Pressure in Fluids: What's Really Going On?

In summary, the conversation discusses the pressure in a fluid system and how it is affected by differences in height and the presence of air. It is concluded that the pressure on the surface of the liquid in tube 1 is a combination of the pressure difference due to height and the atmospheric pressure. The conversation also touches on the concept of rest in fluids and how it is relative to the movement of particles. The question about forces is left unanswered.
  • #1
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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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  • #2
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.
 
  • #3
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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  • #4
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.
 
  • #5
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..? :)
 

FAQ: Pressure in Fluids: What's Really Going On?

What is pressure in fluids?

Pressure in fluids refers to the force exerted by a fluid on its surroundings. It is the result of the molecules of the fluid colliding with each other and with the walls of the container. In other words, it is the measure of how much the fluid is pushing against its boundaries.

How is pressure in fluids measured?

Pressure in fluids is typically measured in units of force per unit area, such as pounds per square inch (psi) or pascals (Pa). This can be done using instruments such as a pressure gauge or a manometer, which can measure the force exerted by the fluid on a given area.

What factors affect pressure in fluids?

Pressure in fluids is affected by several factors, including the density of the fluid, the depth of the fluid, and the acceleration due to gravity. For example, the deeper the fluid is, the higher the pressure will be due to the weight of the fluid above it. Additionally, compressibility and temperature can also affect the pressure in fluids.

What is the relationship between pressure and depth in fluids?

In a fluid at rest, the pressure increases with depth. This is because the weight of the fluid above exerts a force on the fluid below, causing an increase in pressure. This relationship is known as Pascal's law, which states that pressure in a fluid is transmitted equally in all directions.

How does pressure in fluids affect objects immersed in them?

Objects immersed in fluids experience a force known as buoyancy, which is the upward force exerted by the fluid on the object. This force is equal to the weight of the fluid displaced by the object. The amount of buoyancy depends on the density of the fluid and the volume of the object. If the object is less dense than the fluid, it will float, while if it is more dense, it will sink.

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