Viscous Force:
The force which opposes the relative motion between different layers of liquid
or gases is called viscous force.
Viscosity:
Viscosity is the property of a liquid by virtue of which it opposes the
relative motion between its different layers.
Viscosity is the property of liquids and gases both.
The viscosity of a liquid is due to cohesive force between
its molecules.
The viscosity of a gas is due to diffusion of its molecules
from one layer to other layer.
Viscosity of gases is much less than that of liquids. There
is no viscosity in solids.
Viscosity of an ideal fluid is zero.
With rise in temperature, viscosity of liquids decreases and
that for gases increases.
Viscosity of a fluid is measured by its coefficient of
viscosity. Its SI unit is decapoise (kg/ ms) or Pascal second. It is generally
denoted by ŋ.
Terminal Velocity:
When a body falls in a viscous medium, its velocity first increases and finally
becomes constant. This constant velocity is called Terminal velocity.
In this situation, the weight of the body is equal to the
sum of viscous force and force of buoyancy i.e. the net force on the body is
zero.
Terminal velocity of a spherical body falling in a viscous
medium is proportional to the square of radius of the body.
