What is the relationship between depth and pressure in water?

  • Context: High School 
  • Thread starter Thread starter DaveC426913
  • Start date Start date
  • Tags Tags
    Logarithmic Water
Click For Summary

Discussion Overview

The discussion revolves around the relationship between depth and pressure in water, particularly in the context of diving and the physiological effects of pressure changes on the human body. Participants explore concepts related to pressure, lung overpressure, and nitrogen absorption, with a focus on how these factors influence safety during diving activities.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants assert that pressure increases linearly with depth due to water's incompressibility, suggesting that 1.25 atm would be reached at a depth of 8.25 ft.
  • Others argue that pressure differences are not linear, noting that the percentage change in pressure is greater closer to the surface, which could imply that 1.25 atm is reached at a shallower depth than 8.25 ft.
  • There are claims regarding the limits of human lungs under pressure, with some stating that lungs can withstand a 25% overpressure before damage occurs.
  • Participants discuss anecdotal evidence of lung injuries occurring at shallow depths, with varying accounts of circumstances leading to such injuries.
  • Some participants highlight the importance of understanding the physiological effects of pressure changes, including the risks of nitrogen absorption and overpressure in the lungs.
  • Technical discussions include the effects of breathing air at different pressures and how this affects lung volume during ascent and descent.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the relationship between depth and pressure, particularly concerning the linearity of pressure changes and the implications for lung safety. The discussion remains unresolved, with no consensus reached on the exact depth at which 1.25 atm is encountered.

Contextual Notes

Participants note the complexity of the topic, including the need to consider various factors such as individual physiology, diving conditions, and the specific circumstances of lung injuries. There is also mention of the limitations of anecdotal evidence in understanding the risks associated with diving.

  • #31
Studiot said:
Oh for goodness sake read post14.

Your formula gives a pressure of zero for h=0, not good news for any breathing animal.

Which is true, since the hydrostatic pressure is zero at the water surface. Also, this has nothing to do with the coefficient \Delta P/\Delta h since an addition of a constant cancels out when calculating the slope.
 
Physics news on Phys.org
  • #32
Which is true, since the hydrostatic pressure is zero at the water surface.

This is just plain old fashioned wrong.

The hydrostatic pressure at the water surface equals the atmospheric pressure there. The pressure difference (as mentioned by Russ) is zero.

Of course the slope (which you calculated) is the same - this is true of any linear relationship.
 
  • #33
Studiot said:
This is just plain old fashioned wrong.

The hydrostatic pressure at the water surface equals the atmospheric pressure there.

You seem so confident. How would you go on proving this?
 
  • #34
If it wasn't the atmosphere would be pushing the water aside.
 
  • #35
Studiot said:
If it wasn't the atmosphere would be pushing the water aside.

So, according to you, the water acts on itself to be in equilibrium with an external force applied to it. Nice. What's next. Perpetually moving machines?
 
  • #36
I've tried to be subtle here and I've tried to be nice.

The free surface of any liquid on this planet is subject to the local atmospheric pressure on the gas side of the boundary. This is balanced exactly by liquid hydrostatic pressure on the liquid side of the boundary. At sea level this pressure is defined as 1 atmosphere.
 
  • #37
Studiot said:
I've tried to be subtle here and I've tried to be nice.

The free surface of any liquid on this planet is subject to the local atmospheric pressure on the gas side of the boundary. This is balanced exactly by liquid hydrostatic pressure on the liquid side of the boundary. At sea level this pressure is defined as 1 atmosphere.

No, this is not true. Pressure gets transmitted through bulk materials in all directions. The pressure at the sea level is solely due to the column of air above it, hence it is atmospheric and has no hydrostatic contribution.
 
  • #38
So are you are saying that the air pushes on the liquid, but the liquid does not push back equally on the air?
 
  • #39
Studiot said:
So are you are saying that the air pushes on the liquid, but the liquid does not push back equally on the air?

So, let me ask you this. According to you, the pressure at any height is caused not only by the column of air + water above you pushing down due to its own weight, but also because the column of air + water below you pushes upwards. Pray tell, how does the pressure exerted on the object depend on the depth of the column of air + water below you?
 

Similar threads

Undergrad Relationship between Flow Rate and Distance of Water Droplet Travel in Air
  • · Replies 1 ·
Replies
1
Views
3K
Undergrad Simple Barometers & Air Pressure
  • · Replies 1 ·
Replies
1
Views
3K
Undergrad What Are the Complexities of Buoyancy and Common Misconceptions?
  • · Replies 48 ·
2
Replies
48
Views
12K
Undergrad Is the relationship between water pressure and gravity a direct correlation?
  • · Replies 4 ·
Replies
4
Views
19K
Graduate What is the relationship between hull shape and form drag on sailboats?
  • · Replies 3 ·
Replies
3
Views
2K
Vapor pressure of boiling water
  • · Replies 1 ·
Replies
1
Views
5K
Plumbing Compressed air powered water pressure
  • · Replies 39 ·
2
Replies
39
Views
16K
Writing: Input Wanted What are the Consequences of a Longer PETM?
  • · Replies 10 ·
Replies
10
Views
2K
How High Did Water Rise in the Squalus Diving Bell?
  • · Replies 6 ·
Replies
6
Views
4K
Graduate Not so simple buoyant forces in bubbling water
  • · Replies 11 ·
Replies
11
Views
11K