Feynman’s wobbling plate

Abstract

In the book Surely You Are Joking, Mr. Feynman! Richard Feynman tells a story of a Cornell cafeteria plate being tossed into the air. As the plate spun, it wobbled. Feynman noticed a relation between the two motions. He solved the motion of the plate by using the Lagrangian approach. This solution didn’t satisfy him. He wanted to understand the motion of the plate by analyzing the motion of its individual particles and the forces acting on them. He was successful, but he didn’t tell us how he did it. We provide an elementary explanation for the two-to-one ratio of wobble to spin frequencies, based on an analysis of the motion of the particles and the forces acting on them. We also demonstrate the power of numerical simulation and computer animation to provide insight into a physical phenomenon and guidance on how to do the analysis.

On the minimal model for the low frequency wobbling instability of friction discs

“…Even the simplest case of a free disc still attracts attention of physicists and teachers [1,2] and demonstrates an inspiring variety of effects in its dynamic behavior. Although friction discs are quite usual in technical applications, their dynamics didn't attract much attention in the past.…”

Analogies of the classical Euler top with a rotor to spin squeezing and quantum phase transitions in a generalized Lipkin-Meshkov-Glick model

“…Feynman was surely joking when telling this story to R. Leighton who collected Feynman's memories, because the situation is just opposite: the wobbling is twice as fast as the rotation. This follows from the above arguments, and was clearly explained in a note by B. F. Chao [76] four years after Feynman's book, as well as in a more detailed study in [77].…”

O legado de Feynman visto por pesquisadores brasileiros

“…Voltou-se para sua intuitiva formulação Lagrangeana da mecânica quântica proposta na sua tese de doutorado [20] e iniciou conversas com Dirac. Teve dificuldades em mostrar suas ideias em artigo, que continha parte de sua tese de doutorado (a qual não conseguiu publicar por causa do esforço de guerra em Los Alamos), mas foi encorajado por colegas.…”