A question for Easter

[jake-the-peg]

If I take a hard boiled egg that is laying down on it's side and spin it, it will go around a few times and then come up onto it's pointed end and spin there for a while like a top.

Why is this?

[MargeB]

Depends on the temperature of the room. And atmospheric pressure

[Clanad]

Normally, a rapidly spinning object will preserve its direction of spin--the reason a fast-moving bicycle doesn't topple over. But in the case of a hard-boiled egg, friction between the egg and the tabletop changes the direction of this angular momentum,

Although the egg starts out spinning horizontally, this position isn't stable, so any tiny irregularity in the eggshell or table will tilt the egg slightly. This kicks off an escalating cycle: The change to a tilted spin makes the egg slip on the tabletop, creating a frictional force that pushes the end upward. That in turn makes the egg slip more, jacking up the frictional push. Eventually, this friction shoves the egg all the way to the vertical position.

However, Easter-weekend experimenters won't get the same rise out of a raw egg. The reason is that when the egg spins, the yolk and white lag behind, gradually absorbing energy and slowing down the spin. The remaining speed is not enough to create the strong frictional forces that push the egg upright, so the egg simply slows down and stops... (With thanks to Science Now)

[jake-the-peg]

Very good,

You're missing one small extra point, the egg's center of gravity is different from it's center of rotation so that the drag from friction causes a twisting effect that swings it up onto it's nose.

Apparrently a couple of mathematecians spent 6 months a couple of years back working out the exact details :c)

Happy Easter all