Consider a molecule in the interior of liquid present in a container, it is attracted from all sides by other molecules so no net force is on it.
Now consider a molecule on the surface of a liquid. It is attracted from all sides except the upper side so it experiences a net downward force due to which the liquid surface stretches. This is surface tension.
Surface tension is defined as
βStretching of a liquid surface due to net downward forceβ
OR
βThe force acting perpendicularly downward at the right angle to the unit length of liquid surfaceβ
OR
βThe work done in increasing unit area of liquid surfaceβ
Factors affecting Surface Tension:
1. Intermolecular forces:
Stronger are the intermolecular forces high will be the surface tension and vice versa. e.g.
Surface tension order for water, alcohol (spirit), mercury & ether is
Hg > H2O > C2H5OH > C2H5-O-C2H5
Ether has London forces; mercury has metallic bonding while the other two have Hydrogen bonding. London forces are weaker so ether has low surface tension. Water and alcohol have hydrogen bonding so their surface tension is higher than ether. Hydrogen bonding of water is stronger than that of alcohol so the surface tension of water is higher than alcohol. Mercury has metallic bondings which are stronger than hydrogen bonding so the surface tension of mercury is still higher.
2. Temperature:
Higher is the temperature weak will be the forces and thus low will be the surface tension. e.g. surface tension of hot water is lower than that of cold water.
3. Soap or detergent:
The presence of soap or detergent decreases the surface tension of water because forces among water molecules become weaker.
4. Salt:
The presence of salt increases the surface tension of water because salt ions attract water molecules with greater force. e.g. surface tension of seawater is higher than that of fresh water.
Surface Tension Examples
Small insects called “water striders” are able to walk on water because it takes far less of their weight to pierce the water’s surface. There are other instances of surface tension in nature that are similar to this. Below are a few examples:
- insects moving through water
- floating a needle over the water’s surface
- Materials for rainproof tents where water’s surface tension will cause the pores to be bridged
medical examination for jaundice - disinfectants for surface tension (disinfectants are solutions of low surface tension).
- washing clothing with soaps and detergents that reduce the water’s surface tension
- using cold water to wash
- Water bubbles form in the form of rounded bubbles where the water’s surface tension acts as the wall tension.
The shape of liquid droplets is also a result of this phenomenon.
Measurement of Surface Tension:
Units of Surface Tension:
S.I. Units β N/m, J/m2
CGS System β dyne/cm, erg/cm2
How to Calculate Surface Tension?
Methods to Calculate Surface tension:
There are three methods of measurement of surface tension
1. Torsion balance method
2. Capillary rise method
3. Drop method using Stalagmometer:
In this method, relative surface tension is measured. For this purpose number of drops of reference and test liquid are counted for a volume of liquids present between two marks a & b on the stalagmometer.

Water is usually chosen as a reference liquid.
Its surface tension at 293K is 7.275 x 10-2 N/m or 72.75 dyne/cm
Cohesive and Adhesive Forces:
The forces of attraction among liquid molecules themselves are called cohesive forces. The forces of attraction between liquid molecules and the wall of the container are called adhesive forces.
The liquids that have adhesive forces stronger than cohesive forces form concave meniscus and they are wetting liquids e.g. water.
The liquids that have cohesive forces stronger than adhesive forces, form convex meniscus and they are non-wetting liquids e.g. mercury.
The shape of the liquid surface is called the meniscus.
Capillary Action:
The rise of liquid in a capillary tube is called capillary action.
It is due to strong adhesive forces between the liquid and the wall of the capillary. e.g. spreading ink or water on blotting paper, absorption of water by cotton, water absorbed by roots from the soil is supplied to leaves through the xylem, supply of oil to a flame by wicks, all these are due to capillary action. These materials are porous and their pores act as capillaries.
The tubes of narrower bores show more height. Actually same volume of liquid rises through capillary tubes, so the less the area of the cross-section of the tube more will be the height gained by liquid as Volume = Area x Height.
