Techno-geek question: If a cup is pushed under water with air inside the bell...

[BlondGirl]

Will that eventually fill with water or will the air continue to maintain that space indefinately?

I was assuming not, since air is absoarbed in water and combined with evaporation, these would fill the cavity.
But I could be just rationalizing out what I would like to believe.
Anybody smarter than me got an answer?

I was thinking of underwater caves and sunken boats too.

 

[Phoenyx]

Will that eventually fill with water or will the air continue to maintain that space indefinately?

I was assuming not, since air is absoarbed in water and combined with evaporation, these would fill the cavity.
But I could be just rationalizing out what I would like to believe.
Anybody smarter than me got an answer?

I was thinking of underwater caves and sunken boats too.

Depends on how deep under water..
Evetually high water pressure might force its way in...

Else I see it staying the same.

 

[Thumper]

It is absorbed only if the pressure is high enough. Even then only the oxygen is readily absorbed.

Go deep enough and it won't matter the cup will be crushed.

 

[Shy Tall Guy]

The air would be present indefinitely - some could be absorbed into the water, but not much. I believe that air pockets have been found in sunken boats, etc. long after they sank.

 

[Chuckus]

Re: Re: Techno-geek question: If a cup is pushed under water with air inside the bell...

Depends on how deep under water..
Evetually high water pressure might force its way in...

Else I see it staying the same.

What he said.

 

[seXieleXie]

Will that eventually fill with water or will the air continue to maintain that space indefinately?

I was assuming not, since air is absoarbed in water and combined with evaporation, these would fill the cavity.
But I could be just rationalizing out what I would like to believe.
Anybody smarter than me got an answer?

I was thinking of underwater caves and sunken boats too.

the air will maintain a smaller space under water because now there is X feet of water pressing down on it, rather than the column of air which makes up the atmosphere. and of course there is water pressing up on it from below as well.

a little bit of the air would dissolve under the pressure, but there would also be water vapor present mixed with the air.

i'm not sure what you mean by evaporation in terms of the amount of air present, evaporation is the change in state from liquid to gas so if the air is aready gaseous then it won't have any effect.

so, the air would stay if the cup is rigid enough and doesn't tip.

 

[BlondGirl]

the evap I was referring to was the water vapor "sweating" on the inside of the container.
I assume that eventually the air "pocket" would be absoarbed in the constantly moving water. I cannot see why it would not. I wonder if I could experiement with a heavy glass coffee cup in the fish tank to see what would happen.
(Presuming that I have a fish tank, of course.)

 

[Fly_On_Wall]

Re: Re: Techno-geek question: If a cup is pushed under water with air inside the bell...

The air would be present indefinitely - some could be absorbed into the water, but not much. I believe that air pockets have been found in sunken boats, etc. long after they sank.

yes but if long enough those air pockets have little trace of oxygen, and is more nitrogen based. so if you were diveing and lookint for that area as a safe rest cause somthing is wrong. the air would not be breathable.

 

[seXieleXie]

the evap I was referring to was the water vapor "sweating" on the inside of the container.
I assume that eventually the air "pocket" would be absoarbed in the constantly moving water. I cannot see why it would not. I wonder if I could experiement with a heavy glass coffee cup in the fish tank to see what would happen.
(Presuming that I have a fish tank, of course.)

once the system's temperature came back to equalibrium after introducing the new element (read: the cup/air) it wouldn't sweat any more.

 

[BlondGirl]

Why not? Why would the water that is in the lowest parts of the bell not experience evaporation? Why would that not float up and drip off the insides of the container?

And why would the bell contain nitrogen?

 

[RhumbRunner13]

B girl,

The air in the glass rapidly reaches 100% humidity, at which point all evaporation ceases. Any condensation would require condensation nuclei and the resultant drops would simply drip back into the water below lowering the humidity in the glass.....in other word a state of stasis would be reached.

Fun question.

 

[Fly_On_Wall]

Why not? Why would the water that is in the lowest parts of the bell not experience evaporation? Why would that not float up and drip off the insides of the container?

