A well-spun egg also jumps

Physicists have demonstrated that spinning a hard-boiled egg horizontally makes it jump into the air.

Scientists already knew that a fast-spinning egg spontaneously stands on its end. Random jitters during that process could amplify into leaps, researchers had theorized.

In some high-speed video images, hand-twirled eggs seemed to jump. But, no one knew whether those jumps were real or resulted from inadvertent upward propulsion from a spinner’s hand, notes Yutaka Shimomura of Keio University in Yokohama, Japan.

In new tests, he and his colleagues spun egg-shaped pieces of aluminum at initial rates of up to 2,500 revolutions per minute in a machine custom-built to impart strictly horizontal spins. By means of optical, acoustic, and electronic measurements, the team detected that the mock eggs leaped a fraction of a millimeter off the surface for up to a few hundredths of a second. During spins of actual hard-boiled eggs at 1,800 rpm, the researchers saw gaps momentarily appear beneath the eggs.

The team’s findings, reported in an upcoming Proceedings of the Royal Society: A, illuminate how tiny fluctuations in physical systems can lead to unexpected effects, Shimomura says.

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