Question

Is Stokes' law valid for droplets of oil falling in water? For air bubbles rising in benzene? For tiny particles falling in air, if the particle diameters are of the order of the mean free path of the molecules in the air?

Answer 1

1. Stokes law is valid for any object falling in water or any other liquid, Yes stokes law can be used for liquid oil falling in water provided that the Oil droplet Reynold no shall not be more than 20.

2. Stokes law defines the foam and skin drag on the droplet, yes it is applicable for the gas bubbles but make sure of Reynolds number.

3. Reynold number can be used for the tiny particle in air.

4. For a particle of the order of mean free path of the molecule is generally governed by the Brownian motion hence stokes law is not applicable in that case.