Kinematic vs Dynamic Viscosity: Difference and Comparison

Many terms of physics are confusing due to just the presence of slight differences, but they 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, it explains the basic activities happening around us.

Key Takeaways

1. Kinematic viscosity measures a fluid’s resistance to flow due to internal friction and is expressed in centistokes (cSt).
2. Dynamic viscosity measures a fluid’s resistance to flow due to external forces and is expressed in centipoise (cP).
3. Dynamic viscosity is more commonly used in engineering applications than kinematic viscosity.

Kinematic vs Dynamic Viscosity

Kinematic viscosity is a measure of the internal resistance of a fluid to flow under gravitational forces and is the ratio between dynamic viscosity and density. Dynamic viscosity depicts the resistance that happens when one layer of fluid moves over another layer of fluid, but it depends on the density.

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

To measure it, the capillary inside a calibrated viscometer is under a 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 a fluid, the more density and the thicker the fluid. The temperature change also affects the viscosity. With the increase in temperature, the viscosity tends to decrease suddenly.

Comparison Table

Parameters of Comparison	Kinematic Viscosity	Dynamic Viscosity
Represents	Both inertia and viscous force	The 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 a fluid’s internal resistance under the influence of the gravitational forces of a planet.

To measure it, the capillary inside a calibrated viscometer is under a 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 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 with kinematic viscosity. In terms of dependency on density, kinematic viscosity is dependent on the density of the fluid.

Kinematic, viscosity is also known as diffusivity of momentum and is 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 a fluid, the more density and the thicker the fluid. The temperature change also affects the viscosity.

With the increase in temperature, the viscosity tends to 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, dynamic viscosity must be calculated.

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

1. 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.
2. 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 for dynamic viscosity, ‘μ’ is for representation.
3. 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 kinematic viscosity.
4. In terms of dependency on 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.
5. 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.
6. 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.
7. Lastly, they differ in terms of their units; kinematic viscosity = m2/s, whereas the unit of dynamic viscosity = Ns/m2.

References

1. https://www.sciencedirect.com/science/article/pii/S0924424708004792
2. https://www.sciencedirect.com/science/article/pii/S0306261912002140
3. https://www.sciencedirect.com/science/article/pii/S0167732217356234