Strange liquids – introduction
Liquid is one of the states of matter, and viscosity is a property of liquid. Some liquids display strange behaviour because their viscosity makes them flow differently to ‘normal’ liquids.
Honey
Honey is an example of a non-Newtonian fluid – a fluid that changes its behaviour when under stress or strain.
When we think of a liquid, we tend to think of something like water. When you pour the liquid into a cup, it takes on the shape of the container. This is one of a liquid’s properties.
Another property of a liquid is its viscosity – how easily it can be deformed and how fast or slow it flows. Some liquids are so viscous they flow very slowly, like honey, custard or tomato sauce.
Custard
Custard, a delicious pudding and also an example of a non-Newtonian liquid that changes its viscosity under stress.
Another name for ‘normal’ liquids is Newtonian fluids, but some liquids behave so strangely they are called non-Newtonian fluids. Non-Newtonian fluids change their behaviour when they are under stress or strain, which means that some sort of force is applied on them. A very famous non-Newtonian fluid is a mixture of cornflour and water – when a force is applied, its viscosity gets very high momentarily.
Oobleck
Oobleck – a cornflour and water mixture named after a substance in a Dr Seuss book – initially behaves like a liquid or a jelly. However, when you squeeze it in your hand, it behaves like a solid for a short time. It becomes more viscous when agitated or compressed and belongs to a subset of non-Newtonian fluids called dilatants. When a force is applied to a dilatant, its viscosity increases.
Meet the scientists
Strange liquids are fascinating. Scientists like Dr Michael Walmsley from the University of Waikato are studying different fluid properties. Even younger scientists studied non-Newtonian fluids as substitutes for cricket pads. Of course, one of the most famous fluid scientists is Sir Isaac Newton.
Take up the challenge
The student activities about strange liquids are some of the most popular on the Hub! Try some of the ones below:
Racing marbles compares the viscosity of common household substances by measuring how fast marbles move through the liquids.
Slumpy solids or lumpy liquids explores a range of common household substances to determine if they have the properties of a solid, a liquid or both.
Different liquids
Water, milk, juice, oil, tomato sauce, honey and custard are all liquids, although some of them are special liquids called non-Newtonian fluids.
Exploring states of matter uses concept maps to explore current ideas about states of matter.
Danger – quicksand! uses a concept cartoon and ooleck to plan and carry out an investigation.
Walking on custard aims to help teachers use video as an effective teaching tool.
In this unit plan aimed at middle primary, experiment with various liquids, including non-Newtonian fluids, to see how their viscosity is changed by stress or force. Consider how science knowledge continues to change with new discoveries. This introduces the idea that investigations in science often use models to find evidence to answer questions about experiences in our world.
I've used the Learning Hub for the matter activities – getting students to look at different states of matter and also the 'strange liquids' task for the year 9s to get students to realise that in science, everything isn't so clear-cut.
Larua Bennet, teacher
See our Strange liquids Pinterest board for more resources.
