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Soap and Surface Tension

Soap and Surface Tension

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Science Fair Project Description

Ever see water striders (A type of insect) travel across the surface of pond water? Have you ever seen what happens when you add oil to water? Both examples demonstrate the concept of surface tension, a condition where the molecules of a substance are so closely attracted to each other that they form a barrier. The clinging water molecules form a barrier strong enough to support both the water skater and the oil. In this science fair project, you will find out how soap affects water tension.


Water molecules consist of one hydrogen atom and two oxygen atoms. Hydrogen has a positive charge, while oxygen has a negative charge. Since opposite charges attract, the hydrogen atom of one water molecule will attract the oxygen atoms of another water molecule, while the two oxygen atoms of the molecule will attract the hydrogen atom of yet another water molecule. With all the water molecules behaving this way, the "network" of connected water molecules create a barrier to non-water molecules. Soap has the ability to break these connections, allowing water to become permeable to the molecular structure of other objects, such as oil. In this science fair project, the soap allowed the oil and water to mix. This is why soap is used on oil spills and why we use soap when we wash ourselves, dishes, or clothes.

Scientific Terms

Surface tension, Soap


  • A large drinking glass, jar, or beaker
  • Water
  • Vegetable oil
  • Liquid soap


  1. Fill three quarters of the jar with water.

  2. Pour a small amount of vegetable oil into the jar, just enough to raise the fluid level of the jar but allowing enough space to prevent the jar from over flowing.

  3. Observe how the oil and water remain separate from each other.

  4. Add a small amount of liquid soap, just enough to cover the liquid surface.

  5. Mix the jar and observe what happens to the oil and water.

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