Question

The SI unit of kinematic viscosity is
1. m/s
2. m²/s
3. m³/s
4. Kinematic viscosity is a dimensionless quantity.

Answer 1

Correct Answer - Option 2 : m²/s

The correct answer is option 2) i.e. m²/s.

CONCEPT:

• Kinematic Viscosity: The measure of a fluid's internal resistance to flow under the influence of gravitational forces is called kinematic viscosity.
  • It is the ratio of Dynamic Viscosity to the fluid's mass density.
• Dynamic Viscosity: It is the measure of the internal resistance developed in the fluid against the force that can cause the liquid to flow.
  • Its SI unit is pascal-seconds.
• Mass Density: It is the ratio of the mass of fluid to the volume of the fluid. Its SI unit is kg/m³.

EXPLANATION:

• Kinematic Viscosity is the ratio of dynamic viscosity to mass density.

Hence, the unit of kinematic viscosity will be = \(\frac{N/m^{2}-s}{kg/m^3} = \frac{kg\times m/s^{2}\times s}{m^{2}\times kg/m^{3}}=\frac{m^{2}}{s}\)

• m/s is the SI unit of speed or velocity of the flowing fluid.
• m³/s is the SI unit of rate of flow of fluid or also called discharge rate of the fluid.

• The kinematic viscosity is often expressed in the C.G.S system as Poise.
• 1 poise = 10^-4 m²/s.
• The difference between kinematic and dynamic viscosity is that dynamic viscosity is the measure of force needed to make the fluid flow at a certain rate whereas, kinematic viscosity is the measure of the rate at which the fluid is flowing under the influence of a certain force.