A thin stream of water can be easily bent using a plastic comb or ruler which was previously rubbed with wool. This demonstrates the attractive forces between unlike charges.
- Plastic ruler
- Water from a tap
- Turn on the faucet for the thinnest stream of water with a consistent flow.
- Rub the plastic ruler with the wool.
- Place the part of the ruler which was rubbed near the stream of water without touching.
Water molecules are polar in nature, which means that one side (where the oxygen atoms are) is more negative while another side (where the hydrogen atom is) is more positive. When wool is rubbed with plastic, it deposits electrons on the ruler.
The electrons will remain on the plastic as it is a poor conductor of electricity. When placed near the stream of water, the water molecules reorientate themselves such that the positive pole of each molecule is now nearer to the ruler than the negative pole.
The resulting attractive forces are stronger than the repulsive forces as the forces between charges decrease when the distance apart increases.