What is surface tension?

Liquids have a property that their free surface behaves like a stretched elastic membrane and has a natural tendency to contract, i.e , the free surface of a liquid tends to occupy a minimum surface area.
This property of liquids is called as surface tension.

Some experiments and examples related to Surface Tension-

1. Let us consider a frame. There is a closed loop thread attached with the frame loosely, so that it can change its shape. Now dip the frame in soap solution. Break the film created inside the loop. After breaking the film, it is observed that the thread occupies a shape  of a circle.
   
   REASON- The surface tension tends to make the surface area of the film as minimum as possible. And for a given length of thread, the surface area of circle is maximum, which eventually decreases the surface area of the film to minimum.
2. Brush in water-  When we put brush in water, the brush hair can be seen separately in water. But when we take out the brush out of the water, the water film between the hair gets contracted due to surface tension.
   
   So when we take out the brush out of water , the hair of the brush stick together.
3. The shape of rain drops is spherical. 
4. Insects can float on water surface.

Definition- The surface tension of a liquid is defined as the force per unit length in the plane of the liquid surface, acting normally on either side of an imaginary line drawn in that surface.

                                       T= F/L

where T is surface tension  F is force and L is length of the imaginary line.

Surface Energy- When the molecules from the interior of the liquid rise to the surface the surface area is increased.
Now this work is stored in the molecules in the form of potential energy.
The potential energy stored per unit area of the surface is called the surface energy.

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