And why you won't see sharp edges inside a plane, period.
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While boarding an airplane, you might not notice much. Maybe you'll glance at your ticket, look to find your seat number, and reach down to hoist your bag into a tight overhead bin before wrestling your way to your seat, where you'll let out a little huff before buckling in. After that mini chaos is over, you can finally look up and take in your surroundings. And that's when it could hit you: Everything on this plane is, in some way, round.

From armrests to tray tables, television screens to windows, there are no sharp edges on a plane. And that's for a very good reason.

Windows Of Airplane
Credit: Daniil Yakubenko/Getty Images

"Sharp edges hurt elbows, knees, hips… or any part of the body that they come into contact with," Anthony Harcup, senior director at design house Teague, a design firm that has worked with Boeing for over 75 years, told DMarge in a December interview. He explained, the rounding of edges is done for "delethalization," a design principle that "ensures that when subjected to Murphy's law, a passenger can't hurt themselves on any part of the aircraft seat."

Furthermore, Harcup notes, it's not just for our protection, but for the plane's as well. "Whether a part is molded, machined and painted, or covered in laminate, the finish is far more likely to get stress fractures or have the finish wear off at the high-point when manufactured with sharp edges," he added.

Beyond looking good, rounded windows in particular keep us far safer in the sky than windows with sharp edges would.

As the Real Engineering YouTube explains in the above video, as passenger planes became more popular in the 1950s, airlines began to fly their aircraft at higher altitudes, which would allow for them to save money thanks to the thinner air, which creates less drag and a more comfortable ride with less turbulence. However, at the time, the airlines didn't make the correct design changes to ensure passenger safety. They left in the fatal flaw of square windows, which created stress spots due to the pressure difference inside and outside the plane.

"When a material changes shapes like this, stress is created in the material," the channel explains, "eventually the stress can rise so high that the material breaks."

This is exactly what happened in 1953 and 1954 when two planes disintegrated mid-air due to square windows. Don't worry, we've come a long way in both airplane safety and design since then. But maybe next time you step on a plane, say a little "thank you" to designers and engineers for those nice round edges so you literally and figuratively won't hit any snags in the air.