The Science of Fresh and hardboiled eggs
How do you tell if an egg is fresh or hardboiled? Well, you could just crack it open, but that might waste a lot of eggs. A better way is to spin it.
A hardboiled egg will spin quite easily, but if you just touch it with your finger to stop it spinning, it will stay stopped.
However, a fresh egg, which is harder to get spinning, will start spinning again just after being stopped.
This is because the inside of the fresh egg is liquid. Therefore, when you stop the shell of the egg, the liquid inside still keeps spinning a bit, and drags the shell around with it when you let go.
For the hardboiled egg, the inside is solid and so the whole egg (shell, white and yolk) stops spinning together.