Wednesday, September 4, 2013

the tippe-top

Perhaps the most famous of physics toys: the tippe-top. Give this mushroom shaped top a spin on a semi-smooth surface and it will not only invert but change spin direction as it jumps onto its stem.

Here is a precision tippe-top made of aluminum in action:

A post shared by physicsfun (@physicsfun) on

The dynamics of this top's behavior has been analyzed in numerous scientific papers, perhaps most famously in this paper by MIT physicist Richard Cohen published in 1974.  The inversion is primarily due to a torque applied to the top from slipping friction at the top's point of contact with the table. Torque, applied to existing angular momentum, leads to this dramatic inversion of the top's spin axis. The essence of Cohen's analysis is wonderfully captured in this short description and diagram by Frans Bilsen (caution- applied vector analysis involved).

No physicist can resist the allure of this physics toy, as this photo of two Nobel Laureates "demonstrating" the tippe-top will attest!

Figure: Wolfgang Pauli and Niels Bohr demonstrate a 'tippe top' toy at the inauguration of the new Institute of Physics at Lund, Sweden (1954) 
Photograph by Erik Gustafson, courtesy AIP Emilio Segre Visual Archives, Margrethe Bohr Collection

Educational Innovations has reasonably priced wood tippe-tops in their shop:

From Educational Innovations: BUY NOW Tippe-Tops
From Amazon: BUY NOW Tippe-Tops

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