Materials:
1. A small shallow bowl
2. Water
3. Cocktail stick or toothpick
4. Washing-up liquid
5. Ground pepper
Instruction:
1. Half-fill bowl with water.
2. Sprinkle a thin layer of ground pepper on the surface of the water.
3. Dip a cocktail stick in washing-up liquid then touch the middle of the water with the stick's tip. See what happens?
Explanation:
Washing-up liquid reduces surface tension. This allows the particles of water at the surface to spread out, starting where the washing-up liquid was added. As they spread they push the grains of pepper to the side.
