Many terms of physics are confusing due to just the presence of slight differences but contain very important information.

Physics-related every term is very important because it explains the logical activities that happen on the planet earth just like the concept of gravity hic explains the basic activities happening around us.

**Kinematic vs Dynamic Viscosity**

The difference between kinematic and dynamic viscosity is that, when both inertia and viscous force are dominant, the ratio required for it is dynamic viscosity to density (it is influence and dependent on dynamic viscosity as well), it represents both inertia and viscous forces, unit m2/s is used for it, and it is known as diffusivity of momentum whereas the dynamic viscosity is used when only viscous force is dominant, shear stress to shear strain ration is required, not influence by kinematic viscosity and is independent, represents the viscous force of the fluid, and lastly unit used for it is Ns/m2.

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Kinematic viscosity is a type of measurement of the internal resistance of fluid under the influence of the gravitational forces of a planet.

For achieving the purpose of measuring it, the capillary inside a calibrated viscometer is under the controlled temperature. A fixed amount of fluid is required to flow through a known distance in a fixed amount of time.

Dynamic viscosity indicates the resistance when one layer of fluids happens to move over another layer of fluid. It directly depends upon the density of a fluid.

The higher the viscosity of fluid happens to the more density and the thicker the fluid is. The temperature change also affects the viscosity. On the increase of the temperature, the viscosity tends to be decrease suddenly.

**Comparison Table **

Parameters of Comparison | Kinematic Viscosity | Dynamic Viscosity |
---|---|---|

Represents | Both inertia and viscous force | Viscous force of the fluid |

Symbol | v | μ |

Ratio of | dynamic viscosity to density | shear stress to shear strain |

Density | Dependent | Independent |

Also Called | Diffusivity of momentum | Absolute viscosity |

**What is Kinematic Viscosity?**

Kinematic viscosity is a type of measurement of the internal resistance of fluid under the influence of the gravitational forces of a planet.

For achieving the purpose of measuring it, the capillary inside a calibrated viscometer is under the controlled temperature.

A fixed amount of fluid is required to flow through a known distance in a fixed amount of time to measure the kinematic viscosity at the specific conditions. The value obtained through this test is only valid at those conditions like temperature.

The Kinematic viscosity is used for the representation of both inertia and viscous force. For Kinematic viscosity, the symbol used in representation is ‘v..’

The ratio used in the case of Kinematic viscosity is equal to the dynamic viscosity/density, which provides us kinematic viscosity. In terms of dependency of density, kinematic viscosity is dependent on the density of the fluid.

For kinematic, viscosity is also known as diffusivity of momentum and is generally used to refer to kinematic viscosity.

Kinematic viscosity is used when both inertia and viscosity forces are dominant. The standard unit which represents kinematic viscosity is m2/s.

**What is Dynamic Viscosity?**

Dynamic viscosity indicates the resistance when one layer of fluids happens to move over another layer of fluid. It directly depends upon the density of a fluid.

The higher the viscosity of fluid happens to the more density and the thicker the fluid is. The temperature change also affects the viscosity.

On the increase of the temperature, the viscosity tends to be decrease suddenly. The other temperature that influences dynamic viscosity also tends to increase in the state as gas as the temperature rises.

The viscous force of the fluid is represented with the help of dynamic viscosity. For dynamic viscosity, the symbol used is ‘μ’ for representation.

Dynamic viscosity the ratio used is the ratio of shear stress to shear strain. This also implies that for calculating the kinematic viscosity, the calculation of dynamic viscosity is a must.

It is not dependent on the case of dynamic viscosity. Absolute viscosity is another term used for dynamic viscosity. When only viscosity force is dominant dynamic viscosity is used. The unit of dynamic viscosity is Ns/m2.

**Main Differences Between Kinematic and Dynamic Viscosity**

- Both of them represent different things. Kinematic viscosity is used for the representation of both inertia and viscous force, whereas the representation of the viscous force of the fluid with the help of dynamic viscosity is taken.
- As mentioned above, both of them represent different things, and hence, they are also represented by different symbols. For Kinematic viscosity, the symbol is used in ‘v’ while fore dynamic viscosity ‘μ’ for representation.
- The ratio used in the case of Kinematic viscosity is the ratio of dynamic viscosity to density, while for dynamic viscosity, the ratio used is the ratio of shear stress to shear strain. This also implies that dynamic viscosity is a must for the calculation of the kinematic viscosity.
- In terms of dependency of density, both of them differ, as in the case of kinematic viscosity, it is dependent, whereas it is not dependent in the case of dynamic viscosity.
- Both of them are also called or known by other terms. Diffusivity of the momentum is another term for kinematic viscosity. Absolute viscosity is another term for dynamic viscosity.
- Both of these are used in different situations for kinematic viscosity. It is used when both inertia and viscosity force is dominant, whereas when only viscosity force is dominant dynamic viscosity is used.
- Lastly, they differ in terms of their units; kinematic viscosity = m2/s, whereas the unit of dynamic viscosity = Ns/m2.

**References**

- https://www.sciencedirect.com/science/article/pii/S0924424708004792
- https://www.sciencedirect.com/science/article/pii/S0306261912002140
- https://www.sciencedirect.com/science/article/pii/S0167732217356234

Piyush Yadav has spent the past 25 years working as a physicist in the local community. He is a physicist passionate about making science more accessible to our readers. He holds a BSc in Natural Sciences and Post Graduate Diploma in Environmental Science. You can read more about him on his bio page.