EsquireFlyer

Hi FlyerTalk!

1. I've noticed over the years that when I carry bottles of contact fluid onto a plane, I hear a "whooshing" sound of gas if I open them onboard, or sometimes if I open them at my destination after landing. But it happens so fast that I can't tell whether gas goes in or out. I suspect it has to do with the cabin pressure being lower than atmospheric pressure at sea level..but can someone who knows more about science than I do tell me what's actually going on?

2. Similarly, when I carry bottled mouthwash in my checked bags, I find that it often overflows, even if the cap is closed tightly, if (and only if) the tamper-proof seal has been opened. For this reason, I pack the bottle in a ziploc bag, but it still spills within the bag (and the bag just keeps the spill from getting out). Can anyone tell me...if I want to reduce or prevent the spillage, should I squeeze the excess air out of the bottle before capping and packing it? Or should I let as much air into the bottle as possible before capping and packing it? Or something else?

Thanks!

alanh

The bottles all contain some air, which will be at ground-level air pressure.

The pressure inside the jet at altitude is lower, so the air inside the bottles expands. If not sealed tightly enough, it will leak and take some of the liquid with it.

Best thing is to squeeze the excess air out before traveling.

UnoriginalGuy

As an additional advantage, if you squeeze all of the air out, that often leaves additional space for the liquid to expand into so it won't break if completely full and with a poorly produced bottle/cap.

Frodosan

Typically liquids do not expand or contract with changes in pressure. They might slightly with changes in temperature or if frozen. This, of course, does not take into account any gases that might be dissolved as in carbonated drinks, etc. That is why hydraulic systems work as well as they do--and why you need to keep air out of them.

MisterNice

Do a google on Boyle's Law.

MisterNice

Flaflyer

You also have to watch out if you are on a long flight with meal service. The little ounce tubs of salad dressing with the foil lids are sealed at the factory near sea level. At altitude they are under pressure and the lid bows out like a dome. (along with the lids of the butter, jelly and juice tubs in the meal trays) Point it away from you when opening, unless you are one of those who like shaking your cola cans just before opening.

Next flight, make a Poor Man's Altimeter like I do. (there is not much else to do below 10,000 feet when your electronics must be turned off. ) The pressurized cabin altitude in a jet is about 6000 feet.

Carry an empty thin wall 500 ml disposable water bottle thru TSA or buy an overpriced on in the terminal and hope it does not get stolen in a TSA Gate Sweep. Use one with a regular screw top cap, not a pop up sippie type cap as they do not seal as tight. At max cruise altitude drink all the water and cap very securely. Make sure the bottle is normal shaped with no dents etc. Watch it as the plane descends. Around 6000 feet the bottle suddenly begins to crush. You will be surprised how much it crushes by the time you land. (assuming you are landing near sea level and not in Tibet or Bolivia)

tim1966

^ I thought I was the only person who did that! I think its the scientist in me, I love watching the bottle get crushed as you descend.

altaskier

Sea level atmospheric pressure is 14.7 pounds per square inch (psi) or 101 kiloPascal (kPa). At 7,000 feet altitude (typical of jetliner cabin pressure during cruise), it's about 11.3 psi or 78 kPa. Thus when you descend from cruise to land, your pressure has increased by (101-78)/78 or 30%.

I've also taken an empty bottle sealed at sea level down to 110 feet depth while scuba diving, where the pressure is more like 435 kPa, so that the ambient pressure more than triples. The bottle gets crushed some more, though of course since you're breathing gas and thus always adjusting to the pressure you don't feel crushed at all.

CPRich

One of those many little FF tips you pick up over the years. I always pierce the top with a tine of my fork before opening. Even opening it away from you can send salad dressing up against the seat in front of you.

Back when you could get bottles of water in flight I'd always finish it and then hold on to it through landing to watch it collapse. Then open it after landing to see it spring back.

LarryJ

Why would they take it from you during a gate sweep? Liquids purchased inside of security are allowed on the airplane.

The aircraft's altitude will have nothing to do with it. The bottle will begin to crush as soon as the pressurization system begins to descend the cabin which is usually as soon as the aircraft begins it's initial descent.

EsquireFlyer

Wow! Thanks for the advice and DIY experiment tips, everyone!!