Home > Funny, Science, Sport, water > Water – Part II (Understanding Surface Tension)

Water – Part II (Understanding Surface Tension)

Remember throwing stones in stagnant water, see it bounce off the surface?? Why do ships float while a screw made out of the same metal, sinks?? And what would happen if u take a dive flat chested on water?

The answer to the all these questions lies in a property called ‘Surface Tension’

Surface tension is the force exerted by water molecules that lie on the surface of the water. On a more scientific note, Surface tension is caused by the attraction between the liquid’s molecules by various intermolecular forces. The molecules under the surface of the water attract and get attracted making the net force under water,zero. However, At the surface of the Liquid, The molecules are pulled by molecules that lie below them and to the side of them. The force of attraction is absent above them as they are not attracted by molecules in the neighboring system (Vacuum, air or another liquid) leaving the forces unapplied in the upward direction. Thus the upward force applied by water molecules that lie on the surface of water is ‘Surface tension’.

Now, When u throw a stone with its flatter side hitting the water first (assuming u used some power to give it speed) the stone will probably bounce off. This happens because the force applied by the stone is probably less than force applied due to surface tension water. The stone eventually sinks to the bottom. With speed comes lightness or reduced weight(weight will be distributed in direction other than the downward direction, the direction in which wight is measured) Using formulas,[ Force= (w*a)/g; where w= weight of the object(on earth), a is the acceleration/deceleration on the object and g is the gravitational force.]

Did u know:

  • U can push a car loaded with 2 people only using the pressure of water?? About 12 atmospheric pressure of water leaves the nozzle of a fire engine pump. This pressure is enough to push a car with 2 people inside over some distance.
  • Some industrial uses of water includes, high power jet cutters where water at very high pressure is used to cut steel.

What would happen if, you dive flat on water??

A diver takes a dive at the olympics

Lots of pain!! Broken bones is probably what u will end up with. The higher the diving platform the greater the pain. Similar to our stone throwing experience, the more the part of body exposed to water the more the surface tension the body will have to experience. This is a reason why divers use a specific technique. By closing two arms together, The divers penetrate the water surface, separating the water molecules, breaking down Surface tension. Air is blown into the pool to break down surface tension, during diving competitions. The air molecules separate the water molecules and reduce surface tension! This is done to prevent injuries to the diver if things go wrong!

These examples should have given u an idea of why things float. To put it in a simpler form, If the force applied by the object is more than the surface tension, the object will sink. Object float if the force applied is more than the force applied by water molecules. The ships are designed to distribute all the weight evenly on the base. Thereby canceling the amount of surface tension per sq. inch of water to that of the ship. While pins made of the same metal experience lower surface tension because of their small surface area, making them sink.

[Weight is the amount of force applied, using complex formula, the actual force applied can be calculated]

So should it be possible to walk on water like the illusionists do it? To put the answer in word: No. However, similar to the stone throwing experience, if we travel if we travel over the surface of the water with good speed, staying afloat could be possible. Possible Example: Water Skiing. To achieve such skiing effect the skier needs to travel at a speed of minimum 56Kms an hour. It reduces the force that u exert on water giving it a floating effect.

Pressure of water can be utilized in many other ways, Hydroelectricity plants use water at high pressure to run turbines for generating electricity.

Water has many uses, be it industrial as steam to generate to generate electricity,as high power water jets for Fire engines and machines, As a solvent to various industrial chemicals to neutralize their effects, as a coolant in most industrial plants,or for domestic needs like Drinking, Washing, Cooking etc. But are we actually taking care of this most important thing in the world??

Recent studies show that If we consume or waste water at a similar rate, We would deplete all our fresh water resources by 2025. People around the world are looking at ways to minimize water usage,U can read more on water preservation and conservation on my blog – ***Save Water, Save Ourselves***

I’m doing my bit to help save the world, If not for ‘US’ saving it together, Life is coming to an end!

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  1. Nitu
    October 8, 2010 at 12:16 pm

    Thanks for the surface tension concept but I am wondered to see a post based on some scientific topic. However that was crisp. But you should have used the word “COHESIVE FORCES” which is the exact reason for attraction.

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