water-surface-tension

Water has a property we see everyday called water surface tension.

If you have ever watched bugs appear to skate on top of the surface of the water, they are using water surface tension to move across the water without it sinking. We tried this water tension experiment to help us understand why.

Materials needed:

  • small paperclips
  • small bowl or cups
  • water
  • liquid soap

 

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Water cohesion that pulls the water molecules together. We can see examples of water cohesion in nature. If you pour water over a car windshield it groups together to form drops and streams of water. Water joins together to form streams, rivers and oceans.

In this experiment we know that paperclips are heavier than water as they sink to the bottom. When they are carefully placed at the water surface, however it floats. There is an added force at the surface of the water that is not present under the surface of the water. It is called surface tension.

Since all of the water is below the surface and there is no water above it there is internal pressure created in the water at the surface. This acts like a skin that helps the paperclip float on the water surface.

 

What happened when the soap was added? Why did the paperclip suddenly sink? Simple. The soap reduces the cohesion force in the water resulting in removing the “skin” from the water surface.