Start with a cup or two, don’t overthink the amount.
    3. Pour a little water in your cornflour bowl and mix it together with the spoon.
    4. Keep adding water and stirring until you’ve got a thick slime-looking stuff.
    5. Start playing—squeeze it, hit it, poke it, scoop it into your hands. Cool right?

    The first time we did this, it was a mix of excited “Wow!”s and silent stares, as we curiously observed the different ways the slime feels depending on how you touch it.

    As you play, experiment by adding a little more water. Now a little more cornstarch.

    Here’s a few other things to try:

    • Hit a pile of the slime with your fist, or poke it strongly with a couple of fingers. The slime feels hard, like a solid.
    • Press your finger very slowly into the slime, or dump it carefully into your hand. The slime feels wet and runny, like a liquid.
    • Dump it in your hand and quickly squeeze. The slime clumps together and feels rubbery, like a little stress ball. Now relax your grip, and watch the slime ooze through your fingers.

    What the oobleck is going on here?

    Cornflour is made of little particles. But unlike water particles, which are round and smooth like little balls, cornflour particles have jagged edges. So how runny the slime is—its viscosity—depends on the force applied to it.

    When you apply a hard force to the slime—by stirring or punching it—the cornflour particles clump together and make the whole substance feel thicker. When you apply a soft force, like gently pushing your finger through the slime, the cornflour particles roll over each other, giving it that gooey flow.

    This is different than other fluids like water or honey. Most liquids are called “Newtonian” because their viscosity doesn’t change by applying force. If you smack a bowl full of water, the water splashes everywhere. Honey is the same runny if you gently spread it across your bread or violently throw it against the wall (I’d love to actually try this, but I’m afraid my wife would kill me).

    But cornflour slime is a “non-Newtonian” liquid. It’s sometimes called a “shear-thickening fluid” (and also known as oobleck) because its viscosity changes when shear force is applied. When you punch cornflour slime, that shear force smashes the particles together and its jagged particles get locked together. With a soft force, the water in the cornflour flows around the particles, allowing the goop to run.

    Is a bulletproof vest made of cornflour slime?

    No, police don’t wear clothes made of cornflour. But some kinds of liquid body armor work in the same way as our cornflour slime. They both bank on the discovery of non-Newtonian fluids.

    These bulletproof vests combine strong fabrics, like Kevlar, and a shear-thickening fluid. Basically, the Kevlar is soaked in a special shear-thickening fluid, allowing it to be soft or hard depending on the force applied. When no forces are applied, the vest stays soft, making it comfortable to wear around (at least more comfortable than medieval chainmail). When hit by a high-speed bullet, the fluid quickly thickens, giving extra impact protection and saving lives.

    Oobleck cornflour slime running over fingers