4 March 2017

What is viscosity

Viscosity definition :

Viscosity is the property of a fluid which determines its resistance to shearing stresses.

Cause of Viscosity: 

It is due to cohesion and molecular momentum exchange between fluid layers.

Newton’s Law of Viscosity: 

It states that the shear stress (τ) on a fluid element layer is directly proportional to the rate of shear strain.

T = µ (du/dy)

Where µ = Coefficient of dynamic viscosity 

Units of Viscosity :

S.I Units : Pa.s or N.s/m2
C.G.S Unit of viscosity is Poise = dyne-sec/cm2
One Poise = 0.1 Pa.s
1/100 Poise is called centipoises.
Dynamic viscosity of water at 20 0C is approx= 1 cP

Kinematic Viscosity :

Kinematic viscosity is the ratio between the dynamic viscosity and density of the fluid.
It is denoted by ν.
ν = dynamic viscosity / density 

Units of Kinematic Viscosity :

S.I units: m2/s
C.G.S units: stoke = cm2/sec
One stoke = 10-4 m2/s

Viscosity and density are two same terms but there is a difference between them. Let we check it out the difference between viscosity and density.