Try this quick and easy science experiment to teach your children about surface tension. The best part? Clean up’s a sinch.
Materials
Bowl
Water
Ground black pepper
Liquid detergent
Directions
1. Fill the bowl with water
2. Shake in enough pepper to just cover the surface of the water
3. Dip your finger in the liquid soap
4. Now gently tap the top of the water and watch as the pepper immediately pulls to the outside of the bowl!
The Science
Water molecules are made up of two parts hydrogen and one part oxygen. The hydrogen atoms in each molecule have a slight negative charge that makes them stick equally to all of the other water molecules around them. When you have a bowl of water, the molecules at the top only stick to each other and the molecules below, which creates tension.
Detergent molecules have two ends. One end attaches to water and one repells water– it is this combination that helps the detergent to clean your dishes when it is mixed with water!
When the detergent touches the top layer of water, the water-repelling end of the molecules in the detergent immediately breaks the tension of the water’s surface. The pepper shows how the water is instantly repelled from the detergent.
