Spinning Eggs Caught Hopping

Using high-speed imaging and acoustic and electrical observations, scientists at Keio University in Yokohama, Japan, have confirmed that hard-boiled eggs set spinning rapidly on a flat surface on their side will stand up and jump slightly into the air. The results of their experimental investigations into this phenomenon are scheduled to be published in an issue of Proceedings of the Royal Society A and appeared in the April 12 electronic edition of the journal.

In the work, the investigators first studied the behavior of a 133-g aluminum egg-shaped spheroid, which they set spinning at various rates on a sheet of polished copper using a mechanical rotor. A video camera collected a series of 256 × 256-pixel images of the spheroid at 240 fps, revealing occasional points at which the object had jumped free of the surface. Using a microphone to monitor changes in the noise made by the object as it spun, they quantified the maximum height of the first leap at approximately 0.1 mm.

Changes observed in the capacitance of the one-plate condenser formed by the copper plate and the aluminum spheroid substantiated the conclusion that the object was hopping.

Armed with the data from the experiments with the artificial egg and with the results of numerical simulations, the scientists set their sights on real eggs. Although the acoustic and electrical signals were more difficult to detect, the video of a 67.3-g hard-boiled egg with an initial spin rate of 1800 rpm from the rotor catches the egg in midjump.

Yutaka Shimomura, leader of the research effort, characterized the work as of interest to physics in general. Although a so-called toy problem, it offers insights into the emergence of unexpected phenomena from initially small events, with potential applications in modeling of atmospheric dynamics and other turbulent flows. The team’s next step, Shimomura said, will be to investigate a more complex spinning spheroid, simulating a raw egg.