It's Easter as I write this, the perfect time to think deep thoughts about eggs.

Our parents told us not to play with our food. Still, have you ever taken a hard-boiled egg and spun it on a table? It turns out that, given enough spin1, an egg will (temporarily) stand up on one end.

This is puzzling to most people, but usually such everyday puzzles have a simple scientific explanation. Not this one, though! For years, physicists have been shaking their heads at this phenomenon, stating that "the eggs are acting in a way not in accord with the laws of physics." That's a highbrow way of saying they were puzzled too.

Now, in a recent article in Nature2, the mathematicians Keith Moffat (Cambridge) and Yutaka Shimomura (Keio, Yokohama) offer an explanation. According to Moffat, "the egg sacrifices spin energy to achieve its rise." Spinning energy, translated into a horizontal force, pushes the egg upright.

Apart from the required minimum speed, friction plays a crucial role. Sufficient friction gives the egg something to push against as it rights itself up. The spinning egg trick will not work on a perfectly smooth surface, nor on one that has too much friction. Also, the egg must be hard-boiled; if it isn't, too much energy is transferred into swirling around the fluid contents of the egg.

I admit to not having read my reference2's reference, the original article3 in Nature. Not being a mathematician, I'm afraid I wouldn't have understood it anyway.

Notes and References

  1. A vigorous twist of the wrist, about 10 revolutions per second.
  3. Moffatt, H.K. & Shimomura, Y.
    Spinning eggs - a paradox resolved.
    Nature, 416, 385 - 386, (2002).