copyright © 2003, Alice Held, All Rights Reserved

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 egg-shell: Friction.

Mathematicians from England and Japan spent 6 months filching eggs from their families' refrigerators and trying to explain the mysterious forces controlling this behavior. They believed that demonstrating how this effect works would be a simple, fun exercise. Instead, it "turned out to be very subtle and quite tricky."

Their report contains no fewer than 16 equations in less than 2 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. 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!