The dynamics of spin

Dynamics of spin Spin a hard-boiled egg on a table and it will rise to the vertical. Why?

Professor Keith Moffatt FRS, Ms Kiran Singh, Mr Juri Sobral and Dr Tadashi Tokieda, University of Cambridge
Dr Michal Branicki, University of Bristol
Dr Andrew Burbanks, University of Portsmouth
Professor Yutaka Shimomura, Keio University, Yokohama, Japan

Spinning toys: surprising dynamics and tantalizing connections to natural phenomena

Researchers from the Universities of Cambridge, Bristol and Portsmouth and from Keio University (Japan) are using mechanical toys to illustrate behaviours that seem to defy the laws of physics.

“Spinning toys are not only fun to play with, they can also illustrate fundamental principles of dynamics,” says Professor Keith Moffatt from the University of Cambridge. “Understanding their behaviour can help us understand other more complex natural phenomena such as the evolution of weather patterns or the magnetodynamics of spinning stars and planets.”

 The toys to be exhibited include spinning eggs that rise against gravity (a result of dissipative instability); skew objects (known as rattlebacks) that spontaneously reverse their sense of spin (a result of chiral instability); and spinning discs that roll at an accelerating rate towards a crisis point (known as a finite-time singularity) at which motion suddenly ceases. Mathematics, coupled with computation and high-speed photography, provides explanations for each of these surprising and counter-intuitive behaviours. These explanations reveal dynamical mechanisms that have potential applications on scales ranging from the microscopic to the astrophysical.

This exhibit commemorates the great Swiss mathematician Leonhard Euler (1707-1783) whose 300th anniversary is celebrated this year, and who first obtained the governing equations of rigid-body dynamics.