Surface tension is the property of any liquid that causes it to resist the external force.
Surface Tension is responsible for many properties of liquid.
Cause of surface tension: It is caused by the cohesive force amongst the same molecules of liquid.
In bulk, liquid molecules are surrounded by other molecules and are equally attracted in all directions, but the molecules on the surface are not stable as they are not equally attracted by other molecules and they are drawn inwards. As a result liquid tends to contract and acquire minimum surface area to equilibrate.
Example from day today life: Liquid drop and Bubbles are spherical, this because the surface tension is minimum spherical shape.
More examples of surface tension:
Dew Drops are spherical, Water dripping out of tap is also spherical, beading of water on waxy surface (wax changes the surface properties), mercury in thermometer (mercury in thermometer does not stick to it’s walls due to surface tension), separation of oil and water occurs due to difference in surface tensions of two liquids.
Surface Tension is represented by Gamma and is defined as force per unit length.
The force acting is parallel to the surface but perpendicular to the line.
SI Unit: Newton per meter (N/m) cgs Unit: dyne per centimeter (d/cm).