Surface Tension

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Surface Tension

• By Shardae

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What causes surface tension?

• Surface tension is caused by cohesion.
• cohesion is a force that causes the molecules of
  a substance to be attracted to one another.
• The molecules of a liquid that are below surface
  have similar molecules pulling on them from all
  directions.
• But only the molecules below and on their sides
  attract the molecules on the surface.
• These downward and sideways attraction of the
  molecules creates, a constant pull on the surface
  molecules, cause surface tension.

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Properties of surface tension

• Surface tension is a force that causes the
  surface of liquids to behave in certain ways.
• It causes a liquid to behave as a thin elastic
  film covering its surface.
• Surface tension also causes a liquid to rise in a
  thin tube when the tube is dipped in the liquid.
  This action is called capillarity action.

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Capillary action

• Capillary rise under residual acceleration.

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More properties

• Because of surface tension, drops of liquids take
  a spherical shape, which has the smallest
  possible surface area.
• For example, raindrops fall as spheres.

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Its all pressure

• Surface tension is typically measured in
  dynes/cm, the force in dynes required to break a
  surface film length of 1cm.
• Equivalently, it can be stated as surface energy
  in ergs per square centimeter.
• Water at 20 degrees Celsius has a surface tension
  of 72.8 dynes/cm, compared to 465 for mercury.

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• Surface tension also helps the cleaning of
  clothes. Hot water, soaps and detergents further
  lower the surface tension, so that it more
  readily soaks into pores and soiled areas.

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Walking on water

• The surface of water can support needles or razor
  blades if they are placed there carefully.
• Some insects walk on water - they dont put any
  more force on the waters surface than it can
  hold!
• Even spiders can do it!

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Bibliography

• http//www.funet.fi/pub/sci/bio/life/insecta/heter
  optera/gerromorpha/gerridae/aquarius/index.html
  (water strider photographs)
• http//www.colorado.edu/che/chen1000/3_5.pdf
  (detergent photograph)