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Name: Jonas
Status: Student
Grade: 9-12
Location: AS
Country: United States
Date: August 2006


Question:
Hi! A friend has told me it is impossible to break a raw egg by squeezing it in a palm. I have even tried squeezing it abruptly and it is really impossible. What is the physics behind this phenomenon? I am trying to squeeze the ends together.



Replies:
Hi Jonas,

Perhaps it is not truly impossible to break an egg in the way you describe, but it is extremely hard! The reason lies in understanding the attributes of the eggshell, and also the shape of the shell itself. Like many common non-ductile materials such as ceramics, bricks, glass and concrete, an eggshell is very weak in tension, but very strong indeed in compression. When you squeeze the egg as you described, the curved shape of the shell results in the forces resolving into almost pure compression within the shell. These two attributes result in the egg displaying great strength.

There are very practical applications of your experiment. One of the earliest and most important is the "arch". Bricks arranged in an arch shape (such as you probably have seen in photos of Roman aqueducts) can support tremendous loads without breaking. Just as in your egg experiment, in an arch, a force applied vertically downward resolves into pure compression in the bricks that make up the arch. Like the shell of an egg, bricks are weak in tension, but extremely strong in compression.

Excellent question! Bet you did not think that a simple experiment with an egg would result in such a significant engineering principle!

Regards,

Bob Wilson.



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