Science for kids – Soap boat water experiment – ExpeRimental #14

Comedian Rufus Hound and his son Alby make soap powered boats and learn how soap affects the way water molecules hold onto each other.
For info sheets and printable boat templates, click here:

ExpeRimental is a series of videos showing fun, cheap, simple science activities to do with 4-10 year olds. Subscribe for regular science videos:

Rufus and Alby do a science magic trick with some pepper (or oregano, if that’s your flavour), washing up liquid and water. Watch the flakes shoot across the water at the touch of a finger. They experiment with different liquids, investigating how substances around the house affect the surface of water. The dramatic effect you see is because the soap weakens the pull that water molecules have on each other. As a result, as the soap spreads over the surface of the water, the water is able to pull away, taking the oregano or pepper with it.

This amazing trick can be used to make a great activity. Cut a boat shape out of a drinks carton, with a little space at the back (for the ‘engine’). When you add a drop of soap in the hole, it pushes water out, backwards. The water moving out the back of the boat pushes it forward, just as hot gases coming out of the bottom of a rocket push it upwards.

Download our boat templates and info sheet and race some boats yourself. Try using different liquids as ‘fuel’ to see which makes the boat travel furthest and fastest.

This series of ExpeRimental is supported by the Royal Society of Chemistry.

ExpeRimental, brought to you by the Royal Institution of Great Britain, is a series of free short films that make it fun, easy and cheap to do science at home with children aged 4 to 10. Our films give you lots of ideas for kids’ activities that will help you explore the world around you, question and experiment together. We’ll show you how to do the activity and how to make sure adults and children get the most out of it. Why not have a go and then tell us what you think on our Facebook page?

Here’s what you’ll need for this experiment:
Washing up liquid
Dried oregano or chilli flakes or coarsely ground black pepper
Shallow dish / plate with a lip
Range of household liquids, for example: vinegar, milk, cooking oil, liquid hand soap, shampoo, conditioner, soysauce
Ice cube tray
An empty juice carton or plastic milk bottle
Cotton buds
Baking tray

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  1. Not wanting to be a killjoy but this experiment was a massive let down. One dab of the cotton bud and the boats no longer move as the surface is already covered in soap. Think we'll make some scones instead 🙂

  2. congratulations. definitely is another way of looking at science. In my country is narrative and descriptive plans and curricula. greetings. social science teacher. professor of primary basic education

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