Skip to comments.Mathematicians Solve Egg-Spin Mystery
Posted on 03/29/2002 4:58:19 PM PST by randog
Just in time for Easter, mathematicians have cracked the mystery of why a hard-boiled egg spun on a tabletop rises on one end and whirls like a top.
The explanation, in an eggshell: Friction.
Mathematicians from England and Japan spent six months filching eggs from their families' refrigerators and trying to explain the mysterious forces controlling this behavior. Their findings appear in Thursday's issue of the journal Nature.
Keith Moffatt of the University of Cambridge in England and Yutaka Shimomura of Keio University in Japan believed that demonstrating how this effect works would be a simple, fun exercise. Instead, it "turned out to be very subtle and quite tricky," Moffatt said.
Their report contains no fewer than 16 equations in less than two pages.
Here is an explanation for the spinning Easter egg conundrum, without the mathematics:
Imagine an egg spinning on its side on a tabletop. Because of the curve of its shell, it is touching the table at only one point. But the contact point is not fixed; it slides in a small circle around an imaginary vertical axis.
As the egg slides across the table, the friction created slows the egg's rotation slightly, and the contact point with the table moves off-center. The egg begins to twist as it spins. One end slowly rises until the egg stands vertically. For a few seconds, anyway.
The egg can be any size or type. But it must be hard-boiled.
"When you try to spin a soft egg on a table the liquid fluid inside lags behind the shell," Moffatt said. "You set the shell in motion but the fluid doesn't want to spin up. By the time the fluid is spinning at the same time as the shell, it's lost a lot of kinetic energy and it's just not got enough remaining to stand up on its end."
Or in non-scientific terms: Splat.
And these people are considered intelligent? Think of how much government grant money that could have had for a multi-year project to produce the same results...
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