Sunday 19 August 2018

5 Minute STEM Activity 17: Solids that pour. Liquids that can be piled up.

Normally we need to add or remove heat to change something from a solid, to a liquid, to a gas. Non-Newtonian Fluids are a liquid when left alone, but they behave more like a solid when we try to move them quickly or apply pressure... It can pour, but if you hit it, it can feel as hard as rock.

Solids That Are Liquids.
Non-Newtonian Fluids.

A Non-Newtonian Fluid is a fluid that breaks Newton's Law Of Viscosity. Viscosity is what we would call 'thickness' (for example, oil is 'thicker' than milk) and it usually affects how quickly something will move. Non-Newtonian fluids will pour, but they don't quite follow the rest of the standard rules for liquids.

A shallow bowl or deep plate
Something small to mix in
Something to stir with
Cornflour /corn starch /maize starch or custard powder (they're all very much the same thing with flavourings or a different name).

Cornflour and water mixed together create a non-Newtonian fluid, as does salt with a very small amount of water added.

We used 4 big heaped teaspoons of cornflour

We used 6 teaspoons of salt

Add water very slowly, a few drops at a time to the cornflour, and one drop at a time in salt. Make your mixtures into a smooth paste.

The paste will behave very strangely. You'll see this even while you are still mixing.

If your paste is really stiff and doesn't move, add a drop or two more water and mix again. Repeat until your paste works perfectly. Careful not to add too much water.

A non-Newtonian fluid will heap up like a solid, then collapse into a pool with a flat surface - just like water or other liquids. You may have to wait a second or two...

Try some tests. What happens when you tip the plate? What happens when you hit the fluid with a spoon or your hand? Does it splash?

Can you pick up all of your fluid at once? What happens once you've picked it up?

The salt mixture is not quite as fun an example as the cornflour mixture, which is known as Oobleck in America. Cornflour (corn starch) has no gluten, so any spills won't leave a sticky mess and this is a great thing for small children to play with because it's edible - although not really very tasty.

Toothpaste and Ketchup are also non-Newtonian fluids. If you want to get ketchup out of the bottle more quickly, carefully close the lid and turn it upside down. Don't let go, but give it one good downwards slam, as if you are banging in an imaginary wooden stake with a ketchup bottle hammer. The ketchup gets moving more quickly as a big lump than it does as a flowing liquid.  It behaves more like a solid.

Slime is non-Newtonian and so is quicksand. In theory if you find yourself in quicksand, you can run away as long as you land each step with a thud and keep moving. Remember that fact... it might help one day...

You can find all of the 5 Minute STEM Activities here...  None cost more than pennies or need anything you won't find in most homes (save your cereal boxes).

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