The egg-drop experiment is a staple topic in science classes. Students find ways to protect an egg from breaking when dropped from a certain height. Traditionally, textbooks have explained that dropping an egg upright, with one end hitting first, results in less breakage. The reality is different.
A research team led by Tal Cohen, a professor in the Department of Civil and Environmental Engineering at the Massachusetts Institute of Technology (MIT), announced on the 9th that the probability of breakage is significantly lower when dropping the egg on its side compared to standing it upright. The research findings were published in the international journal 'Communications Physics' the same day.
The researchers conducted experiments by dropping a total of 180 eggs, with 60 each from heights of 8 mm, 9 mm, and 10 mm. The results showed that eggs dropped vertically broke more often than those dropped on their side. For example, when an egg was dropped upright from a height of 8 mm, more than half broke. There was little difference in the degree of breakage regardless of which side was facing downward. In contrast, eggs dropped on their side broke less than 10% at the same height.
The team also measured the force required to crush the eggs. Regardless of whether the egg was upright or on its side, the force needed for breakage was about 45 N (newtons, a unit of force), which was similar. However, when the egg was upright, it was compressed to an average of 0.161 mm before breaking, whereas when it was on its side, it was compressed to 0.213 mm. The fact that side-laid eggs broke less suggests that they absorbed more impact as they compressed.
The researchers believe that the reason people have long thought that dropping an egg upright results in less breakage is due to a confusion between stiffness and toughness. Stiffness refers to how well an object retains its shape and resists being compressed, while toughness indicates how well it can absorb and withstand impacts.
While it is commonly thought that stiffness prevents breakage, in reality, a robust structure that disperses impact through compression breaks less. This means that eggs dropped horizontally are sturdier than those dropped vertically.
This same principle can explain why a person bends their knees when falling. Keeping the knees straight may appear sturdy, but it fails to absorb impact, making injury more likely. Conversely, bending the knees may look weak but helps distribute the impact and protect the body.
Results from a three-dimensional computer simulation conducted corroborated those from the drop experiments. By setting the yolk and white of the egg as viscous liquids and the eggshell as a brittle material, the experiment showed that when the egg falls horizontally, the force is evenly distributed across the shell, dispersing the impact.
The researchers noted, "This study extends beyond the simple egg experiment and can be applied to the design of structures that need to withstand impacts, such as buildings, vehicles, and helmets."
References
Communications Physics (2025), DOI: https://doi.org/10.1038/s42005-025-02087-0