Blast size determines how many pieces are left behind.
Exploding eggs might help investigators work out the causes of industrial explosions or airline disasters, according to researchers who have been smashing egg-shells.
The distribution of sizes of fragments left after a blast can be used to work out the pressure of the explosion, say Ferenc Kun of the University of Debrecen in Hungary and his co-workers1.
The relationship between the size of the bits and the pressure holds true for any sealed shell, they say, from an egg to a gas tank or a plane. They suggest their work could be used by forensic scientists trying to work out the size of a bomb used to blow something up, or the cause of an explosion in a chemical plant.
The team worked out the relationship by smashing up hens' eggs. They emptied the eggs by blowing out the contents through a small hole, in the same way that a child might make an Easter egg, and filled the dry, empty shells with hydrogen gas.
Igniting the mix of hydrogen and air caused the eggs to explode. The whole thing was enclosed in a plastic bag, so that when the egg blew apart, the researchers could collect all the fragments and measure their sizes.
They found that as the explosive pressure increased, there were more fragments, but fewer large pieces.
Eggs catapulted on to the ground by rubber bands also broke into a predictable distribution of pieces, but generally there were fewer bits than after an explosion.
The mathematical equations that predict the number of pieces of each size can be described by something called a power law, the team reports in a paper on the physics website arXiv.
Other researchers have found similar power-law relationships for the fragments produced by shattering a pane of glass or breaking a solid object, such as a stone. But the numbers work out slightly differently for hollow shells, says Kun's colleague Hans Herrmann of the University of Stuttgart.
Herrmann speculates that their mathematical formula could also be used to figure out the size of fragments missing from broken archaeological vessels, provided that enough shards are found to map out the overall size distribution of the pieces.
The problem, Herrmann says, will be in gathering enough fragments to do any calculations. Debris in aircraft explosions can be scattered over kilometres, he says, and the smaller the fragments, the harder they are to find.
Wittel, F., Kun, F., Herrmann, H. J. & Kröplin, B. H. Preprint, http://xxx.arviv.org/abs/cond-mat/0402461 (2004).