Dynamic and kinematic viscosity and how they relate

[mitch_1211]

I have been looking into how the overall viscosity of a liquid/gas is related to kinematic and dynamic viscosities.

I have used n_water = 1e-3 Pa.s
n_air = 17.4e-6 Pa.s
density_water = 1000 kgm^-3
density_air = 1.3 kgm^3

and kinematic viscosity v = n/density

So v_air ~ 1.4e-5
v_water ~ 1e-6

So here the dynamic viscosity of water is greater than that of air, but the kinematic viscosity for water is less that that of air.

Does this mean that air is the more viscous fluid? How would one use there two properties to describe the overall viscosity of a fluid?

Mitch

 

[cjl]

Typically, when people refer to viscosity, they are referring to the dynamic viscosity, not the kinematic viscosity. So, I would describe water as more viscous than air.

 

[boneh3ad]

Typically, when people refer to viscosity, they are referring to the dynamic viscosity, not the kinematic viscosity. So, I would describe water as more viscous than air.

To add onto this, viscosity's chief use, relating velocity gradients in a fluid to shear stresses, involves dynamic viscosity, $\mu$. Kinematic viscosity is more of a value of convenience used because it can help simplify the notation sometimes. Dynamic viscosity is the more physically meaningful quantity in the most basic sense.

 

[mitch_1211]

I was thinking that was the case. Thank you both for the explanations.