Making non-newtonian fluids
In this laboratory session, we will mix water with cornflour to explore weird materials that are not quite liquid but not quite solid either.
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This experiment can get quite messy!
You will need
Cornflour
Water
Weighing scales
Food colouring (optional)
Making non-newtonian fluids
Weigh ingredients
Using the Weighing Scales, measure out 20g of Cornflour and 16g of tap water.
If you would like to make more or less, the ratio is 5g of cornflour to every 4g of water
Mix the ingredients
In a bowl, mix the cornflour and the water together (along with some food colouring if you want!) until the cornflour is fully combined with the water.
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If you find that the mixture is too sticky when you try to mix it together then try stirring slower.
Things to try
Try quickly tapping your finger on the liquid. What happens and how does it feel?
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Try slowly tapping your finger on the liquid. What happens now and how does it feel?
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What you should find is that when you quickly tap on the surface of the liquid it feels hard maybe a bit springy or spongy. But when you slowly tap the liquid, it should feel a bit sticky or kind of like quicksand. Why do you think this is?
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Can you scoop some into your hand and roll it around like a ball?
Shake it up
Try putting some in a shaker bottle with a shaker ball.
When you shake it, does the shaker ball move?
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Try shaking it at different speeds and see what happens!
How does this work?
When the cornflour is mixed with the water, the water fills in the gaps between the individual cornflour particles.
When you apply a small force to the mixture it lets the particles to move around each other, using the water in between to act like a lubricant. But if you apply a larger force quickly, the water between the particle gets pushed out and the particles hit each other – friction between them stops them moving and it behaves like a solid. This cornflour/water mixture is an example of a Non-Newtonian fluid.
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These weird fluids change how they act depending on how quickly a force tries to make them move and how strong that force is. In this case, the cornflour/water mixture behaves like a solid when it is tapped quickly (at high frequency) and behaves like a liquid when tapped slowly (at low frequency).
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For example, here we have three different liquids in a shaker bottle with a shaker ball. The first is water, the second is golden syrup and the third is our cornflour/water mixture we made earlier. We then shook them and recorded it using the slow-motion feature of our smartphone camera.
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Shaking the water
Shaking the golden syrup
Shaking the corn flour mixture
As you may notice, the water moves around a lot, the golden syrup moves a little bit and the cornflour/water mix moves a little when shaken slowly but not at all when shaken fast.
A quick side note on water and golden syrup. As we now know, the cornflour mixture is non-Newtonian which changes its properties depending on the force and how quickly it is applied. Whereas water and golden syrup are Newtonian fluids meaning that they don’t change their properties depending on how quickly or strongly a force is applied.
Although they are both Newtonian fluids, golden syrup is a lot thicker than water which is why you can drizzle golden syrup over your pancakes but if you did that with water it would be a soggy mess (Also golden syrup super tasty!). The difference between them is how much force is required for them to start flowing and this property of fluids is called Viscosity.
If a fluid has a high viscosity (like golden syrup) then it takes a higher amount force to get it to start flowing. On the other hand, if a fluid has a low viscosity (like water) it takes a lower amount of force.
Unlike the non-Newtonian fluids, once the force is great enough the Newtonian fluids will flow regardless of whether the force is applied quickly or slowly. This is why we have to shake the bottle really hard to get the golden syrup to move but only a little when we have water.
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Now back to non-Newtonian fluids. There are many different non-Newtonian fluids that you will have come across in your day-to-day life without even realising! Here are a few examples of everyday non-Newtonian fluids:
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Ketchup
Toothpaste
Custard
Paint
Shampoo
Saliva
Slime
As you’ve probably guessed, not all of these examples react the same as the cornflour/water mixture and they even behave differently to each other. Figuring out how these fluids behave is called Rheology, and is very important to a wide range of scientists including physicists, engineers, and food-scientists.
