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What is Oobleck?

This week we have been exploring some interesting mixtures like Oobleck, a non-newtonian fluid, in our Mix it Up theme.

Before we talk about Oobleck, let’s start with what a mixture is. Everything around us is made up of atoms and molecules (2 or more atoms joined together), they are so small we can’t see them until many millions of them are joined together. Sometimes we can add 2 or more different materials together and their molecules will easily mix- like when we dissolve sugar or salt into water. Sometimes though these molecules will not mix at all- like oil and water. Other times the mixtures we make will behave in unusual ways like the non-Newtonian fluid Oobleck.

It’s also important for us to talk about the different phases, or states of matter and how the atoms behave in each. The atoms that make up the objects around us move, either quickly in a gas, or very slowly in a solid. We can change the phase of matter using heat, so by heating up a block of ice the atoms that form it will begin to move more quickly which means it melts into water. If we heat water the atoms will move even faster, which creates water vapour (steam) which is a gas.

The atoms in liquids move around enough to allow the liquid to flow, these are called Newtonian fluids. However, the atoms in non-Newtonian fluids move enough to let the liquid pour and change shape but only if it is done slowly. If you move or stir it too fast the atoms crash into each other which makes it solid, until you stop moving/ stirring the material.

Back to Oobleck then, it’s a simple mixture of water and cornflour, yet it doesn’t behave as we expect.

One of my Explorers told me:

“I thought I had made a mistake when it was hard then scooped it out and it turned to liquid- mind blown but love doing things that impress a 7-year-old”

Here’s what you need to make Oobleck:

  • bowl
  • spoon
  • cornflour (1 cup)
  • water (1/2 cup)
  • food colouring (optional)
  1. Add one cup of cornflour into your bowl
  2. Stir in the water gradually and mix
  3. You need to keep stirring until all the lumps are removed
  4. Add more water as needed, but make sure you don’t add too much!
  5. You are aiming for a mixture that will appear solid when you roll it between your hands but runs between your fingers when you let it go.
  6. Investigate what happens when you change the quantities of water and cornflour.

So why is it liquid and solid at the same time? Remember, with a non-Newtonian fluid, the viscosity (thickness) is not always the same- sometimes it seems solid and other times it seems liquid depending on how much pressure we put it under. If you stir the mixture quickly with a spoon it becomes solid, as the cornflour particles are compressed together. As you stop stirring the pressure eases which makes it less viscous.

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