Dynamic Viscosity vs Kinematic Viscosity | Difference between Dynamic Viscosity and Kinematic Viscosity

This page compares Dynamic Viscosity vs Kinematic Viscosity and mentions difference between Dynamic Viscosity and Kinematic Viscosity.

• Viscosity: It is the inherent property of fluid which offers resistance to the flow.
• Viscosity of liquids decreases with increase in the temperature.
• Viscosity of gases increases with increase in the temperature.
• Viscosity can be defined as measurement of fluid internal resistance to flow at specified temperature.
• There are two methods to measure viscosity of a fluid viz. dynamic viscosity and kinematic viscosity.

Dynamic Viscosity (μ)

• It is defined as fluid's resistance to flow.
• It can also be defined as fluid's resistance to deform when subjected to force.
• It can be expressed as follows.
➤ Dynamic Viscosity (μ) = Shear Stress/Velocity Gradient
Si unit of dynamic viscosity is Nsec/m²
The commonly used unit is Poise or Centipoise (i.e. cP) .
➤1 cP = mPa.s
• Water at 20 degreeC has a viscosity of 1.0020 cP or 0.001002 kg/(m.s).

Kinematic Viscosity (v)

• It is defined as fluid's resistance to flow.
• It is usually measured by noting down the time taken for fluid sample to travel through an orifice in a capillary under force of gravity.
• Time taken is being noted and converted to kinematic viscosity.
• The cgs physical unit for kinematic viscosity if stokes(St). It can also be reported in Centistoke (cSt) or m²/s.
• 1 St = 1 cm².s^-1 = 10^-4 m². s^-1
• 1 cSt = 1 mm²/s.
• Water at 20 degree C has kinematic viscosity of about 1 cSt.
• The kinematic viscosity is referred as diffisivity of momentum.

• Both Dynamic viscosity and Kinematic viscosity are interchangeable using following formula.
➤Kinematic Viscosity = Dynamic Viscosity/Fluid density
➤1 SI unit of kinematic viscosity = 10⁴ stroke

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