Dear students if you are looking for **definition**, unit and explanations of **Dynamic** and “**Kinematic viscosity“** then you are the right place. here we are details discussion about these.

**Definition of Dynamic Viscosity:**

It is also known as or **absolute or simple viscosity**. It is defined as the property of a liquid which offers resistance to the movement of one layer of a liquid over another adjacent layer of liquid. The viscosity of a liquid is due to cohesion and interaction between particles.

Another way , it is the property of a fluid which influences the fluid motion to a great extant. It is the property by virtue of which a fluid offer resistance to deformation under the influence of a shear force.

The shear force remains in existence the fluid undergoes a continuous deformation. For a given fluid, the rate of deformation is dependent upon the magnitude of the shear force.

The molecular friction or shear resistance the fluid opposes such continuous deformation.

If A is the area of the moving surface and F is the force required to move the surface at a constant velocity, it has been established that the shear stress F/A is directly proportional to the time rate of deformation, thus

F/A=µdθ/dt

Where, µ is the proportionality constant and is called coefficient of viscosity or the dynamic viscosity**.**

Water, air, blood, oil all are viscous fluid.

**The dynamic viscosity of water** is 8.90×10^{-4 }Pa.s

__Unit of dynamic viscosity__:

SI unit = N-s/m²

Pascal second is also the SI unit of viscosity. 1Pa.s=1 N-s/m²

C.G.S Unit = dyne-s/cm² C.G.S unit is also called **poise.**

**1 poise=1** dyne-s/cm²

1 poise= 0.1N-s/m² or 1Pa.s=10 poise

**Dimension : **Its dimension is M°L^{-1}T^{-1}

**What is Kinematic Viscosity?**

It is defined as the ratio of dynamic viscosity to the density of liquid.

Mathematically,

**Kinematic viscosity **= dynamic viscosity/density of liquid

=µ/ρ

**Unit of “Kinematic Viscosity”: **

In SI unit the unit of kinematic viscosity is m²/s and C.G.S unit cm²/s

C.G.S unit is also called stoke. 1 stoke= 1 cm²/s =10^{-4 }m²/s

**Dimension=M**°**L**²T^{-2}

## Difference Between Dynamic & Kinematic viscosity

Dynamic Viscosity | Kinematic Viscosity |

It is the resistance force of liquid particles | It is the ration of dynamic viscosity to the density of liquid |

It,s SI unit is N/m | It,s SI unit is m²/s |

Dimension is M°L²T^{-2} |
Dimension is M°L^{-1}T^{-1} |

**Compressibility:** It is that property of a liquid by virtue of which liquids undergo a change in volume with change in pressure. The compressibility is the reciprocal of bulk modulus of elasticity, which is defined as the ratio of compressive stress to volumetric strain.

Surface tension: It is the property of a liquid which enables it to resist tensile stress. It is denoted by sigma(σ). The unit of surface tension is N/m

**Cohesion Force**: The molecular attraction among the particle of same liquid by which it can contract in a small place is called cohesion force. The surface tension is due to cohesion force of liquid.

**Adhesion force: **The force by which a liquid particles attracted differents liquid or solid particle is called adhesion.

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