When you smash two eggs together, why does only one of them break?

The Nysgjerrigper Prize of the year - 2002

This year’s winner of the ”Nysgjerrigper” prize:

When you smash two eggs together, why does only one of them break?

The road to victory began one day when Karoline was going to bake a chocolate cake. She started off with two eggs, smashed them together and found that only one of them broke “Well, I wonder why that happened?”, she wondered. So she took another couple of eggs, and then two more, and the same thing happened every time: only one of the eggs broke.

Karoline told some of her class-mates about what had happened, and soon 11 of the pupils in the Primary 7A class at Vevelstadåsen School in Akershus County were busy finding out why every time you knock two eggs together, only one of them breaks.

But why?

After studying the details of how an egg is constructed, and having thought and considered the matter a bit more, they drew up a set of the most likely hypotheses or theories to be tested to answer the question: why does only of of the eggs break?

• If one of the eggs is moving faster than the other, then that is the one that will break.
• They cannot both break because the egg that gets broken is no longer strong enough to break the other one: the broken egg has become weaker.
• Perhaps it has something to do with the weight and size of the egg?
• One of the eggs may have a thicker shell than the other.
• All eggs are different, since the come from different hens.
• It depends on which part of the eggshells are knocked against each other (e.g. narrow end against narrow end).

Forty eggs

In order to test their hypotheses, the pupils drew up a plan. They wanted to know as much as possible about eggs, carry out a series of experiments and talk to someone who knew a lot about hens and eggs. Karoline and her associates got down to work: they bought 20 eggs from one shop and 20 from another, so as to be quite sure that they came from different farms. Then they numbered the eggs at random and weighed them on a very accurate laboratory balance. To measure the length and width of the eggs they used something called a calliper gauge. And to measure the thickness of the shell they got hold of a micrometer (an instrument for measuring very small distances). All their data were put into a table.

Egg-breakers

Forty eggs to be sacrificed! To test the first hypothesis (If one of the eggs is moving faster than the other, that is the one that will break) the young scientists chose eggs at random and smashed them together in various ways; narrow end against narrow end, blunt end against blunt end, side against side, narrow end against blunt end, blunt end against side and narrow end against side. So as not to miss anything, they videotaped the experiment. Every single time, the egg that was not in motion was the one that broke. So much for that theory!

Can a broken egg destroy another egg? This time they used a vice from the carpentry workshop to squeeze the eggs together. From their report: “When on of the eggs breaks, the other eggs continues to force its way into the broken egg. The egg that is still whole continues to break up the other egg by making its way right through it, just like a snowplough that pushes ahead and shoves everything ahead of it to the side”.

Can the size or weight of the eggs have any influence on which egg gets broken? No, say the pupils, basing their answer on yet another experiment. However, the thickness of the eggshell may tell us something about which egg breaks first, since the tests showed that the egg with the thinnest shell is usually the first to give up.

A farmer whom the research team talks to tells them that even a tiny irregularity can cause an egg to break. He thought that the blunt end is usually the strongest part of an egg. Another farmer agreed that most get broken at the narrow end.

Conclusions

In their conclusions, the class wrote: “Every time you smash to eggs together only one egg will break because there is always a tiny little difference between the thickness of the two shells. The broken egg will not damage the whole egg because it has no strength left. This shows that hypotheses 2, 4 and 5 are the most correct”.

A new problem!

The pupils discovered that at the blunt end of each egg there is an air-pocket, a sort of “airbag”, which leads them to suggest that it is the blunt end of the egg that comes out of the hen first. They take their new problem to other experts on hens: does the “airbag” act as a sort of protective cushion for the egg as it hits the ground? They are given a lot of different answers, but the Agricultural University in Ås confirms that yes, it is the blunt end that emerges first. Whether the airbag acts as a cushion is not something the scientists had thought of. So perhaps Vevelstadåsen School’s Nysgjerrigper gang have given the poultry scientists something to think about!