Understanding Submarine Pressure: Importance and Calculations"

  • Context: Undergrad 
  • Thread starter Thread starter Misr
  • Start date Start date
  • Tags Tags
    Pressure Submarine
Click For Summary

Discussion Overview

The discussion revolves around the calculations of pressure in submarines, particularly the relationship between external water pressure and internal atmospheric pressure. Participants explore the implications of these pressures on submarine design and operation, addressing both theoretical and practical aspects.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant presents a formula for pressure in a submarine, questioning why atmospheric pressure is neglected in certain calculations.
  • Another participant argues that the pressure inside a rigid hull submarine can be determined by the designer and is independent of external pressures.
  • A participant reiterates the formula for pressure, emphasizing the difference between external and internal pressures and questioning the relevance of atmospheric pressure in calculations.
  • Concerns are raised about the clarity of the formula and the significance of neglecting atmospheric pressure when calculating external pressure.
  • Another participant clarifies that the pressure differential on the hull can be calculated by subtracting the internal pressure from the external pressure, leading to a simplified expression.

Areas of Agreement / Disagreement

Participants express differing views on the relevance of atmospheric pressure in submarine pressure calculations. Some argue for its inclusion, while others maintain that it can be neglected, leading to an unresolved discussion on the topic.

Contextual Notes

There are unresolved assumptions regarding the definitions of pressure in this context, as well as the conditions under which the equations apply. The discussion does not clarify the specific scenarios or depths being considered.

Who May Find This Useful

This discussion may be of interest to those studying submarine design, fluid mechanics, or pressure calculations in engineering contexts.

Misr
Messages
384
Reaction score
0
The pressure in a submarine inside water
P=h*ρ*g+Pa
Okay,
Since there's Atmospheric pressure inside the submarine (Pa),we calculate the total pressure on the submarine from the relation=h*density*g
we just neglect the atmospheric pressure
why?I don't understand?
Why don't we calculate the total pressure from the relation P=hρg+2Pa?
does the atmospheric pressure in the submarine have a different direction?
 
Physics news on Phys.org
Where did you get those equations? For a rigid hull sub, the pressure inside can be whatever the designer and operator choose. You can't calculate it.
 
Misr said:
The pressure in a submarine inside water
P=h*ρ*g+Pa
Okay,
Since there's Atmospheric pressure inside the submarine (Pa),we calculate the total pressure on the submarine from the relation=h*density*g
we just neglect the atmospheric pressure
why?I don't understand?
Why don't we calculate the total pressure from the relation P=hρg+2Pa?
does the atmospheric pressure in the submarine have a different direction?

Why not ?
Do you know how less in the atmospheric pressure as in comparison to water exerting pressure on submarine below water ? Moreover atmospheric pressure is exerted maximum on surface of water. Do you know how below is the submarine from surface level ?

Counter question having same logic : Why do you think air friction is neglected during free fall of body ?

Pressure inside is independent of outside , yes Halls.
These are opposite too. You just can't add them Misr.
:)

@ HallsofIvy and Russ Watters
[I thought he was only referring to atmospheric pressure on surface of water.]
 
Last edited:
Even "general physics" questions have to make sense. A submarine is made of rigid metal. The pressure on the outside (as long as it is not great enough to fracture the metal) is completely independent of the pressure on the inside.
 
The formula (which would be clearer if all symbols were defined) appears to be that on the outside of the submarine. Since almost all the outside pressure is from the water, neglecting the air pressure doesn't make much difference. Also the air pressure on the inside may be kept (for comfort) at roughly that of the surface air pressure, so the pressure formula would give the net pressure on the hull.
 
Pressure outside the submarine hull = h*ρ*g+Pa
Pressure inside the submarine hull = Pa

Pressure differential on the hull = outside pressure - inside pressure = h*ρ*g + Pa - Pa = h*ρ*g
 
Resolved
Thanks very much
 

Similar threads

  • · Replies 12 ·
Replies
12
Views
2K
  • · Replies 14 ·
Replies
14
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 24 ·
Replies
24
Views
5K
  • · Replies 20 ·
Replies
20
Views
4K
Replies
1
Views
2K
  • · Replies 6 ·
Replies
6
Views
1K
Replies
11
Views
3K