Author: Moffatt, H.K.
Description: It is a fact of common experience that if a circular disk (for example, a penny) is spun upon a table, then ultimately it comes to rest quite abruptly, the final stage of motion being characterized by a shudder and a whirring sound of rapidly increasing frequency. As the disk rolls on its rim, the point P of rolling contact describes a circle with angular velocity |[Omega]|. In the classical (non-dissipative) theory, |[Omega]| is constant and the motion persists forever, in stark conflict with observation. Here I show that viscous dissipation in the thin layer of air between the disk and the table is sufficient to account for the observed abruptness of the settling process, during which, paradoxically, |[Omega]| increases without limit. I analyze the nature of this ‘finite-time singularity’, and show how it must be resolved.
Subject headings: Circular disk; Angular velocity; Classical theory
Publication year: 2000
Journal or book title: Nature
Volume: 404
Issue: 6780
Pages: 833-834
Find the full text : http://www.nature.com/nature/journal/v404/n6780/abs/404833a0.html
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Type: Journal Article
Serial number: 362