Book 31, Question 54
Why is an eggshell strong even though it is thin?
An eggshell is curved like an arch, and arches spread out pressure so that no one spot gets crushed.
When you push on the ends of an egg, the force travels around the curve of the shell. That makes it hard to break from the outside. But a chick can break out from the inside using its egg tooth, because it pushes on one weak spot.