lift and volume

[David]

I already know how this is going to end but I ask anyway.

if a 3 liter bottle with open end has x lift at ten meters how much lift does it have at 70 meters. yes I know it will take more gas because of the presure but the volume 3 liters will remain the same. As the bottle rises to the surface the gas will expand and escape from open end but will it still have same lift at depth.

David :-)

[Ivon]

It will have a lift of X.

Hope that helps.

[David]

Originally Posted by Ivon

It will have a lift of X.

Hope that helps.

I agree with you but spent a good half hour trying to prove the point but kept getting told I was wrong.

er Garf? Glock? want to add your views :-)

David

[nigelH]

Originally Posted by David

if a 3 liter bottle with open end has x lift at ten meters how much lift does it have at 70 meters. yes I know it will take more gas because of the presure but the volume 3 liters will remain the same. As the bottle rises to the surface the gas will expand and escape from open end but will it still have same lift at depth.

Well at 10m it will have 6L (surface) of air in it (weight 7.8gms) and at 50m 24L (weight 31.2gms) so there is a loss in lift of 23.4 gms.

But that's less than 1%, about the same as three £1 coins.

[Garf]

david . use all the physics you want but I'm telling you if you take a massive lungful of air at 3 metres you are on the surface. do the same thing at 50m and you hardly move. surely its as simple as the weight of water above you

[Mal Bridgeman]

If the problem is as Garf has described, then the issue is not about the air in your lungs on its own. If you breathe in at 3m then of course there will be a slight buoyancy shift but it will also trigger expansion of gas in the suit and wing which will trigger even more expansion and then you are on the surface.

At depth a slight rise in depth caused by breathing in will have virtually no effect on the other gas.

Pedant Nigel, does you calculation allow for any compression of the sea water at depth and does that makes any difference to the buoyancy as being the weight of fluid displaced?


Mal

[Kalahari Diver]

Or you just move a small amount which near the surface with large relative pressure changes pops you up?

David.

[David]

Originally Posted by Garf

david . use all the physics you want but I'm telling you if you take a massive lungful of air at 3 metres you are on the surface. do the same thing at 50m and you hardly move. surely its as simple as the weight of water above you

As I said mate your wrong :-)

David

[David]

Originally Posted by Mal Bridgeman

If the problem is as Garf has described, then the issue is not about the air in your lungs on its own. If you breathe in at 3m then of course there will be a slight buoyancy shift but it will also trigger expansion of gas in the suit and wing which will trigger even more expansion and then you are on the surface.

At depth a slight rise in depth caused by breathing in will have virtually no effect on the other gas.



Mal

Thanks Mal that clears it up nicely for me. as you say its not the gas in your lungs its the other air spaces not expanding at depth.

I just wish Garf was a better diver sometimes :-)

David

[David]

Originally Posted by nigelH

Well at 10m it will have 6L (surface) of air in it (weight 7.8gms) and at 50m 24L (weight 31.2gms) so there is a loss in lift of 23.4 gms.

But that's less than 1%, about the same as three £1 coins.

I wish I could work that out. Thanks Nigel

edit you did do that based on H at depth and 100% on surface dint you :-)

David