weird anti-physics on Mt Buffalo

[slparker]

I went up to the snow yesterday and packed an old collapsible water bottle 3/4 full of water that I shoved in the car.

After skiing I retrieved the water bottle from the car to find that the water bottle had collapsed inwards - it reinflated when I opened the seal...

Now this shouldn't happen... I went from a place of high ambient pressure at 200m ASA to a place of lower ambient air pressure at 1700m ASA - the bottle, if anything, should have been as tight as a drum. It hadn't been opened prior to cracking it at the top. I thought that it may have been the cooler temperature but it was in the car sitting in the sun and the bottle, whilst cool, was in no way ultra-cold.

the aluminium bottle that I opened whilst skiing let out the expected hiss of escaping pressure as the high pressure air left the bottle.

i am thoroughly confused as to how this could happen.

[Earwig]

As water cools it takes up less space - it shrinks. A litre of water has it's maximum density (takes up the least space) at 4 degrees, than starts to expand again. The water must have cooled enough to shrink and suck the bottle inwards.

[neilmny]

Hmmm.....I think you may have passed through the matrix......

There would have to have been a lot of shrinkage in volume to collapse the bottle specially when 1/4 of it was air which would expand a fair bit.
Tap water would be fairly cold at this time of year so dropping to 4C probably wouldn't be a huge change in temperature.
Very interesting event slparker.

[Moondog55]

I think it's a pumping effect
Because of the way the screw top fits air can escape more easily than it can get in, so if it was warm in the car and the air inside the bottle warmed up it can get out but if the pressure on the outside becomes higher then that pressure pushing down on the top makes the seal more effective and air can't get back in as easily.
A few cycles like that and I see no problem with what you describe happening
But I could be wrong

[Hallu]

As water cools it takes up less space - it shrinks. A litre of water has it's maximum density (takes up the least space) at 4 degrees, than starts to expand again. The water must have cooled enough to shrink and suck the bottle inwards.

The volume difference from 20° to 4° is only a fraction of a per cent, this is not the explaination.

As for what slparker says : "I went from a place of high ambient pressure at 200m ASA to a place of lower ambient air pressure at 1700m ASA - the bottle, if anything, should have been as tight as a drum." It's wrong as well. Less pressure on the outside yes, but inside the bottle it hasn't changed, it's a container. So it's more likely there was a leak, and the pressure wanted to equalize by making the air escape, hence collapsing the bottle.

[neilmny]

As water cools it takes up less space - it shrinks. A litre of water has it's maximum density (takes up the least space) at 4 degrees, than starts to expand again. The water must have cooled enough to shrink and suck the bottle inwards.

The volume difference from 20° to 4° is only a fraction of a per cent, this is not the explaination.

As for what slparker says : "I went from a place of high ambient pressure at 200m ASA to a place of lower ambient air pressure at 1700m ASA - the bottle, if anything, should have been as tight as a drum." It's wrong as well. Less pressure on the outside yes, but inside the bottle it hasn't changed, it's a container. So it's more likely there was a leak, and the pressure wanted to equalize by making the air escape, hence collapsing the bottle.

A soft container would be "blown up" as altitude increased by the pressure inside trying to equalise with the lower pressure outside. (Take a look at potato crisp packets at a ski resort)
If air was able to escape, but not water (I don't see this is possible) it could only be to the extent that inside and outside air pressures were equal and it would not crush the container, the container would only take on the original form it had at low altitude. The outside pressure would have to exceed the inside pressure to crush the container or the water volume would have to shrink.

[Travis22]

Charles's Law.

When you stopped and parked the car and left it up there the car naturally cooled down along with everything in it. The air in the bottle cooled down faster then the air outside of the bottle, so the air inside the bottle is at a lower pressure to the air outside of the bottle, thus it caves in a bit.

I see the same thing all of the time in my wifes car, she always drinks 600ml bottled water and bottles left overnight in the car partially drunk do the same thing.

Travis.

[DaveNoble]

The water (a liquid) may contract - but not very much at all. But air (a gas) does expand and contract a lot depending on temperature.

One factor is the changing air pressure outside the bottle. You would expect this to go down with an increase in altitude and then this would lead to the air remaining in the bottle to have relatively higher pressure so the bottle would expand. But it is also possible for the local air pressure to increase -eg a big high pressure cell may have zoomed in.

The other factor is the air in the bottle cooling down - the air then takes up less space - and this would lead to the bottle contracting since it is flexible. Note - The air in the bottle cools down at about the same rate as the air outside it - the plastic of the bottle will not make that much difference to the cooling rate and the air in the metal bottle will also cool and contract - but its bottle is rigid - so it cannot contract. So the air pressure inside will go down, and hence the hiss.....

In this case, it looks like the second factor was more important.

