To observe the phenomenon of cohesion in liquids by a simple experiment using water.
- Some water.
- A glass or cup.
- Some pins.
- Fill the glass or cup to the brim with water. Fill just enough so that it doesn’t overflow but a little more will surely make it overflow.
- Gently put on pin into the cup horizontally. Observe the increase in water level.
- Add more pins. You will see that the water level will increase and rise above the brim but still doesn’t overflow.
- Keep adding pins till finally one pin makes the water overflow.
All matter has a force called cohesion between its particles. Cohesion is the force of attraction between similar or like particles or molecules. It is strongest in solids, which is why solids remain in one shape always. It is weaker in liquids and the weakest in gases, which is why gases are completely free if not closed tightly in a container. In this experiment the water molecules stick to each other by cohesion and do not spill over even when you add a few pins. But after a number of pins, the force of cohesion in water is not strong enough to keep it from overflowing and at this point the water spills over the brim.