Experiment for kids at home – Use pepper to observe surface tension


In this easy experiment for kids at home, we will talk about surface tension. What is surface tension? It is a force that exists at the point of contact between two elements of a different medium. We’ll see how to demonstrate this tension and how to break it!

Equipmentfor this experiment for kids at home:

  • A plate
  • Water
  • Pepper
  • A toothpick
  • Washing-up liquid

1. Fill the plate with water. Sprinkle pepper evenly over it.

2. Dip the toothpick in the water at the centre of the plate. There is no apparent reaction.

3. Apply a little washing-up liquid to the toothpick. Dip it back into the water. The surface tension on the surface of the water is broken.

Explanation of this experiment for kids at home:

Water molecules are attracted to each other by van der Waals force. Imagine that the molecules are all holding hands and that they are pulling against each other in order to become closer. The surface molecules are therefore drawn downwards and sideways as they are connected with the other molecules. This force is the surface tension. It creates a thin skin of resistance. When adding pepper, it is deposited on top of the skin.

By dipping the toothpick coated with washing-up liquid, the resistance between the molecules is broken. Imagine you are piercing a balloon. The water molecules that are far away from the toothpick have more surface force. They therefore attract the other molecules more easily, which is visible thanks to the pepper.

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