Experiment: A paperclip is afloat on a cup of water. Then a Q-Tip containing liquid soap is repeatedly dipped into the cup, avoiding the paperclip.
Observation: After multiple dips, the paperclip no longer floats on the surface of the cup and sinks to the bottom
- The water molecules at the surface of the cup are strongly attracted to each other due to their inherent polarity (water molecules have two sides holding opposite charges – a positive electric charge on the hydrogen atoms’ side and a negative electric charge on the oxygen atom’s end.) This attraction is called cohesion. If a large amount of force is applied to the molecules, cohesion will be decreased.
- Soap decreases the cohesion at the surface of the cup because every soap molecule has two sides – a grease-attracting side and a water-repellent one. The water-repellent aspect of soap exerts force on the water molecules, preventing them from forming bonds with each other, breaking the surface tension and sinking the paperclip in the process.