Why Does a Hard Boiled Egg Spin and Raw Egg Won't?

[Tricks67]

why would a hard boiled egg spin and raw egg won't if made to spin on a flat surface?

 

[Meir Achuz]

When you spin the shell of a raw egg, the torque is not transmitted to the liquid inside.
You can see this by rotating a glass of water with tea leaves. The leaves take a long time to spin if you spin the flass.

 

[Tricks67]

the torque is not transferred to the liquid..ok, then the reason it does not rotate is due to the imbalance of torque outside and inside?

 

[Bill_K]

For a raw egg the torque is transmitted slowly to the liquid inside. And since you usually spin an egg just once around, there is not much angular momentum that can be imparted to the egg so quickly. If you do keep on rotating it, after a few turns the yolk will pick up speed and the egg will go ahead and spin like a cooked egg.

Conversely, a standard method of determining whether an egg is cooked or not is to get it spinning and then suddenly bring it to a halt. Then release it. For an uncooked egg the yolk will not immediately stop, it will keep on going inside even after the shell is stopped. Then when you release the egg the spinning motion will resume.

 

[Tricks67]

thanks a lot!