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

    Surface Tension of Water Demonstration

    April 17, 2019 By Emma Vanstone 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.

    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!

    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 disrupts the surface tension of the milk, which makes food colouring spread out just like the pepper and water.

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

    Another surface tension experiment is where you 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 paperclip 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 the weight of the paper clip 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 January 18, 2023 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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