How can I calculate the force and pressure on an object submerged in water?

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Discussion Overview

The discussion revolves around calculating the force and pressure on an object submerged in water, specifically focusing on buoyancy and the effects of water pressure at depth. Participants explore the principles of buoyancy, the impact of pressure on submerged objects, and the equations relevant to these concepts.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions how to calculate the force and pressure on a submerged object, providing specific parameters (mass of 20kg, volume of 1m3, and depth of 50m).
  • Another participant asserts that buoyancy remains constant at different depths as it depends on the volume of fluid displaced, which does not change with depth, while acknowledging that pressure increases with depth.
  • A different viewpoint is introduced regarding the compression of air within the object at depth, suggesting that buoyancy decreases as the volume of air is reduced under pressure.
  • Further clarification is provided that if the object maintains its volume of 1m3, it will displace the same mass of water regardless of depth, but if the object is compressed, its buoyancy would decrease.
  • One participant emphasizes the importance of buoyancy for scuba divers, noting that as they descend, they experience a loss of buoyancy, which affects their rate of descent.
  • A later reply seeks to focus on the actual upward force the buoy can exert, indicating that buoyant force can be calculated as the difference between the mass of water displaced and the mass of the object.
  • Another participant provides a calculation for the buoyant force, equating it to the weight of the displaced water and contrasting it with the weight of the object to determine the net force required to keep the object submerged.

Areas of Agreement / Disagreement

Participants express differing views on the effects of pressure on buoyancy and the calculations involved. While some agree on the principles of buoyancy, there is no consensus on the implications of pressure and the calculations for force and pressure on the submerged object.

Contextual Notes

Participants reference various assumptions regarding the behavior of submerged objects, including the effects of pressure on volume and buoyancy, which may depend on specific conditions not fully explored in the discussion.

ML
I was wondering a couple of things about an object of mass 20kg and volume 1m3 being submerged under say 50 metres of water. Basically I'm looking for the two equations that would help me figure out the force and pressure surrounding the object to make it rise.

similar to that of a fishermans' bhoy being submerged.
 
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The bouyancy should be the same at 50m as it is at the surface, since bouyancy is dependent on the mass of the fluid displaced. Although the pressure being exerted on the sides of the object would be much greater, this would be equally true from all directions, so the extra force pushing up from underneath is the same as the extra force pushing down from above.

But so long as the object remains 1m3 in volume, it will displace 1m3 of water, and the mass of that water will be the same at depth as it is on the surface because despite the great pressure, water doesn't compress (well, not much, anyhow). So the object displaces 1,000kg of water at any depth.
 
Lurch, have you ever been scuba diving? What you find happens is that the air in the object gets compressed due to the pressure and your buoyancy decreases with depth. IIRC you find that the air in an object will occupy 10/(D + 10) times volume than it will at the surface (where D is the depth).
 
Quite right, jc. You don't mind if I call you that, do you? Makes me feel like I'm in the movie business.

Anyways, that's why I made a point of it to mention that the object's bouyancy remains the same "So long as the object remains 1m3 in volume". But it's good to reinforce the pointthat if the object gets shrunk by the pressure, it will of course become less buoyant.
 
It's just that buoyancy is important to scuba divers (I got my advanced PADI qualification this Summer) and when you start to descend you find the deeper you go the faster you go down as you lose buoyancy.
 
.

I appreciate these replies but i was focusing more on the actual force that the buoy would be capable of pulling upwards or an equation to help me determine it.
 


Originally posted by ML
I appreciate these replies but i was focusing more on the actual force that the buoy would be capable of pulling upwards or an equation to help me determine it.

The boyuant force is the difference between the mass of water displaced and the mass of the object.
 


Originally posted by ML
I appreciate these replies but i was focusing more on the actual force that the buoy would be capable of pulling up wards or an equation to help me determine it.

The buoyant force is the difference between the mass of water displaced and the mass of the object.

Your 1 m3 displaces 1000kg of water so experiences buoyant force equivalent to the weight of 1000kg of water B=mg= 9.8x103 N, the body has a weight of 9.8*20N. The difference is the weight required to keep the body submerged.
 
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