Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: Eggs: Hard-Boiled or Raw?

Learn more physics!

Most recent answer: 10/22/2007
How do you determine which egg is cooked if given a cooked egg and an uncooked egg?
- krystal (age 17)
Hi Krystal -

If you don't mind getting egg all over, you could just break them open -- you'll find out right away which one's cooked and which one's not.

The easiest nondestructive way we know about for finding if an egg is cooked or not is to try to spin it on a flat surface. If you try to spin a raw egg, when you grab it and give it a twisting motion, only the shell and some of the liquid near the shell starts rotating -- the liquid close to the center will spin much more slowly because it isnít attached to the outside. After you let go, the friction betwen the different parts of the liquid brings them all to the same spinning rate, a sort of average, in between the slow insides and the faster outsides. The net effect is a slowly-spinning egg.

If the egg is cooked, the inside will be solid. When you spin the egg, the inside will spin together with the outside, and there will be no "catching up" to do to slow it down. The hard-boiled egg in general will stay spinning longer because it got more angular momentum from your hand and it has the same slowing torque from friction from the table.

Bob (and Tom)

(published on 10/22/2007)

Follow-up on this answer.