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
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.