Viscosity → It is defined as internal resistance to flow of liquids

All parts of liquid do not move with the same velocity through tube : from centre towards the walls of tube, the velocity decreases.

Viscosity is also defined as the force of fraction which one part of liquid offers to another part of liquid.

The force of fraction ‘f’ between two layers each having area ‘A’ square cm. separated by distance dx cm having velocity difference ‘dv’ then.

f ∝ A (dv/dx) or f = η A (dv/dx)

Where η → coefficient of viscosity

(dv/dx) → velocity gradient

Coefficient of viscosity is defined as force of fraction (in dynes) required to maintain a velocity difference of 1 cm/sec bet. two parallel layers 1 cm apart and each having area of 1 square cm.

Units of viscosity → η = (dx/A.dv) = (dynes * cm/cm² * cm * sec) = dynes cm^-2 sec^-1 = 1 poise

 or       η = g cm^-1 s^-1 = 1 poise

Higher the intermolecular force of attraction, increases is the viscosity.

With the increase of temperature, viscosity decreases