What it shows:
Eggs have a reputation for being quite strong under compressional loads. You won't believe your eyes when you see how strong they actually are — an egg can support a person!
How it works:
An egg shell is a composite material, but primarily calcium carbonate, "nature's ceramic."1 We assume the ultimate compressional strength of the material to be about the same as bone (which is mostly calcium phosphate, but never mind): 170x106 N/m2. The diameter of a "large" chicken egg is about 1.75" and the typical shell thickness seems to be around 0.023". Thus, the cross-sectional area of the shell wall is approximately 1/8 sq in, or 8x10-5 m2 which, when combined with the ultimate strength, theoretically will support a 1.4x104 N load (3,000 lbs)! That's theoretical, but in practice it's not anywhere near that. On the other hand, what it will support is nothing to be sneezed at.
Setting it up:
The apparatus that holds the egg and aligns the load on top of it is an old discarded Carl Zeiss optical stand that we have modified for this purpose. (We also use the stand for the compressional strength of chalk — yes, that's calcium carbonate too). The egg is cushioned by a hemispherical cap made of Sorbothane, one above and one below (see photo). Lead bricks are added, one at a time, on top of the egg. Each lead brick weighs 25 lbs and one egg supported 10 bricks! Yes, you could just stand on the egg without breaking it.
Comments:
When one of us (Wolfgang) first saw Dick Berg demonstrate this at the University of Maryland, he knew we just had to add it to our repertoire!
1 Steven Vogel, Comparative Biomechanics, (Princeton University Press, 2003), p. 313