Rufus and the racers

Comedian Rufus Hound and his son Alby make soap powered boats and learn how soap affects the way water molecules hold onto each other.

Aims

Make boats that race across water, powered by soap.

ExpeRiment with different liquids to see if they produce the same effect.

Learn how soap affects the way water molecules hold onto each other.

  • Media

    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

About this activity

Comedian Rufus Hound and his son Alby make soap powered boats and learn how soap affects the way water molecules hold onto each other.

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.

Don't forget to download the badges and certificates for afterwards! Share photos and videos of your experiments on our Facebook page.

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