And why would the bell contain nitrogen?

wait do you mean a fully submurged cup? or one that has the ouslide water level half way up so it's still expose to the air?

if it's still expose and it was really hot the water cold then yes eventualy the water under the cupp will be pulled up inside like when you have plants covered in plastic the plastic inside get's wet.
the cup would get wet, and as water is being pulled up into the cup the air will seap out to make room for the new mass.

 

[BlondGirl]

Explain the nitrogen thing. I think I might have figured it out, but I could be wrong and am not sure if I can put my thoughts in a coherent form yet.

 

[seXieleXie]

just to make sure we're on the same page... i drew a little pic (in paint, so it sucks) of what i think you're talking about. is this about right BG?

 

[seXieleXie]

air is somethingl ike 80% nitrogen

 

[Fly_On_Wall]

Explain the nitrogen thing. I think I might have figured it out, but I could be wrong and am not sure if I can put my thoughts in a coherent form yet.

if it were in an underground cavern very deep.

the air is made up of oxygen, hydrogen, nitrogen, helium and other minute gasses.

if it were that deep the oxygen and hydrogen would eventualy react to form water cause of how cold it is at low temperatures. not all of it would though I don't think... this would make the nitrogen persentage of the air alote higher.so lets say there are only the three gases and equil parts of oxygen hydrogen and nitrogen. therfore 33.3% of each
if you remove half the oxygen and hydrogen now there is only
16.5% of the oxygen left 16.5 of the hydrogen and still 33.3% of the nitrogen so the air would be unbreathable. but if this were a cave, the nitrogen would seep into the cavern walls. so let's say it's a boat instead, less room for the nitrogen to escape. (also in a cavern any gas will absorb into the wall and try to escape the ocean floor cause well as my physics teacher use to say. gas likes to be in the air where you can smell it lol.)

it's been awhile since i've taken physics so some of what I said may be mixed up a bit.

 

[BlondGirl]

just to make sure we're on the same page... i drew a little pic (in paint, so it sucks) of what i think you're talking about. is this about right BG?

Yes, that is roughly the visual I had too.

Hell, while we are discussing wierd questions, do fish (and other underwater creatures) fart? Perhaps the bell could contain a volume of methane as well.

 

[Texan]

Oh hell… I’m bored and I can’t resist.

First, the air in the cup will remain in the cup FOREVER. However, there are some things that can affect the nature of the air and the space it occupies.

The air will never dissolve in the water. It takes either heat or pressure to force the oxygen atoms to “bind” with spare hydrogen atoms in the water to create a hydroxide. To be more specific, at 68F, (the temp cited for most comparisons) it would take 189PSI to force the oxygen out of the air. This would require a pressure of about 7 atmospheres or a depth of around 210 feet. To make the problem more complicated, the temperature of the water at 210 feet would be much colder than 68F, therefore it would require an even greater depth to force the oxygen out of the water. (I don’t know the temperature of water at different depths.)

The space the air would occupy would decrease as the pressure (depth) increased. The amount of decreased space is a curve that begins at a reduction of 7% of air volume for each atmosphere (30 feet) of depth. The greater the depth, the less the decrease in volume.

This is the simple explanation. The more complete explanation would include the possible binding of other components in the air with possible dissolved salts in the water, the variable rigidity of the cup and the increase in the temperature of the air as the pressure increases.

I remember the days when this stuff was fun….. now balancing a check book on a joint account is a challenge….

 

[Fly_On_Wall]

thanks texan, that's what I was trying to hit on with the underwater cavern thing.

couldn't word it properly.

 

[Unclebill]

Originally posted by Thumper
It is absorbed only if the pressure is high enough. Even then only the oxygen is readily absorbed.

Go deep enough and it won't matter the cup will be crushed.

Actually, no matter how deep its taken, the cup will not be crushed. The gas inside is compressed to the same pressure as the water surface against it.

As Texan stated, the volume of gas would decrease as depth increased, but since the internal and external presure on the cup is balanced, it would never crush.

On the other hand, if you took a sealed container down, it would eventually be crushed since the internal pressure would remain unchanged until it reached crush depth.

Ask a submariner about the "crush depth" concept. They take it seriously.