Air pressure stays the same or increase?

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Discussion Overview

The discussion revolves around the behavior of air pressure in a sealed barrel as water is added from a hose. Participants explore whether the air pressure in the barrel remains constant or increases as the water level rises, considering theoretical and practical implications.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant asserts that the air pressure will increase significantly above atmospheric pressure as water fills the barrel, but notes that this is theoretical due to practical limitations of tap water pressure.
  • Another participant suggests that the water level will rise until the air pressure equals the tap water pressure, implying a limit to how high the water can go.
  • There is speculation about whether air molecules might dissolve in water as the water level rises, which could affect air pressure, although this is challenged by a later comment stating that air is not very soluble in water.
  • One participant confirms that as the air volume decreases, the pressure must increase, reinforcing the idea that the air is being compressed.
  • A participant proposes the idea of using an air pressure gauge to measure the pressure in the barrel as water is added, suggesting a practical approach to the theoretical discussion.

Areas of Agreement / Disagreement

Participants generally agree that the air pressure will increase as water fills the barrel, but there are differing views on the extent of this increase and the implications of air solubility in water. The discussion remains unresolved regarding the practical limits of water pressure and the behavior of air in this context.

Contextual Notes

There are unresolved assumptions about the pressure of the tap water and the specific conditions under which the air pressure changes occur. The discussion also touches on the solubility of air in water, which is noted to be minimal.

Althepump
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the barrel has a lid at the top...sealed. I make a hole at the bottom to attach water hose to it. Then I turn on the water hose. The water volume in the barrel increases, no doubt about that. When It takes 7/8 of the barrel. Will the air in the top 1/8 of the barrel be compressed? I ask because the air has no way out. It has to be somewhere in the barrel.

Needless to say that the barrel is empty but air to begin with.
 
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Yes, of course it will. And its pressure will be much above the atmospheric. But that's in theory, because tap water is rarely available at pressures that high...
 
NTW said:
Yes, of course it will. And its pressure will be much above the atmospheric. But that's in theory, because tap water is rarely available at pressures that high...

I think I understand. Since you say tap water is rarely available at high pressure, therefore water level in the barrel will go as far as the air pressure in the top of the barrel is equal to the tap water pressure. Then it stops. Maybe the barrel can only go as far as half.
 
Hi
welcome to PF :)

what do you think would happen ?

if you think it would stay the same ... give a reason for that thought
likewise, if you think it would increase ... give a reason
and we will see how you do

cheers
Dave
 
davenn said:
Hi
welcome to PF :)

what do you think would happen ?

if you think it would stay the same ... give a reason for that thought
likewise, if you think it would increase ... give a reason
and we will see how you do

cheers
Dave

I was not sure... I thought air molecules may seep into water as water level increases like air bubbles in water. In other words, dissolve in water. If it does happen, then air pressure will be about the same. But I got reply earlier that pressure does increase in theory. It confirms my hunch.
 
Last edited:
Althepump said:
I was not sure... I thought air molecules may seep into water as water level increases like air bubbles in water. In other words, dissolve in water. If it does happen, then air pressure will be about the same. But I got reply earlier that pressure does increase in theory. It confirms my hunch.
Air is not very soluble in water. Only a tiny fraction would dissolve.

Chet
 
Chestermiller said:
Air is not very soluble in water. Only a tiny fraction would dissolve.

Chet

Thanks for the confirmation. I thought so.
 
there you go :)

when you just think about it simply ... you are squeezing the air into a smaller and smaller volume inside the
container. It can do nothing but increase in pressure

cheers
Dave
 
Ok. By now I may go a step further by putting an air pressure gauge into the top barrel to get readings. I believe I can simply plug it in provided sealed.
 

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