Toothpick Trick

You will need:

  • a clean dish
  • water
  • 6 flat wooden toothpicks or matches
  • washing up liquid

 

Try this

Dip one of your toothpicks in washing up liquid. Set it aside for now

Make sure your dish is clean and rinse it well with water. Fill it with water.

Place five soapless toothpicks in the shape of a pentagon onto the water’s surface. Overlap your toothpicks so that your pentagon stays together.

Dip a clean toothpick into the centre of this pentagon… and nothing happens.

Now take the toothpick that was dipped in the soap and dip the soapy end into the centre. What happens now?

 

Whats Happening?

Water molecules stick together. Think about when a bit of water falls on a table or a window, it stays together in a little droplet. The molecules on the surface of our dish are also sticking together and this causes surface tension. The toothpicks were reasonably flat so they could float on this layer without breaking the tension. However the soapy toothpick has soap molecules on it and these soap molecules break the surface tension of the water. This break has a ripple effect on the surface of the water. The surface tension originally holding the toothpicks breaks apart releasing the sticks from their pentagon shape.

 

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