# What is surface tension ?

Surface tension property :

“It is defined as the force acting along the surface of a liquid at right angles to any line of 1 unit length.” It is numerically and dimensionally equal to surface energy. It has dimensions kg. $s^{-2}$ and n SI unit $Nm^{-1}$.

If we consider a molecule in the bulk of the liquid it experiences equal intermolecular forces in all directions. Hence there is no net force acting on it. But a molecule at the surface has intermolecular forces from inside only. Therefore there is a net attractive force on it towards the interior of the liquid. Due to this the surface area of the liquid tends to minimize. That is the molecules experience a downward force and have more energy than the molecules in the bulk.

Surface tension decreases with increase of temperature because of increase in K.E. of molecules and decrease in intermolecular forces.

Surface tension of liquids at $20^{\circ}&space;C$ in dynes/cm
Diethyl ether 16.9
Acetone 23.7
Carbon tetra chloride 26.9
Ethanol 22.3
Water 72.8