Steps for the experiment:
Pour water on a dish.
Add pepper into the dish.
Put some detergent on the tip of one finger.
Touch center of the water with the finger (that has detergent on it) and observe what happens.
Result:
The pepper spreads away from the spot touched by the finger.
Why did this happen?
The intermolecular attraction in water molecules is very strong, which causes its surface tension to act strongly as well. However, when detergent, which is a surfactant (comes from the word 'surface active reagent'), is added, it reduces the surface tension. Because lighter substances move faster in water than heavier ones, the phenomenon can be observed better with such substances (such as pepper, which I used).
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