If you're a seasoned traveler, then you may recall a time when square-shaped airplane windows were the norm.
But nowadays, plane windows are round. And it turns out there's a VERY important reason for the change.
As airplane models became more modern and capable of flying at higher altitudes, the pressure difference between the cabin and outside air became greater, this video from Real Engineering explains. The pressure difference causes the plane to very slightly expand, which creates stress. The window shape becomes crucial in preventing the level of stress from raising so high that is cracks.
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