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Make an Egg Stand on End.

Could you make an egg lift up on it's end and stay there? Find out how in this experiment.

What you need

	A hard boiled egg
	A surface, like a worksurface or piece of wood.

What to Do

Hard boil an egg

Lay in on it's side on the surface

Spin the egg as fast as you can.

Does anything strange happen?

What may Happen

If you spin the egg fast enough you will find that it stands up on end.

What is going on?

Because of the shape of the egg, the point of contact with the ground is not directly above the centre of mass of the egg (this is the average position of all the mass of the object, and is the point that the object would spin around naturally.

At the Start


Because the egg is spinning around its centre of mass which is not above the point of contact, the contact point gets dragged around the surface. The friction from this (blue) applies a force on the egg.	View from the wide end of the egg. The friction applies a twisting force to the egg

Why does this force cause the egg to stand on end?

The egg is spinning so it acts as a gyroscope. Gyroscopes have a very interesting property.

A gyroscope

If you apply a twist to a gyroscope as gravity does in the case to the left (blue arrow) the gyroscope actually moves at right angles to this along the green arrow. If the gyroscope is standing up as in this picture this means that it will keep going around in a circle rather than falling over.

This means that the friction on the egg (blue arrow) wil actually cause the egg to rotate at right angles to this (green arrow) and start to stand upright.

From the side

Eventually if the egg was spinning fast enough it will stand upright.

Egg on its end

The exact dynamics of this are quite complex and were only worked out in 2002 by Keith Moffat from Cambridge.

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Listen to this as part of the show: 7th May 2006 - Dinosaurs and Fossils - Jurassic Science set in Stone
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