- 5 toothpicks
- A small plate
- Water in a small bowl
- Food colouring
- A pipette or eye-dropper
What to do
- Gather your materials on a flat surface.
- Bend all 5 toothpicks halfway so that they are bent into a V. Don’t break them right in half – they still need to be connected. If you do break them, try again with new toothpicks.
- Arrange the bent toothpicks on the plate like in the picture, without letting the ends touch.
- Add 1 or 2 drops of food colouring to the water in the bowl.
- Add 5 drops of coloured water to the centre of the toothpicks using the pipette. Make sure the drops of water touch the bent corners of all toothpicks.
- Watch the toothpicks. You may need to add a couple more drops of coloured water.
Questions to ask
Does this experiment work with things that aren’t wood? Try bending some plastic straws and repeat the experiment.
Do you have to use water? Try dropping oil onto the toothpicks.
The broken wood of the toothpicks absorbs the water they are sitting in by capillary action. As the water is drawn into the toothpick, the wood expands. The expanding wood on the inside of the V pushes against itself, which makes the toothpick straighten out. As the toothpicks push out, they form the star shape.
To learn more about capillary action, see the Walking Water activity.