Dynamic viscosity is sometimes referred to as "absolute viscosity".

This represents the ratio of a fluid's shear stress to its velocity gradient. It is a fluid's internal flow resistance, i.e. a measure of the resistance to flow of a fluid under an applied force.

Kinematic viscosity incorporates fluid density as part of its measurement. Thus, dynamic viscosity is a measure of force, while kinematic viscosity is a measure of velocity. That's the difference. If you divide kinematic viscosity by the fluid density, you get absolute viscosity.

On the other hand, Newtonian fluids have an inherent viscosity that does not change as you change the force applied to the liquid. This inherent viscosity can be easily and accurately measured with a capillary-type apparatus, using gravity to move the fluid.

On the other hand, non-Newtonian fluids exhibit wide variations in viscosity based on the force applied. These tests require instruments such as rotational viscometers that can measure changes over time and over a range of applied forces.

To delineate between these two types of liquids:

Dynamic Viscosity: viscosity related to the external force applied to non-Newtonian fluids.

Kinematic Viscosity: inherent viscosity of Newtonian fluids, that does not change with a change in applied force.

Regards

What is the meaning "while kinematic viscosity is a measure of velocity." ?

The formula for kinematic viscosity is 1 centistoke (cSt) equals 1 millimeter squared per second (mm2/s). This is a rate of flow. It is the time it takes to have a known amount of fluid flow at a given distance. There is no external force pushing the fluid. Only gravity is used. This means the fluid's weight or density helps it to flow. Kinematic viscosity incorporates fluid density as part of its measurement.

It represents the particle retention capacity of the fluid and quantifies its capacity to flow out (spread). The kinematic viscosity is expressed in m2/s (homogeneous to a diffusivity). It is the unit of a velocity (m/s) while maintaining a unit distance (1 m). "Kinematic" describes the motion.

Regards

Dynamic viscosity and kinematic viscosity are the two forms of viscosity that exist. Each one represents liquid flow in a distinct way. When the density of the fluid is known, they can be used interchangeably.

The ratio of shear stress to shear rate determines a fluid's dynamic viscosity.

The ratio of viscous force to internal force determines a fluid's kinematic viscosity. The diffusion of mass and heat is analogous to kinematic viscosity.

In addition to all the interesting answers, Prof. Wan Zhihua

Please check the wonderful simulation of viscosity in the following CC commons Wikipedia article

https://en.wikipedia.org/wiki/Viscosity

The monography * stresses the importance of the difference between the two, the wiki article points out that difference:

* Landau, L. D.; Lifshitz, E.M. (1987). Fluid Mechanics (2nd ed.). Elsevier. ISBN 978-0-08-057073-0

Best Regards.

Bachir Achour ,Why there is no external force?In the Newton viscous experiment, there is the push force.

Prof. Pedro L. Contreras E. ,I cannot see the Wikipedia, could you paste it for me, moreover, could you send the e-book for me if you have it?Thank you.

Muhammad Talha ,what is the internal force, is it gravity force? I want to know whether the gravity force is g(9.81) or density?

What language are you using to check the wikis Prof. Wan Zhihua ?, try please English or Russian translation of the wiki.

I show here two screenshots of the simulation, but I prefer you to refer to the wiki post, they explain it with equations.

https://upload.wikimedia.org/wikipedia/commons/4/44/Viscosities.gif

The L&L book I mentioned can be found in the English language in Djvu format, is a monography for specialists, the vol 6 of the 10 books course on theoretical physics. Type in Google the name and you will find it. Why did I mention, the book? well, it explains, where and why the two viscosities can be used. It elaborates fluid mechanics comparing the two expressions in some chapters.

Best Regards.

Prof.

when we compare different fluids, which viscosity should we use ?Pedro L. Contreras E.

Dear Wan Zhihua Let follows as I said, L. Landau & E. Lifshitz monography (Vol 5) in Fluid Dynamics, chapter 2, then:

Dynamic viscosity (η - eta):

• It indicates the ratio of the shear stress that occurs when fluid layers move in relation to one another.
• It is a measure of a fluid's resistance to flow or deformation. It is pressure - P independent if the temperature T is fixed, we have the isothermal sound speed.
• CGI units: cm2/s
• It is the one in the Navier Stokes equation, it is comparable to pressure, it is given in the stress tensor σik = - P δik + η (∂ vi/ ∂ xk + ∂ vk/ ∂ xi)

KInematic viscosity (ν - nu)

• It is the ratio of dynamic viscosity to fluid density ν = η/ρ.
• It is inverse proportional to pressure P, i.e., ν ~ P-1
• CGI units: (gr/cm) s

An example where they are different is the common air at T = 20 C, in that case, since sound velocity depends on pressure, we have that η = 0.00018 (gr/cm) s and ν = 0.15 cm2/s.

If a fluid is ideal the viscosity won't matter since there is no internal friction, but if the fluid is not ideal, then we have the so-called kinematic viscosity kinetic coefficient kν.

Best Regards.

Pedro L. Contreras E. ,Prof,could you send the book "L. Landau & E. Lifshitz monography (Vol 5) in Fluid Dynamics, chapter 2," to me ,thank you so much. I know the definition of both viscosity, but I do not know which is suitable to use when compared with different fluids.

Dear Wan Zhihua

Write me to the private mail, follow my upgrades, I cannot post it here. Copyright Rules.

On the other hand, the rule is simple, gases, use the kinematic, for liquids use the dynamics. LL explains it well. For water for example η & ν are the same. But for reacting gases in astrophysics and plasma applications the two coefficients are different.

Best Regards.

Dear Prof. Pedro L. Contreras E. , could you send your private email to me? Are you sure "gases, use the kinematic, for liquids use the dynamics."?

All is the L&L monography, Dear Wan Zhihua.

On that book: Landau & Lifshitz, Vol 6 Second edition, Pergamon Press 1982 pp. 551. Page 46

Pedro L. Contreras E. ，thank you Prof Contreras, when I find the book, it has been already 21 hours, which I cannot read it, could you send it to my email ([email protected]), thank you so much.

In addition, the above table just say liquid and gas has different kinematic and dynamics viscosity, it cannot say that "gases, use the kinematic, for liquids use the dynamics."

Dear Wan Zhihua the kinetics of astrophysicist plasmas says it, that is why I tell you that between liquids and gases (plasmas) there are differences among the 3 (normal gases, reacting gases - plasmas and liquids) viscosities.

I wrote a couple of papers with a teacher, dedicated to the subject of astrophysical reacting gases, and it is noticeable.

For Hydrogen plasmas, the difference is that they are reacting gases, and combination and recombination of particles play a role, hence the fluctuations also are quite strong and most of the universe is Hydrogen (plasma) reacting gases. But is a difficult subject to learn.

I will send it to you on the weekend.

I hope you learn something from my posts. In liquids L (the angular momentum is not conserved), but in gases is conserved if we treat them as ideal particles (as in a first-year course in mechanics).

Best Regards.

dynamic viscosity is a measure of force, while kinematic viscosity is a measure of velocity. That’s the difference.

If you divide kinematic viscosity by the fluid density, you get absolute viscosity.

Kinematic viscosity incorporates fluid density as part of its measurement. Thus, dynamic viscosity is a measure of force, while kinematic viscosity is a measure of velocity. That's the difference.

Dynamic viscosity is a measure of force, while kinematic viscosity is a measure of velocity.