Create oobleck, the amazing slime that can be both a liquid AND a solid!!
You will need
- A bowl
- 3/4 cup of water
- 1.5 cup of cornflour
- Measuring cups
- Food colouring
- Spoon
What to do
Measure 3/4 cup of water and put it in a bowl.
Add food colouring to make your oobleck a fun colour.
Add 1 and a half cups of cornflour to the colourful water.
Mix the cornflour and water together with a spoon for 3-5 minutes until it reaches a thick consistency. From here on, this activity can get messy and slippery, we recommend putting down newspaper or butcher’s paper in your work area.
To make your oobleck act like a solid, quickly pick up the oobleck and roll it between the palms of your hands. You can also poke the oobleck quickly or hit it with a spoon. The more you poke, pat, hit or move the oobleck, the more it will act like a solid.
To make your oobleck act like a liquid, slowly stick your finger in the oobleck. Or, if you pick up your oobleck and roll it into a ball as described in step 5, as soon as you stop rolling the ball the oobleck will seemingly melt through your fingers like a liquid.
Once you are done experimenting, your oobleck is perfectly compostable. Don’t keep your oobleck longer than a day or it will go bad.
What’s happening
How can something be both a liquid and a solid? The short answer is that it can’t be. The long answer is that oobleck can act like both because it is what’s known as a “non-Newtonian fluid.” To explain what that means let me start with a concept called viscosity.
Viscosity is the measure of how easily a liquid flows, commonly described as how “thick” a liquid is. The thicker the liquid, the higher the viscosity. Water has a really low viscosity, while honey has a high viscosity because it’s a lot thicker. Both water and honey are “Newtonian fluids,” because they have a consistent viscosity when stress is applied to them. You can poke them, hit them, or squeeze them as much as you want, but their viscosity isn’t going to change. In contrast, a non-Newtonian fluid like oobleck changes its viscosity under stress.
In step 5 of this experiment, you saw that oobleck’s viscosity changes under stress. When you applied pressure to the oobleck by rolling and squeezing, it will form a solid ball that can be played with. This shows that it can have a high viscosity. However, as soon as you stop applying pressure to the oobleck, it seems to melt into a liquid and flow straight through your fingers, showing that it also can have a very low viscosity.
Oobleck’s viscosity changes because of the way the cornflour is suspended in the water. When there is no pressure applied, the cornflour and water move freely, and the cornflour particles just slide past each other. But when you apply pressure to the oobleck, the long cornflour particles get tangled together, which makes the mixture harden. This is what allows oobleck to act like both a solid and a liquid.
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