Pressure Depth in a Cave

[Melicertes]

take a weigh scale and stand in a doorway. Does it weigh the house?

I detect a very dry sense of humor Kinda ironic for a scuba diver

 

[duckster3d]

I know that, but does the earth between the atmosphere and the submerged cave have any role of applying pressure on the water column?

NO

though Alert mag, had an interesting article on water pressure.

if you put a tube down into the water and sealed off the top and hoisted it up out of the water. the pressure would drop at the top of the tube to 0 ata. and the total height of the water that could be held up would be 33'. if a diver ascended into the tube and swam up the tube to 8.9 feet above the outside water level he would feel the decrease in pressure to the effect of being at 8000 feet above sea level. go to the surface of this and you've ascended to 100,000 feet above sea level. talk about getting bent.

 

[Melicertes]

A.............................Ground Level................................ E
*..............................................................................*..
..*..............................33' C.....................................*...
....*....................... * * * * * *..............................*.....
.......*..................*..................*.........................*........
..........* 99' B....*......................*...99" D.........*..........
.............* * * *............................... * * * * * *............

Points A and E are 1 ATA

Points B and D are 4 ATA

What is the ATA of C (assuming the water course "*" is open only at A and E) -- 2 or 4?

To my knowledge the pressure at point C will be 4ATA. Hydrostatic pressure is exerted in all directions since it is not a vector. The 4ATA pressure exerted by the water between points A&B and E&D will exert 4 ATA pressure respectively up and into the channels between B&D. If C was exposed to atmospheric pressure above it, it would be 2ATA, but since it's a closed system it'll be 4ATA

I'm no engineer, but that's how I understand the physics. Anybody got some engineering background with some fluid dynamics knowledge?

 

[Dan Gibson]

If point C was exposed to atmospheric pressure above it, the water level would not be 33' below A & E.

To my knowledge the pressure at point C will be 4ATA. Hydrostatic pressure is exerted in all directions since it is not a vector. The 4ATA pressure exerted by the water between points A&B and E&D will exert 4 ATA pressure respectively up and into the channels between B&D. If C was exposed to atmospheric pressure above it, it would be 2ATA, but since it's a closed system it'll be 4ATA

I'm no engineer, but that's how I understand the physics. Anybody got some engineering background with some fluid dynamics knowledge?

 

[limeyx]

I detect a very dry sense of humor Kinda ironic for a scuba diver

Jeff's so dry, he's all cracked up!

 

[Blackwood]

To my knowledge the pressure at point C will be 4ATA. Hydrostatic pressure is exerted in all directions since it is not a vector. The 4ATA pressure exerted by the water between points A&B and E&D will exert 4 ATA pressure respectively up and into the channels between B&D. If C was exposed to atmospheric pressure above it, it would be 2ATA, but since it's a closed system it'll be 4ATA

I'm no engineer, but that's how I understand the physics. Anybody got some engineering background with some fluid dynamics knowledge?

No fluid dynamics here. We're assuming hydrostatic conditions.

Take the cave away. In a 99 foot deep section of ocean, the 4ATA at the sea floor doesn't raise the pressure of the water 66 feet above it, right?

Dropping a tube (or cave) into the water won't make a difference.

The ambient pressure in the water at a given depth is the force it distributes over some area. That's a function of the weight of the water on top (relative to gravity) of said area.

 

[Thalassamania]

take a weigh scale and stand in a doorway. Does it weigh the house?

That was REALLY GOOD!!!!

 

[Blackwood]

That was REALLY GOOD!!!!

Yah. One of the funniest posts I've seen.

 

[Melicertes]

If point C was exposed to atmospheric pressure above it, the water level would not be 33' below A & E.

I do not agree, if the area between A&E were excavated to expose C to the surface, and thus the atmosphere, the 4ATA water pressure between A&B and E&D respectively would force water out of the newly exposed area C, and probably flood the excavated basin; the water levels in A&B and E&D would drop to the same level as the water level above the now flooded area C thereby decreasing the pressure at B and D from 4ATA to somewhere slightly over 2ATA depending on the depth of the water above C. The water surface above C would then be at 1ATA.

 

[Melicertes]

No fluid dynamics here. We're assuming hydrostatic conditions.

Take the cave away. In a 99 foot deep section of ocean, the 4ATA at the sea floor doesn't raise the pressure of the water 66 feet above it, right?

Dropping a tube (or cave) into the water won't make a difference.

The ambient pressure in the water at a given depth is the force it distributes over some area. That's a function of the weight of the water on top (relative to gravity) of said area.

This is correct but the problem with the analogy is that in open water conditions you have C exposed to atmospheric pressure and in the cave example it is not - the cavern roof prevents the water pressure at C to equalize relative to atmospheric pressure.

Check out the following link and pay attention to the second paragraph: "Pascal's law states that when there is an increase in pressure at any point in a confined fluid, there is an equal increase at every other point in the container."

I'd say B and D are subjected to increased pressure relative to A and E, and since it's a closed container even if we just prefer to call it a cave, weeeell....