Surface tension is the property of surface of liquids because of which surface behaves like a stretched elastic membrane.
Surface tension can be defined as the force acting per unit length normal to the surface of the liquid.This can be explained based on molecular theory. This develops a tension like force on the surface and hence it is called surface tension.
Liquids have no definite shape but have a definite volume, they acquire a free surface when poured
in a container. These surfaces possess some additional energy. This phenomenon is known as surface tension and it is concerned with only liquid as gases do not have free surfaces.
A liquid stays together because of attraction between molecules. Consider a molecule well inside a liquid. The intermolecular distances are such that it is attracted to all the surrounding molecules [figure a]. This attraction results in a negative potential energy for the molecule, which depends on the number and distribution of molecules around the chosen one.
But the average potential energy of all the molecules is the same. This is supported by the fact that to take a collection of such molecules (the liquid) and to disperse them far away from each other in order to evaporate or vaporize, the heat of evaporation required is quite large.
Let us consider a molecule near the surface figure b. Only lower half side of it is surrounded by liquid molecules. There is some negative potential energy due to these, but obviously it is less than that of a molecule in bulk, i.e., the one fully inside. Approximately it is half of the latter. Thus, molecules on a liquid surface have some extra energy in comparison to molecules in the interior. A liquid thus tends to have the least surface area which external conditions permit. Increasing surface area requires energy.
Since a liquid consists of molecules moving about, there cannot be a perfectly sharp surface. The density of the liquid molecules drops rapidly to zero around z = 0 as we move along the direction indicated figure c in a distance of the order of a few molecular sizes.
Thus molecules on the surface of liquid experience maximum downward force and hence the surface behaves like a stretched membrane.This property is called surface tension.
Other properties of Fluids :
Viscosity
Dynamic lift
Venturi meter
Torricelli's theorem
Blood flow and heart attack
Stream line flow
What is pressure ?
Pressure variation with depth
Pascal's Law
Surface tension can be defined as the force acting per unit length normal to the surface of the liquid.This can be explained based on molecular theory. This develops a tension like force on the surface and hence it is called surface tension.
Liquids have no definite shape but have a definite volume, they acquire a free surface when poured
in a container. These surfaces possess some additional energy. This phenomenon is known as surface tension and it is concerned with only liquid as gases do not have free surfaces.
A liquid stays together because of attraction between molecules. Consider a molecule well inside a liquid. The intermolecular distances are such that it is attracted to all the surrounding molecules [figure a]. This attraction results in a negative potential energy for the molecule, which depends on the number and distribution of molecules around the chosen one.
But the average potential energy of all the molecules is the same. This is supported by the fact that to take a collection of such molecules (the liquid) and to disperse them far away from each other in order to evaporate or vaporize, the heat of evaporation required is quite large.
Let us consider a molecule near the surface figure b. Only lower half side of it is surrounded by liquid molecules. There is some negative potential energy due to these, but obviously it is less than that of a molecule in bulk, i.e., the one fully inside. Approximately it is half of the latter. Thus, molecules on a liquid surface have some extra energy in comparison to molecules in the interior. A liquid thus tends to have the least surface area which external conditions permit. Increasing surface area requires energy.
Since a liquid consists of molecules moving about, there cannot be a perfectly sharp surface. The density of the liquid molecules drops rapidly to zero around z = 0 as we move along the direction indicated figure c in a distance of the order of a few molecular sizes.
Thus molecules on the surface of liquid experience maximum downward force and hence the surface behaves like a stretched membrane.This property is called surface tension.Other properties of Fluids :
Viscosity
Dynamic lift
Venturi meter
Torricelli's theorem
Blood flow and heart attack
Stream line flow
What is pressure ?
Pressure variation with depth
Pascal's Law
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