How to: make a liquid that's also a solid
Mark Miodownik, presenter from Dara O Briain's Science Club on BBC Two, reveals how you can perform simple science experiments at home. This weird slime is easy to make and acts like a liquid but behaves like a solid when you hit it.
Throw a rock into some water and like most liquids, it'll splash everywhere. But some liquids, like quicksand for instance, act differently depending on how much force you apply to them. They're called non-Newtonian fluids and they have some very unusual properties. See for yourself by mixing up some cornflour slime...
Things you'll need:
- Large mixing bowl
- Measuring jug
- Cornflour (450g / 16 oz)
- Water (475ml / 16 fl oz)
- Clear re-sealable storage bag
- Uncooked egg
- Food dye (optional)
- Plastic disposable gloves (optional)
How to do it:
Making cornflour slime can get a bit messy, so make sure you wear an apron to protect your clothes.
It's easy to make non-Newtonian slime using just cornflour and water.
When you mix cornflour with water, the large cornflour particles remain 'suspended' (float around) in the liquid.
Cornflour slime is thick because the particles are packed very close together, yet they are still able to slip past each other.
When you stir the mixture slowly it acts like a liquid because the suspended particles have time to move past each other.
Yet when you put sudden stress on the mixture, by rolling it for example, the water quickly flows out of the area but the particles do not have enough time to move out of the way.
The cornflour particles temporarily stay packed up where they are, which makes the slime act like a solid.
Place 450g / 16 oz of cornflour into a large mixing bowl.
Add 475ml / 16 fl oz of water and use your hands to mix it into the cornflour. If you want to make coloured slime, add a couple of drops of food dye to the water first. You can wear disposable plastic gloves to avoid staining your hands.
Keep mixing until the cornflour and water have blended together and the slime is the consistency of honey. You can add more cornflour to make the slime thicker, or more water to make the slime thinner.
Now here are a few things you can do with it…
Try punching the slime, making sure withdraw your fist back quickly. You would expect most fluids to splash, but you'll find this mixture instantly turns hard. This is because, under the force of your punch, the water in the slime quickly flows away from the site of impact and leaves behind a very dense patch of cornflour particles in front of your fist.
Now try scooping some of the slime into your hand and rolling it into a ball between your palms. As long as you keep pressure on it, the solid mixture will keep the shape of the ball. Stop rubbing however and it soon trickles back into the bowl as a liquid.
Non-Newtonian fluids in everyday life
- Quicksand has similar properties to the 'shear thickening' slime mixture. If you struggle to escape quicksand, you apply pressure to it and it becomes hard - making it difficult to escape
- Ketchup and some other sauces are 'shear thinning' liquids. This is why they stay almost solid in the bottom of a plastic bottle, but if it is squeezed the sauce pours out easily
- Earthquakes can turn certain types of shear thinning clays into runny liquids through sudden movement. This is called 'liquefaction' and can cause houses to sink or collapse
- Armour containing shear thickening fluids has been shown to stop bullets. The liquid allows the armour to conform to a person's body shape, but becomes solid and resistant when struck
Non-Newtonian fluids, like cornflour slime, are really good at absorbing and dissipating energy. You can test this yourself by spooning some of the slime into a re-sealable storage bag. Stop when the bag is two-thirds full, then gently push an uncooked egg into the mixture.
Find a clear area where you can safely drop the bag from a height of around 8-12 feet, or 2.5-3.5 metres. Make sure you seal the bag tightly before you let go.
You would expect the egg to break if it was suspended in a Newtonian liquid that has a constant viscosity (resistance to flow), like water for example. However, because of its non-Newtonian properties, as the slime hits the ground it forms a solid around the egg. This means that the force of the fall is evenly distributed around the shell's surface and it stays intact. How high can you drop it until the egg breaks?
IMPORTANT: Don't pour your slime down the sink as this could clog the pipes. Instead spoon the mixture into a zip-lock bag, fasten it tightly and dispose of it in a bin.
Cornflour slime is an example of a 'shear thickening' substance, but there are other types of non-Newtonian liquid. Some can get thicker or thinner, some instantly and some over time:
|Type of behaviour||Description||Example|
Viscosity increases with increased stress
Viscosity decreases with increased stress
Viscosity increases with stress over time
Viscosity decreases with stress over time
Send pictures of your cornflour slime to @BBCScienceClub
Dara O Briain's Science Club is at 8pm, Thursdays throughout August 2013 on BBC Two