Water Surface Tension Experiment

Sprinkle one teaspoon of black pepper over the bowl of water.

The pepper is able to float on the surface because water molecules like to cling to one another. They arrange themselves in a way that creates surface tension on the top of the water. This tension keeps the pepper floating on top instead of sinking to the bottom of the bowl.

When a tiny drop of washing-up liquid (soap) is added to the bowl the pepper darts away from the liquid because soaps are designed to break down the surface tension of water. This helps make them good cleaning tools.

The water molecules, however, want to stick together and maintain that tension, so they move away from the soap, carrying the pepper.