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What Is Surface Tension | Cool Science Experiment

Surface tension is the glue that binds water into a cohesive sphere and the force that makes water bead up on a surface.

It is one of the amazing properties of water.

Surface tension in water is created by the attractive forces between the water molecules

It can be broken up.

In this experiment, we will break up the surface tension in water using a common household item.

We’ll make it easier to see by sprinkling peppers into the water.

finger dipped into a dish of peppers and the peppers disperse

What Is Surface Tension

Prep Time: 10 minutes
Additional Time: 5 minutes
Total Time: 15 minutes

Here is an excellent experiment demonstrating how water surface tension works.

Materials

  • black pepper
  • a plate or bowl
  • water
  • liquid soap (I used liquid dish soap)

Tools

  • adult supervision

Instructions

  1. Fill the plate with a thin layer of water. Less than an inch deep is enough.
  2. Sprinkle pepper onto the water. Try to cover as much the surface as possible. (The more pepper, the more spectacular the effect!)
  3. Dip your finger into the liquid soap.
  4. Say "Abacadaba" and touch the pepper in the water.


This experiment is simply magical. It can definitely impress kids and spark their interest in STEM.

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Why

Did your magic spell just cause the pepper to immediately scatter and dart away from your finger towards the edge of the plate?

No, it’s not your magic spell. It’s water’s surface tension.

More precisely, it’s the soap breaking the surface tension that caused the reaction.

Surface tension exists in water because water molecules (the little pieces of water) tend to stick to one another (cohesion).

Water has high surface tension, which means the molecules are pulling each other on the surface very strongly.

The pulling is so strong that when you first sprinkle pepper onto the water, it sits on top of the water instead of sinking into it. 

When soap is added in the middle, it breaks the surface tension there but surface tension still exists in other parts of the water.

Therefore, water molecules close to your finger are pulled away by molecules farther away carrying the pepper along with them.

And because the surface tension is broken in the middle, some pepper sink to the bottom (because pepper has a higher density than water).

References And More Experiments

Check out more experiments ideas using water.

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