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It has been an item of folklore that a "pressurized" aircraft cabin, if punctured will force people through the aperture, a la Goldfinger. However, obviously the pressures inside the cabin (12 PSI) are nowhere near strong enough to move a human body (For reference, a can of coke is at about 40 PSI). To start throwing bodies out of windows, I would expect pressures over 100 PSI would be necessary.

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Nevertheless, despite this folklore, it has actually happened at least three times in real aircraft, most recently just this week in China.

So, I imagine the actual cause is not the pressure of the cabin, but the Bernoulli effect of air rushing past the window at 450 miles per hour. What kind of pressure differential will develop if air goes past a 20" x 12" window at 450 miles per hour?

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If the cabin pressure is about 12 psi and the outside pressure near zero, that means that a human body which would measure about 10 inches by 10 inches at the waist would experience 10 x 10 x 12 = 1200 pounds of force -- over half a ton -- when it was halfway out the window.

The head is roughly 5 x 7 inches, and would experience about 420 pounds of force if it got stuck in the window. More force than most people can deal with.

(Taking BowlOfRed's value for outside pressure, the net pressure differential would be 4 psi, and the waist and head forces would be 400 and 140 pounds respectively. Still pretty substantial.)

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  • $\begingroup$ Actual difference in a cruising airliner is about 50kPa (8psi or so). $\endgroup$ – BowlOfRed May 15 '18 at 23:12
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What kind of pressure differential will develop if air goes past a 20" x 12" window at 450 miles per hour?

The lowest that pressure can be is zero. So, certainly not less than that. Depending on altitude, the pressure will be low, but somewhat above zero.

Note there's no change in pressure from "air going past". To see that, the next time you're getting on a plane, look just forward of the jetway for something that looks like this:

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Those are the static ports from an Airbus A330, but other planes have similar ones. They're used to measure the static, ambient pressure of the air around the plane, which in turn is used in measuring altitude and other quantities. It doesn't matter whether the air is rushing past or not, the port samples the ambient pressure just like a broken window would.

Isn't this inconsistent with Bernoulli's principle? No. That's about the pressure and velocity of a single bit of air as it moves along a streamline. Here, by comparing air inside and outside, we're not comparing a single piece: Bernoulli's' principle doesn't apply.

It does apply for a bit of air that starts in front of the plane, goes by the port or window, and then goes past then end. It's always moving at the same speed, hence same pressure: Ports and windows sample that constant pressure.

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protected by Qmechanic May 16 '18 at 4:03

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