Dave

[neilmny]

Another thought .......the bottle stretched in the sun, some heat, UV.
A temperature change of 37.8C (310.9K) will alter the volume of air by 22%

[slparker]

Another thought .......the bottle stretched in the sun, some heat, UV.
A temperature change of 37.8C (310.9K) will alter the volume of air by 22%

it's possible - the bottle was in my bag in the car so wasn't exposed to the sun directly. It wasn't hot in the car - it was probably around the teens. If it did get hot then the bottle would have expanded... not contracted,

i am thoroughly mystified. I would accept some local very high air pressure with a high moving in but that means that the ambient pressure would have to be higher than that at 200m ASA which I doubt.

[slparker]

Charles's Law.

When you stopped and parked the car and left it up there the car naturally cooled down along with everything in it. The air in the bottle cooled down faster then the air outside of the bottle, so the air inside the bottle is at a lower pressure to the air outside of the bottle, thus it caves in a bit.

I see the same thing all of the time in my wifes car, she always drinks 600ml bottled water and bottles left overnight in the car partially drunk do the same thing.

Travis.

I don't think that it is possible for the air in the bottle to cool down faster than the air around it - second law of thermodynamics and all that. I accept that when the water, and the air surrounding it, cooled down then the air pressure inside the vessel drops but that drop would have to be sufficient to overcome the relative net gain in pressure (trapped at 200m ASA) above that of ambient pressure (@1700m ASA).

It wasn't that cold in the car....

[GBW]

I think it's a pumping effect
Because of the way the screw top fits air can escape more easily than it can get in, so if it was warm in the car and the air inside the bottle warmed up it can get out but if the pressure on the outside becomes higher then that pressure pushing down on the top makes the seal more effective and air can't get back in as easily.
A few cycles like that and I see no problem with what you describe happening
But I could be wrong

I agree with moondogs theory...the one-way valve...especially with a screw top...some of the air in the bottle escaped as altitude increased then cooling caused a collapse of the bottle.

[Earwig]

I think this needs further research. We should all partially fill a water bottle and go skiing for the day.

[neilmny]

I think this needs further research. We should all partially fill a water bottle and go skiing for the day.

Is it OK if I just go skiing for the day

[Chezza]

Charles's Law.

When you stopped and parked the car and left it up there the car naturally cooled down along with everything in it. The air in the bottle cooled down faster then the air outside of the bottle, so the air inside the bottle is at a lower pressure to the air outside of the bottle, thus it caves in a bit.

I see the same thing all of the time in my wifes car, she always drinks 600ml bottled water and bottles left overnight in the car partially drunk do the same thing.

Travis.

I don't think that it is possible for the air in the bottle to cool down faster than the air around it - second law of thermodynamics and all that. I accept that when the water, and the air surrounding it, cooled down then the air pressure inside the vessel drops but that drop would have to be sufficient to overcome the relative net gain in pressure (trapped at 200m ASA) above that of ambient pressure (@1700m ASA).

It wasn't that cold in the car....

I'm with you, I would have expected the air pressure in the bottle to be slightly higher than its surrounds at altitude.

I checked BOM data for evidence of a sudden change in atmospheric pressure, but that day saw fairly constant pressure.

It is possible that the plastic in your bottle is selectively permeable to oxygen (common in some plastics) or some other atmospheric component. The partial pressure of these gasses would be lower at elevation, resulting in diffusion out of the bottle. I have no idea how fast this process would be.

This calls for repeat experiments, ideally with an instrumented bottle and an instrumented car. Do you happen to have a datalogger lying around?

[slparker]

I'm with you, I would have expected the air pressure in the bottle to be slightly higher than its surrounds at altitude.


Do you happen to have a datalogger lying around?

To be pedantic, pressure equalised (hence the crushed bottle) - air density is the issue.

I am trying to think of a one way valve scenario like moondog suggested - but that still doesn't work because the air density in the air space of the bottle was less than ambient pressure at 1700m - because the bottle expanded on opening the seal.

This suggests that the bottle was exposed to lower pressure than that at 1700m and resealed. But I definitely closed the bottle at 200m ASA and opened it at 1700 m and Cresta Valley is the highest point of the road before ascending the horn access road.

My last hypothesis is that water was squeezed out of the bottle (perhaps the snowchain case fell on the bottle) whilst the bottle was upside down and water left the bottle but air did not leave because of the water seal. UNfortunately i did not notice my gear being wet... nor was the cap loose. i am still mystified. i am going to send the problem to a physics lecturer.

[South_Aussie_Hiker]

A weather related barometric pressure change is not significant enough to overcome the altitude change so this theory should be disregarded. Even a sudden and very strong change in atmospheric pressure would only change the pressure about 3%, where as 200m-1700m ascent would change it about 15%.

Dave Noble and Moondog are correct.
1. You assumed that the hiss from the aluminium bottle was air escaping - it MAY have been the opposite (but most likely wasn't)
2. It's quite likely the bottle seal on the collapsible bottle equalised allowing air out during the ascent. Then on reaching 1700m, the water and air in the bottle has slowly cooled. The cooler air has contracted the bottle inwards. The aluminium bottle probably has a much better seal which didn't allow equalisation during ascent, or if in the unlikely event it too allowed equalisation during ascent, then in too cooled down and actually hissed air IN as you unscrewed it.

[neilmny]

Hmmm.....that would be a SSIH then wouldn't it.