Surface Tension

What is Surface tension?

Have you ever noticed that when you fill a glass up to the brim with water, you can still add a few more drops till it spills out? Or have you ever broken a thermometer and observed how the fallen mercury behaves?


The picture above shows a certain amount of mercury spilled on the ground. But imagine if instead of mercury, the same amount of water was on the floor. It wouldn’t be just as curvy, would it?

This is where a property called surface tension comes into play. It is the tendency of liquids to acquire the least surface area possible. So what is surface tension? It is a phenomenon that occurs when the surface of a liquid is in contact with another phase (it can be a liquid as well). The surface of the liquid behaves like an elastic sheet.

Water at 100∘C has a surface tension value of 0.059 N/m and mercury has a surface tension value of 0.47 N/m.

If there is a small leaf or a paper clip placed on the surface of a glass of water, what causes it to float over it? The downward force of the body is balanced by the surface tension.

Surface Tension Formula:

It is expressed by the formula:



F is the force per unit length

L is the length in which force act

T is the surface tension of the liquid

Units of Surface Tension:

SI Unit N/m
CGS Unit dyn/cm

How to calculate Surface Tension:

Here is an example to calculate surface tension using the surface tension formula:

Question: Compute the surface tension of a given liquid whose dragging force is 7N and length in which the force acts is 2m?



F = 7N

L = 2m

According to the formula,

T=F/L ⇒T=7/2⇒T=3.5N/m

Stay tuned with Byju’s to learn more about surface tension, surface energy and much more.

Practise This Question

Hairs of shaving brush cling together when it is removed from water due to