The Ekman layer and why tea leaves go to the center of the cup

Document Type

Article

Publication Title

Physics Teacher

Publication Date

2-1-2010

Abstract

Consider a transparent, cylindrical container filled with water and sitting in the center of a record player turntable. When the turntable is started suddenly, the container rotates with the turntable, but the bulk of the fluid initially remains at rest. A thin (~1 mm) viscous boundary layer (Ekman layer) forms almost immediately at the bottom and top (if there is a lid) of the fluid. Here we describe a laboratory or demonstration exercise in which we use dye crystals1 and fine particles2 as tracers to study the flow in the Ekman layer. We also give a general method for using fine particles to measure the time it takes for the bulk of the fluid to rotate with the turntable (spin-up time) for different rates of rotation and fluid depths.

Volume

48

Issue

2

First Page

96

Last Page

100

DOI

10.1119/1.3293655

ISSN

0031921X

E-ISSN

19434928

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