Air pressure at water depth and buoyancy

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Discussion Overview

The discussion revolves around the buoyancy of a platform designed to float at varying water depths from 0 to 100 meters, specifically addressing the effects of air pressure on the volume of air used for buoyancy in a rigid container. Participants explore the implications of water depth on buoyancy and the structural integrity of the container under pressure.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the volume of air for buoyancy should be calculated at atmospheric pressure or at 100 meters depth, suggesting that using the latter might result in a greater net upward force.
  • Another participant inquires about the compressibility of the container, which leads to clarification that the container is rigid.
  • A participant states that in a rigid container, the buoyancy force is determined by the weight of the container minus the weight of the water displaced, based on the volume of the container.
  • It is proposed that the air volume needed to float the platform can be based on sea level conditions since the air will not compress in a rigid container.
  • Concerns are raised regarding the structural integrity of the container at 100 meters depth, with a participant noting that the pressure could lead to implosion.
  • Alternative suggestions include using gas or oil to fill the container, as these substances are lighter than water and would not compress, or using wood for flotation instead.

Areas of Agreement / Disagreement

Participants express differing views on the appropriate volume of air to use for buoyancy, with some advocating for calculations based on sea level and others considering the effects of depth. The discussion remains unresolved regarding the best approach to ensure buoyancy while maintaining container integrity under pressure.

Contextual Notes

Limitations include the assumption that the rigid container will not compress, and the potential for structural failure at depth due to high pressure. The discussion does not resolve the implications of using different materials for buoyancy.

malek340
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I'm doing a project that requires a platform that is able to float up and down a water depth of 0-100m. It'll be pulled down by a fishing line. I'm currently using air as buoyant. This air will be trapped in a container. However there is air pressure at a certain water depth. The air will certainly be compressed at a 100m water depth. What volume of the air should i use? Is it the volume of air needed to float the platform at atmospheric pressure(sea level) or at the 100 water depth.

If i were to use the volume of air to float the platform at 100m, wouldn't the net upward force(buoyancy force against the weight of object) acting on the platform be greater?
 
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Is your container compressible like a balloon or is it rigid?
 
Yup it's quite rigid.
 
Then the bouyancy force is the weight of the container minus the weight of the water displaced (the volume of the container times the weight density of water).
 
If it's rigid, then you can use the air needed to float the platform at sea level. In a rigid container, the air will not compress.

However, you must make the container quite strong. Pressure at 100m is about 160psi, or 1.10 Mpa. There's a good chance your container will just implode.

Alternatively, you might consider filling the container with gas or oil. These are lighter than water and will provide bouyancy, but are incopressable and will not get crushed or change volume. Or you could just use wood for floatation.
 

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