How to differentiate between a raw egg and one which is hardboiled,
without breaking or damaging the shells in any way

Also, some comments on the rotational dynamics of planetary bodies and satellites.

Put the egg on a table and attempt to spin it round violently by hand. The hardboiled egg will easily spin, just like any other object of similar shape. The raw egg, however, will for some reason seem to resist being spun, and will probably stop abruptly as you let go.

The reason has to do with the liquid interior of the raw egg. When you spin the hardboiled egg by hand, the entire egg is forced round; then when you let go it tends to continue under its own momentum. With the raw egg, when you spin the shell round by hand, the liquid interior (together with the semisolid yolk inside) will resist being spun; then when you let go, the friction between the (almost) stationary interior and the thin shell, will force the shell to stop spinning almost immediately.

If you were able to spin the shell of a raw egg continuously for some time, so that the liquid inside had time to build up speed (by friction with the shell), then, the egg would continue spinning when you let go.

If, in this case, you were to stop the egg spinning with your hand, and then quickly remove your hand, the shell would resume spinning, because the interior would not have stopped.

Thus, it is possible, by observing the dynamics of the outside, to tell whether the interior is solid or liquid.

In some cases, the fluidity of the interior of a planet or satellite can affect the rotational dynamics of the body.

Last updated 23 July 2006
Kieron Taylor