Re: What is the cause of differential rotation of fluid?

Hi Erika,

There’s a nice description of the causes of differential rotation in stars in the Stellar Rotation entry in Wikipedia. Basically, angular velocity varies with latitude because convective motions redistribute mass which carries a portion of the star’s angular momentum, thus redistributing the angular velocity.

Your second example was water spiralling down a drainage hole. I’ve never heard the term differential rotation applied to this problem. There’s a common misconception that water spirals down a drainage hole in different directions in the northern a southern hemisphere. While the Coriolis Effect does govern the direction of rotation of large scale vortices, such as hurricanes, it is negligible on small scales. The direction of rotation of your sink vortex is much more strongly influenced by the shape of the basin or any tiny amount angular momentum that the fluid may have before draining commences (which will be amplified through vortex stretching).

I hope this helps.
Cheers,
Tetjana