Foil Boat

Hopefully you won’t need 78 attempts to get your foil boat moving!

What you need

  • Kitchen foil and sharp scissors. Try not to use cheap kitchen foil — the thicker it is, the better.
  • Washing up liquid.
  • Washing up bowl filled with clean water.

What you do

  1. Cut your foil boat to the approximate design shown in the SciCast film.
    The dimensions aren’t vital, but smaller may be better, as it’s best if the foil is as smooth as possible — bigger pieces may be more affected by wrinkles. The foil needs to be made as smooth as possible, almost ironed, because you don’t want the washing-up liquid molecules to be able to get under the foil boat.

  2. You should have a cutaway shape at the back (stern) of the boat — this is the place into which you’ll put a drop or two of washing up liquid.

  3. There’s no harm in making the front (bow) pointy, for streamlining.

  4. Gently place the foil boat on the water in one corner of the washing-up bowl.

  5. Add your drop(s) of washing-up liquid to the water surface in the cut-out.

What’s going on?

The boat should float on the water due to surface tension.

Soap molecules will tend to spread over the surface of the water, but due to the foil of the boat being in the way, they can only go ‘backwards’ initially. The boat is shoved forwards by the reaction to this movement, akin to the recoil of a gun when it fires a bullet.

If you want to repeat this, you may need to empty out the water and start again with fresh — once the water has a detergent layer all over it, the motion stops.