Eli5 why do airplanes have to fly so high?

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I was on a flight looking down at the cars on the highway and it hit me, like the higher you go the higher the radius is to cover the same distance as ground transportation. I’m sure there’s a cool reason and history. To make up for the extra fuel to get up that high and the extra miles added. Anyone? Does it have to do with less air pressure. And the efficiency aerodynamic wise? Or noise pollution? Visual pollution? I just always took it as a non ask, “We’re this high, cuz we’re in a plane. Duh”

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Anonymous 0 Comments

Air density drops significantly the higher you go. Less dense air means less resistance to moving, which means it’s easier to travel.

30000 ft is only 10 km, which is only 0.16% larger than the Earth’s radius. But air pressure (and density) is lower by ~75%, making it a lot easier to fly.

Additionally, the higher you fly, the less likely you are to bother residents with the super loud engines of the plane. It also gives you more room to avoid obstacles or other planes (shorter flights or smaller planes tend to fly lower).

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