Kitchen science: investigate non-Newtonian fluids

Experimenting on ketchup in a funnel

What’s a non-Newtonian fluid?


Liquids and gases are fluids - they flow and take the shape of whatever container they are in.

You can describe how easily fluids flow using the word viscosity e.g. water flows more easily than syrup because it has low viscosity.

How viscous a fluid is can be changed by temperature. For non-Newtonian fluids it can also be changed based on the force applied to it e.g. whether they’re stirred or not.

Ooblek (a mixture of cornflour and water) is one of the most commonly known non-Newtonian fluids. However, you may be surprised to learn that there are lots of them lurking in your kitchen. In this experiment you’re going to investigate the ways in which they are similar or different.

For this experiment you will need:


  • Sandwich bags
  • Scissors
  • Drinking glasses
  • Small bowls
  • Cornflour
  • Water
  • Tomato ketchup
  • Spoons
  • Pencil
  • Paper

Preparing the experiment

Creating funnels from sandwich bags

1. Lay two sandwich bags one on top of the other and snip off one corner. You’re lining them up so that both bags have roughly the same sized opening - don't make it too big.

Plastic funnel propped up in a tall glass

2. Place each bag inside a drinking glass with the opening almost at the bottom. Fold the edges of the bag over the sides of the glass to hold your funnel in place.

3. In one of the small bowls create Ooblek by mixing 2 parts cornflour to 1 part water.

4. In the other bowl put two parts tomato ketchup and 1 part water before mixing thoroughly.

Conducting the experiment


1. Tip the ketchup mixture into one of the funnels and watch what happens. Note down your observations of how the fluid flows.

2. Whilst there is still plenty of ketchup in the funnel stir the mixture (apply force) and the stop. Note down what you observe. Does the speed of the flow change? Does the thickness of the fluid appear to change?

3. Repeat steps 1 and 2 with the second funnel and the Ooblek mixture.

Analysing your results


Once both funnels have emptied take some time to look over your observations and think about what you have learned.

  • Did stirring affect the fluids? In the same ways?
  • How did the flow of each fluid change?

  • Do the two fluids behave in the same way?

You might also like to apply some more scientific terms to your results. Shear-thinning fluids flow more easily when shaken or stirred. Shear-thickening fluids behave in the opposite way. How would you label each of the fluids you used in your experiment?

In what ways do you think the properties of the tomato ketchup help you when getting it out of the bottle and using in on your food? You may be interested to read this article for some more ideas…


Want to continue the experiment?


You may like to set up some more funnels and conduct the same experiment with different fluids e.g. mayonnaise, yoghurt or mustard.

You could experiment with changing the ratio of fluid to water and see how that affects each fluid’s viscosity.

Can you think of a way to test whether heat/cold also affects the viscosity of these fluids?