Pepper & surface tension science experiment : Fizzics Education


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Pepper & surface tension

Pepper & surface tension

Follow FizzicsEd 150 Science Experiments:

You will need:

  • White pepper
  • One white plate
  • Clear water
  • Detergent
  • A mess bucket and cleaning materials


Materials shown for the experiment, Plastic bowl, Bottle of detergent, Half full jar of water, White pepper.
1 Water from a Jug getting poured into a plastic bowl

Pour water into a shallow plate

2 Adding Pepper to the plastic bowl of water

Sprinkle white pepper over the surface of the water.

3 Adding detergent to a plastic bowl of water and pepper.

Add a drop of detergent into the center of the plate and watch the pepper spread out!

4 A man using a pipette to drop blue coloured water onto a taught strong that is suspended over a tray

Get the Unit of Work on Water Science here!

  • Explore the water cycle
  • Learn about cohesion, adhesion & capillary action
  • From water currents to floatation, join us to explore water science!

Includes cross-curricular teaching ideas, student quizzes, a sample marking rubric, scope & sequences & more

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5 Students dipping bubble wands into buckets
6 Teacher showing how to do an experiment outside to a group of kids.

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– Help students learn how science really works

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What is happening?

All liquids have surface tension along the surface of a liquid, caused by inter-molecular forces within the liquid pulling liquid molecules together. Because of surface tension, liquid surfaces act like a kind of ‘skin’, able to support small insects and materials on their surface.

Your detergent molecules reduced the water surface tension in the centre of the plate and so the higher surface tension at the edge of the plate pulled the pepper outwards. This is an example of the Marangoni effect in action. The Marangoni effect describes how a liquid with a high surface tension pulls more strongly on the surrounding liquid than a liquid with a low surface tension. If you change the surface tension of some parts of the liquid you introduce a difference in surface tension or ‘gradient’. A presence of a surface tension gradient will cause the liquid to flow from areas of low surface tension to high surface tension.  Put simply, the water surface was pulled outwards!

A man with a glove above a liquid nitrogen vapour cloud

Variables to test

More on variables here

  • Hot vs. cold water
  • What happens when you use different liquids?
  • Different size granules on top of the water

You can use surface tension to make cardboard boats shoot across water!

Soap powered boat science experiment - adding detergent to boat


Learn more!


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