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Home » Science Experiments for Kids » Surface Tension of Water Demonstration

Surface Tension of Water Demonstration

Modified: Apr 7, 2025 · Published: Apr 17, 2019 by Emma Vanstone · This post may contain affiliate links · 3 Comments

These super simple investigations are great for demonstrating the surface tension of water.

What is surface tension?

Surface tension is a force which causes a layer of liquid to behave like an elastic sheet or skin.

Water molecules are more attracted to each other than other molecules, as water is a polar molecule. The positive hydrogen end of one molecule is attracted to the negative oxygen end of another water molecule. The surface water molecules only have air above them, so they are pulled down, creating surface tension.

The high surface tension of water allows insects to walk over it. Pond skaters have long, hairy legs, allowing them to spread their weight over a wide area. They press very gently on the water’s surface so as not to break through it.

Pond Skater on water - surface tension
Pond skaters on water

In a container of water, molecules below the surface are pulled together ( or attracted to each other ) equally in all directions, but those on top are pulled together more tightly, as they don’t have water molecules above them; this draws them together to form a ‘skin’. It is this skin ( surface tension ) that stops items on the surface from sinking.

Surface Tension Holes Experiment

You’ll need

A big bowl of water

Some ground pepper (black so you can see it) or any other ground product with colour

A bowl of water with a layer of black pepper sprinkled on top for a surface tension activity

Washing up liquid ( dish soap )

Method

Once the water settles, sprinkle the ground pepper over the top.

Drip some washing-up liquid in the middle of the bowl and watch what happens.

A hole appears in the centre as the pepper moves outwards. This is your surface tension hole!

If you want to repeat the demonstration, you’ll need to wash out the bowl thoroughly to remove any traces of the dish soap (washing-up liquid ), or the effect will be less dramatic.

hole in a layer of water coated in pepper for a surface tension investigation

Why does this happen?

The surface tension hole is caused by the washing up liquid reducing the surface tension of the water. This allows the particles of water at the surface to spread out, starting from where the washing-up liquid was added.

More Surface Tension Experiments for Kids

Frugal Fun for Boys has an excellent surface tension investigation using a coin and different liquids!

You can use washing-up liquid to disrupt the surface tension of water to race lolly sticks.

In a magic milk experiment, the washing-up liquid ( dish soap ) disrupts the surface tension of the milk, causing food colouring to spread out like pepper and water.

magic milk investigation - cool science experiments for kids
Magic milk experiment to demonstrate surface tension

Another idea for a surface tension experiment is to make a shape on the surface of the water with cocktail sticks and drop some washing-up liquid in the centre to force the sticks apart.

Try filling a bowl half full with water and carefully placing a paper clip on the top, so it floats. Mix a little washing-up liquid in a cup with water and gently pour it into the bowl. The paper clip will sink as the water can no longer support its weight after the washing-up liquid disrupts the surface tension of the water.

Science concepts

Surface tension

Collage of images related to surface tension. Pond skater, raindrop and magic milk investigation
Surface Tension Experiments

Last Updated on April 7, 2025 by Emma Vanstone

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Safety Notice

Science Sparks ( Wild Sparks Enterprises Ltd ) are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources. Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources.

These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.

Reader Interactions

Comments

  1. hw

    October 16, 2011 at 3:00 pm

    Great activity, I am going to try it with my daughter! I love how you call it “washing up liquid” – I call it that too. 🙂

    Reply
    • ScienceSparks

      October 16, 2011 at 9:26 pm

      Thanks, glad you like it!

      Reply
  2. Aimee

    October 21, 2011 at 6:01 pm

    So many great ideas come form this blog! Thank you for linking up to the The Sunday Showcase

    Reply

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