Pressure in Fluids: What's Really Going On?

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    Fluid Pressure
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Discussion Overview

The discussion revolves around understanding pressure in fluids, particularly in a system with two pipes containing fluid at different heights. Participants explore concepts related to fluid pressure, the role of atmospheric pressure, and the behavior of fluids at rest versus their particle motion.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether the pressure at the top of the water in pipe 1 equals the pressure at the same level in pipe 2, expressing confusion about the nature of pressure in fluids.
  • Another participant suggests that the pressure in the system may be due to pressurized air rather than the water itself, arguing that the water does not compress under normal circumstances.
  • A later reply clarifies that the pressure on the surface of the water in pipe 1 must equal the upward pressure from the water below, introducing the concept of pressure difference as ρgh, where h is the height difference between the two pipes.
  • One participant seeks further understanding of the pressure relationship by asking for a demonstration in terms of forces, indicating a desire for a more concrete explanation.

Areas of Agreement / Disagreement

Participants express varying interpretations of fluid pressure and its components, with no consensus reached on the nature of pressure in the system or the implications of particle motion within the fluid.

Contextual Notes

There are unresolved assumptions regarding the definitions of pressure in fluids, the role of atmospheric pressure, and the conditions under which fluids are considered at rest. The discussion also reflects differing views on the compressibility of water and the effects of air pressure.

Who May Find This Useful

This discussion may be of interest to individuals studying fluid mechanics, physics students grappling with concepts of pressure, or anyone curious about the behavior of fluids in different conditions.

aaaa202
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Suppose I have a fluid in a system like the one on the picture. The fluid is lower in one of the pipes because the pressure in this pipe is bigger than the atmospheric pressure.
But is it then so that the pressure in the top of the water of pipe 1 equals the pressure of the water in the same level in pipe 2?
I really have a hard time understanding pressure in fluids. I mean how can you talk about for instance the pressure being bigger in the bottom of a fluid because it is a rest - indeed the fluid is not at rest since the particles in it are continuously moving around..
 
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I'm not sure what picture you are talking about, but if I am not mistaken the water would not actually compress(I don't think you can have compressed water under normal circumstances, but I am probably wrong), but rather the air in the pipe is pressurized. When the air is pressurized it will try to expand, so to speak. Since the air and water can not occupy the same space, the air will push the water out of the way. So, in summary, if I am not mistaken the water itself does not have a pressure, but rather the pressurized air exerts a force on the water. As for your last question, I believe when we say the water is at rest we are not referring to anything as small as particles, but as a whole. By that logic no object is ever at rest. I think when we say water in a cup is at rest, it simply means the water is not moving around in the cup(but the particles the water consist of are). I hope that helps.
Edit: didn't read the op too well, for some reason I thought you were talking about water, so what I said probably doesn't apply here.
 
okay thanks. I forgot to attach the picture so here it is. Does that make you change explanation? Indeed the pressure on the surface of the water in pipe 1 must be as big as the upwards pressure from the water below. But is this pressure then equal to ρgh, where h is the difference in height between the water in the two pipes?
 

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The pressure on the surface of the liquid in tube 1 is equal to
[tex]\rho g h + P_{atm}[/tex]
[tex]\rho g h[/tex] is the pressure difference.
 
nasu said:
The pressure on the surface of the liquid in tube 1 is equal to
[tex]\rho g h + P_{atm}[/tex]
[tex]\rho g h[/tex] is the pressure difference.

Hmm how can I realize that is true? Can you show me in terms of forces..? :)
 

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