Pressure ≠ Gravity

For pretty much as long as man has lived we have dreamed of touching the sky. From the legend of Icarus to the flight to the moon, man has always striven to fly higher and better. My wife, though, hates flying. Even so she and I do our fair share of it as we flit from here to there and back again. That's why a question she asked me recently caused me to shake my head in defeat.

"So, if an airplane has a pressurized cabin, and we were to turn upside down, would the passengers even know?"

Now, if you know anything about how gravity works, and I'm assuming you do, then you will know that yes, gravity still functions even if the air is pressurized. Elizabeth had just assumed that when the cabin air is pressurized the pressure would be great enough to glue the passengers to their seats.

The reason planes pressurize there cabins actually has nothing to do with keeping passengers seated, though it has everything to do with keeping them comfortable. And, you know, alive. Humans need air to be at a certain density for us to be able to get enough oxygen from it to survive when we are breathing, and air over a certain elevation becomes too thin for us to breathe. If you've ever been at the top of a mountain you may have noticed a feeling of being out of breath, or perhaps you've experienced altitude sickness. This is due to the lowered level of oxygen being absorbed with each breath. In order to keep air at a comfortably breathable density, airplanes are designed to push extra air into the cabin where passengers sit. This increases the pressure, which gives rise to the name "pressurized".

If the air was pressurized to such a point that humans wouldn't fall when the plane is turned upside down, we'd have a whole other set of problems to deal with. Namely, the air would be slightly thicker than water.

Now if I just understood the other set of problems having to do with flying upside down......

Thanks to xkcd.com for the comic above.