How to tell a boiled egg from a raw one

Do you know how, without breaking the shell, to determine whether an egg is cooked or raw? Knowledge of physics will help you to successfully get out of this little difficulty.

The fact is that boiled and raw eggs do not rotate in the same way. This can be used to solve our problem. The test egg is placed on a flat plate and rotated with two fingers.

A boiled (especially hard-boiled) egg rotates much faster and longer than a raw one. The latter is difficult even to make to rotate; meanwhile, a hard-boiled egg spins so quickly that its outlines merge for the eyes into a flattened white ellipsoid and it can stand on its own sharp end.

The reason for these phenomena lies in the fact that the hard-boiled egg rotates as a solid whole; in a raw egg, its liquid content, not immediately receiving a rotational movement, delays, due to its inertia, the movement of the solid shell; it acts as a brake.

Boiled and uncooked eggs also relate differently to stopping rotation. If you touch a spinning boiled egg with your finger, it stops immediately. A raw egg, stopping for a moment, will rotate a little more after removing the hand. This happens again as a result of inertia: the internal liquid mass in a raw egg still continues to move after the solid shell has come to rest; the contents of the boiled egg stop at the same time as the outer shell stops.