SLO- Ledger Nr. 59. Magic finger- experiment


  • Pepper,
  • water,
  • plate and
  • dishwashing detergent


Description of the experiment:

Pour 200 ml of water onto a plate. Sprinkle the bottom with ground pepper. Put some detergent on the tip of your finger. Touch the surface of the water in the middle of the plate with your finger and observe what happens.


Explanation of the experiment:

Surface tension is the property of the surface of the liquid, which is formed by attractive forces between the molecules on the surface of the liquid, a kind of “birch”. Due to the superficial strength, the water forms droplets. When water is sprinkled with ground pepper, it is distributed over the surface of the water. When the detergent (on the finger) is added to the water, the surface tension of the water is reduced, causing the pepper to swim away from the detergent to the edge of the plate.

Detergents are important detergents that allow the removal of dirt (fat) in the water. The detergent molecule is polar at one end and therefore is hydrophilic (water attracts), and at the other end it is non-polar (long chain carbon and hydrogen atoms) and therefore hydrophobic (water is rejected by it).