- Two cups
- A piece of string, roughly 15cm long
- Food colouring
- Fill up one cup half way with water and drop in the piece of string, let it soak in the water for two minutes.
- Take it out of the cup, strain it a bit and tape one end to the inside of one cup and the other end to the inside of the other cup.
- Add some food colouring to the leftover water.
- Hold the cups as shown in the picture (do this above a tray) and start pouring the coloured water slowly down the string to the other cup. Hopefully the water will go down the string and not onto the table.
The science bit:
- Water is cohesive which means it sticks to itself, i.e. water attracts water. This means that when the first water molecule flows down the string, the other water molecules start to follow it.
- Water is adhesive which means it attracts to other substances, here the string. As long as you pour slowly enough, the adhesive power of the water sticking to the string will be stronger than the force of gravity so the water won’t fall off the string and will travel all the way down to the second cup.
- Wht did you think of this water on a string experiment? Why don’t you try the experiment again with different liquids or a longer string? Does a more viscous liquid such as golden syrup work better or worse?