Water Pressure and Internal (Air) Pressure

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Discussion Overview

The discussion centers around the effects of external water pressure and internal air pressure on tubes submerged at significant depths. Participants explore how these pressures interact, particularly focusing on the implications of varying internal pressures on the forces experienced by the tubes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions whether a tube with lower internal air pressure experiences a greater relative force from external water pressure, suggesting a potential effect of pressure equalization.
  • Another participant confirms that the net force on the tube is proportional to the pressure difference between the inside and outside.
  • A participant raises a question about the origin of the force, inquiring if it is derived from the combination of water and air pressure or if other factors are involved.
  • It is noted that if the tube is flexible, the pressure on the inside surface may also equal the external water pressure, complicating the pressure dynamics.
  • A participant introduces the concept of hoop stress, explaining that it supports the pressure difference between the inside and outside of the tube.
  • Another participant expresses curiosity about the potential significance of other forces, such as buoyant forces, while concluding that water and air pressure seem to be the major forces at play.

Areas of Agreement / Disagreement

Participants generally agree on the role of water and air pressure in influencing the forces on the tubes, but there are differing views on the implications of internal pressure variations and the potential significance of other forces.

Contextual Notes

There are assumptions regarding the impermeability of the tube's microstructure and its strength to withstand external pressures, which may affect the discussion's conclusions.

ipen
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If you have, say, two tubes of different internal pressures submerged to a given depth (for sake of the example, let's just say 1,000M underwater or 100 ATM), will the smaller internal air pressure tube experience a greater relative force from the water pressure? The water pressure on both tubes should be the same from the outside, but is there an additional effect where water tries to equalize the pressure at a greater magnitude of force on the tube with less internal air pressure? I guess an extreme, clearer hypothetical comparison would be between a tube with a vacuum on the inside compared with a tube with air pressure equal to 99.99% of the water pressure on the inside. I'm also assuming that the tube's microstructure is impermeable to water, and that the tube is strong enough to withstand the water pressure at the given depth.

Thanks in advance!
 
Last edited:
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ipen said:
is there an additional effect where water tries to equalize the pressure at a greater magnitude of force on the tube with less internal air pressure?

Yes. The net force is proportional to the pressure difference.

If the tube distorts in any way that changes the volume then the pressure inside can change meaning the pressure differential and the net force will also change.
 
Is this force derived from the water and air pressure combo, or something else?
 
What else could it be?
 
The pressure on the outside surface of the tube is the water pressure. If the tube is flexible, the pressure on the inside surface is also the water pressure.
 
The tension or compression stress in the circumferential direction (i.e., the so called hoop stress) supports the difference in pressure between the inside and the outside of the tube. So the tube itself is part of what is happening.

Chet
 
Thanks for the answers. :)

I was wondering if there were other forces, maybe even buoyant forces that would be significant.

But from what I can tell, it seems like the major ones are water and air pressure.
 

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