Under Pressure 1
This is what my water bottle from the plane looked like when I got back to Cape Town, after my month away in the UK.
Generally speaking, a large plane flying at high altitudes, like my Boeing 747-400 cruising at 12,200 m (40,000 ft), has to pressurise the air inside the cabin, because the outside air at that altitude is at a much lower pressure than is good for you!
Even so, they don’t quite match the pressures you might experience down on the ground; cabin pressure is usually set to that which you would experience at 1500 m to 2440 m (5000 ft to 8000 ft).
Under Pressure 2
When I got back to my house and took out my water bottle (that had been opened and resealed while up in the air on the plane) the increase in atmospheric pressure here in Cape Town at sea level was enough to squish the plastic bottle.
In fact, the pressure that day, according to the barometer in my lounge, was a whopping 104 kPa (780 mm Hg).
No wonder I had a headache!
And how could I have a post with this title and not mention David Bowie and Queen Under Pressure.
post script: It has taken me a while (9 drafts) to put this post together, with all the reference material. And though I know that a post like this will not be generally popular, I find it interesting.
In case you’re also interested, here are a whole lot of links so you can read up on this subject. You’re welcome!
cabin pressure versus air pressure and cabin altitude
Physics experiment of a plastic bottle on a plane.
Table of atmospheric pressure at different altitudes.
Diagram of how cold it is at different altitudes.
Health advice before you travel by air.