The egg drop challenge is an annual rite of passage for many students learning about physics: Swaddle an egg in cotton balls and masking tape or other materials, and then drop it off the roof of your school. Anyone who has participated in this exercise knows how difficult it is to engineer a structure that will save the egg from a messy end. (It certainly was not my bespoke foam core creation in middle school.)
Once the eggs are broken, teachers may reveal insights into the physics of impact, including the claim that eggs sitting vertically crack less often than eggs sitting horizontally.
But is that really true?
After running egg drop challenges for university freshman, Tal Cohen, an engineering professor at the Massachusetts Institute of Technology, began to wonder whether that assertion really fit the picture of a falling egg.
“It’s based on the static behavior of an egg,” she said. “Dynamic impact is quite different.”
To assess whether she was telling students the right story, she headed to the lab, eggs in tow, and performed some tests. What she found suggested the truth was more complicated, and in a paper out Thursday in the journal Communications Physics, she and her colleagues report that eggs lying horizontally are actually less likely to crack.
To perform their experiments, the researchers first headed to Costco and picked up more than 200 eggs (this at a moment in 2023 when eggs were cheaper than today). Then the team crushed some in a device that allowed them to record the force required to crack the shells. They found that eggshells cracked under about the same force regardless of whether they were lying down or sitting up in the device.
They then actually dropped the eggs. For experimental purposes, they dropped them from tiny heights — just eight millimeters or so. That was so they could see a variety of outcomes. If they dropped the eggs from bigger heights, all of them broke regardless of orientation.
An important difference between the positions was observed. Eggs dropped so they landed on their sides were substantially less likely to crack. When they hit, the shell was able to compress, absorbing some of the blow. Eggs dropped on their ends, where the shell is stiffer, did not show such flexibility.
There’s an analogy to be drawn to the human body, said Joseph E. Bonavia, an M.I.T. graduate student in engineering and an author of the paper.
“If you are falling from a height, you don’t want to lock your knees. You’ll break your bones,” he said. “You want to bend your knees — that’s what the egg is doing.”
The way we cook eggs may have contributed to the widespread misunderstanding that the side of the egg is most fragile, said Brendan M. Unikewicz, also an M.I.T. graduate student and another author of the paper. That’s because we usually crack eggs in half at the midpoint. Breaking the horizontal side results in long cracks that can split the shell in half cleanly, while cracking eggs on their tips, as these experiments showed, results in the shell collapsing inward — not, in other words, the optimal outcome for making an omelet.
Indeed, the experiments reveal that our intuition about what happens in real-life scenarios where an object is falling cannot always be relied upon, Dr. Cohen said. This is why it is important for engineers and students of engineering to remain open to challenging conventional wisdom, she said.
Did anyone eat the eggs? By university policy, humans are not allowed to consume experimental materials after they’ve entered the lab. But Dr. Cohen’s dog, under no such prohibition, had some hearty meals.
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