under pressure

Aeronautical science

I can’t go on an aeroplane without trying out a few little science tricks, and this one is a real favourite.

1 buy a bottle of water , while you sit for an hour in departures.

2 drink most of said water.

3 Once you are on the plane keep the bottle sealed, once at maximum altitude open the bottle. You’ll hear a distinct hiss as the air rushes out. The air pressure at ground level is much greater than at high altitude, so air escapes from the bottle to equalise the pressure.

4 Then reseal the bottle

My drink at 37,000 feet

5 Keep the bottle sealed, but watch it carefully as you make the approach for landing. As you descend the pressure around the bottle will increase, since you equalised the pressure in the bottle in flight it will be lower than the pressure on the ground.

You can get quite dramatic results.

my drink back on terra firma

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2 Responses to under pressure

  1. Ken Westgate says:

    The cabin in most passenger jets is actually pressurised to feel as though it is at an altitude of between 6000 and 9000 feet even though the aeroplane is at 37000 feet. This is because above 10-15000 feet the atmosphere is so thin that the body can struggle to get sufficient oxygen which is why climbers on high mountains usually use additional oxygen.

  2. 53ideas says:

    Thanks ken, you’re right of course. If the pressure in the cabin was as low as outside, the bottle would be squashed completely flat but you wouldn’t get then chance to see it

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