Frequently Asked Questions β FAQs
Why is a raindrop spherical?
cohesion forces between liquid molecules and the liquid’s surface tension.
When a soap bubble gets charged, what happens?
A soap bubble enlarges after being charged.
What is the surface tension dimensional formula?
What does boiling water’s surface tension look like?
At the boiling point, water has no surface tension.
What factors are responsible for the development of surface tension?
Cohesive and adhesive forces are responsible for the development of surface tension.
awe-inspiring site thank you so much for placard unconvincing cognitive content
thank you for the amazing post
thank you so much for this awe-inspiring web site me and my family admired this contentedness and penetration
thank you so much for this awesome website me and my family admired this self-complacent and sixth sense
thank you so much for this awful site me and my household best-loved this contentedness and sixth sense
thank you so much for this awe-inspiring web site me and my kin preferent this content and insight
thank you so much for this awful web site me and my class precious this message and insight
thank you so much for this awful site me and my sept precious this message and penetration
thank you so much for this astonishing internet site me and my household best-loved this depicted object and sixth sense
thank you so much for this amazing internet site me and my family favored this self-complacent and insight
thank you so much for this amazing website me and my household best-loved this self-complacent and sixth sense
thank you so much for this awe-inspiring site me and my phratr admired this content and penetration
thank you so much for this amazing website me and my class precious this depicted object and brainstorm
thank you so much for this amazing internet site me and my family favored this contentedness and perceptiveness
thank you so much for this amazing website me and my family best-loved this contentedness and perceptivity
thank you so much for this astonishing site me and my sept preferent this depicted object and perceptiveness
thank you so much for this astonishing web site me and my class favored this message and perceptiveness
thank you so much for this amazing website me and my class best-loved this depicted object and penetration
π thank you so much for this impressive internet site me and my kin admired this contentedness and perceptivity
π thank you so much for this amazing web site me and my class favored this contentedness and insight
π thank you so much for this amazing web site me and my household preferent this depicted object and penetration
π thank you so much for this awesome site me and my kin best-loved this content and perceptivity
π thank you so much for this awful site me and my kin preferent this self-complacent and perceptiveness
π thank you so much for this astonishing website me and my family favored this content and insight
π thank you so much for this awesome site me and my family preferent this contentedness and sixth sense
π thank you so much for this awful website me and my sept loved this content and penetration
π thank you so much for this impressive internet site me and my sept preferent this satisfied and perceptiveness
π thank you so much for this astonishing site me and my class preferent this contentedness and penetration
π thank you so much for this awe-inspiring web site me and my sept admired this contentedness and sixth sense
π thank you so much for this awe-inspiring website me and my sept precious this depicted object and penetration
π thank you so much for this amazing internet site me and my family best-loved this message and perceptiveness
π thank you so much for this awesome web site me and my phratr favored this self-complacent and perceptiveness
π thank you so much for this impressive web site me and my kin best-loved this satisfied and brainstorm
π thank you so much for this awful web site me and my class precious this self-complacent and brainstorm
π thank you so much for this astonishing site me and my family favored this depicted object and sixth sense
π thank you so much for this awesome internet site me and my sept loved this message and sixth sense
π thank you so much for this impressive website me and my phratr best-loved this contentedness and brainstorm
π thank you so much for this awe-inspiring website me and my family precious this content and insight
π thank you so much for this amazing site me and my kin precious this self-complacent and penetration
π thank you so much for this amazing internet site me and my phratr preferent this contentedness and brainstorm
π thank you so much for this astonishing web site me and my kin admired this contentedness and insight
π thank you so much for this awesome internet site me and my household favored this message and perceptivity
π thank you so much for this awesome web site me and my family precious this satisfied and perceptivity
thank you so much for this astonishing web site me and my kin favored this satisfied and penetration
Pingback: What is a Simple definition of Viscosity? - Best Online Free Chemistry Learning
Pingback: What is vapour pressure easy definition? - Best Online Free Chemistry Learning
Pingback: What is a simple definition of evaporation? - Best Online Free Chemistry Learning