Unit of Viscosity

Edited By Team Careers360 | Updated on Nov 12, 2024 11:51 PM IST

Viscosity Unit

The unit of viscosity or viscosity unit is Pascal seconds (Pa-s) or .

SI unit of viscosity

The SI unit of viscosity is given by Pascal seconds (Pa-s) or .

What is the viscosity unit?

Viscosity is defined as the property of a fluid which offers resistance to the movement of one layer of fluid over another adjacent layer of the fluid. When two layers of a fluid, a distance ‘dy’ apart, move one over the other at different velocities, let us say it ‘u’ and ‘u + du’. This viscosity together with the relative velocity causes a shear stress acting between the fluid layers. The top layer causes a shear stress on the adjacent lower layer while the lower layer causes a shear stress on the adjacent top layer. This shear stress is proportional to the rate of change of velocity with respect to ‘y’. It is denoted by symbol.

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Viscosity Unit
What is the viscosity unit?
Unit of viscosity
Types of Viscosity

Unit of Viscosity - Definition, Types, Unit, Example, FAQs

Mathematically,

…………………(i)

Also check-

Where (called mu), is the constant of proportionality and is known as the coefficient of dynamic viscosity or only viscosity. is the rate of shear strain or rate of shear deformation or velocity gradient.

Using equation (i) we can write, 1641280054331

Viscosity is also defined as the shear stress required to produce unit rate of shear strain.

The units of viscosity is obtained by putting the dimensions of the quantities in equation (i)

1641280054439

In MKS system, the force is represented by kgf and the length is represented by metre (m), in CGS system, the force is represented by dyne and the length is represented by cm and in SI system the force is represented by Newton (N) and the length is represented by meter (m).

MKS unit of viscosity =

CGS unit of viscosity =

is also known as Pascal and is represented by ‘Pa’.

SI unit of viscosity = = .

SI unit of viscosity = Newton –sec/m2

The unit of viscosity in CGS is also called Poise which is equal to

The numerical conversion of the unit of viscosity from MKS unit to CGS unit is given below:

One Newton = one kg (mass) x one (m/s2)(acceleration)

If viscosity is given in Poise, it must be divided by 10 to get its equivalent numerical value in SI units. Sometimes a unit of viscosity as centipoise is used where

1 centipoise = 1/100 Poise

The viscosity of water atis 0.01 Poise or 1.0 centipoise.

Related Topics,

Types of Viscosity

There are two types of viscosity

1. Kinematic viscosity

It is defined as the ratio between the dynamic viscosity and density of fluid. It is denoted by the Greek symbol () called ‘nu’. Mathematically, it can be represented by,

The unit of Kinematic viscosity is obtained as

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In MKS and SI, the unit of Kinematic Viscosity is while in CGS units it is written as. In CGS units, Kinematic Viscosity is also known as stoke.

One stoke =

Centistoke = 1/100 stoke

2. Dynamic Viscosity

It is the ratio of Force multiplied by time to the Area.

It is expressed as

The factors on which viscosity depends are:-

a. area of contact of two adjacent layers,

b. velocity difference between two adjacent layers,

c. the distance between two adjacent layers.

Difference between Dynamic Viscosity and Kinematic Viscosity

S.NO	Dynamic Viscosity	Kinetic Viscosity
1.	It is resistant to fluid flow and tells about the thickness of fluid. For example: - If the fluid is thinner, it will have less viscosity and if the thickness is more, it will have more viscosity.	It is the ratio of the fluid’s viscous force to the inertial force.
2.	Its symbol is .	Its symbol is .
3.	The unit of Dynamic Viscosity is.	The unit of Kinematic Viscosity is.
4.	Dynamic Viscosity is absolute viscosity or simply viscosity.	Kinematic Viscosity is momentum diffusivity.

Newton’s Law of Viscosity

Newton’s Law of Viscosity states that the shear stress on a fluid element layer is directly proportional to the rate of shear strain. This constant of proportionality is called the coefficient of viscosity. Mathematically, it can be expressed as

Fluids which obey the above equation are known as Newtonian fluids and the fluids which do not obey the above relation are called Non-Newtonian fluids.

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