Surface Tension : Viscosity and Poiseuille flow Video Lecture - JEE

surface tension observe the zoom needle
placed on the surface of water and an
insect walking on the surface of water
we observe that the sealing needle which
is denser than water floats on it and
the insect is able to walk on the
surface of water how is this possible
this is because free surface of water
which is at rest behaves like a
stretched elastic membrane supporting
the needle and the insect this property
of liquid is known as surface tension
the surface tension can be defined as
the property of matter by virtue of
which the free surface of the liquid
address behaves like a stretched elastic
membrane having contracted tendency
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let us now study this property of liquid
in terms of molecular force of
attraction consider three molecules a b
and c of a liquid the dotted circle
drawn around each molecule represents
the sphere or faction of each molecule
observe that the sphere of influence of
the molecule a is completely inside the
liquid it is attracted equally in all
directions by the other molecules there
is no resultant force acting on the
molecule a the molecule B that is closer
to a also does not experience resultant
force what about molecules C a part of
the sphere of action is above the liquid
surface the molecule C experiences a
resultant downward force now consider
the molecule D that lies on the liquid
surface this molecule has its sphere of
action
exactly half outside the liquid and half
inside the liquid thus the molecule D
experiences a downward attractive force
due to this downward attractive force
the molecules on the surface experience
a tension called surface tension click
on the link provided to view some more
illustrations
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