Understanding pressure in fluids

In summary, the conversation is about the understanding of pressure in fluids. The speaker is confused about how pressure is applied to fluids and why it increases when going deeper into the fluid. They also question how a stationary fluid can be described as "at rest" when the particles that make it up are constantly moving. The other person explains that pressure is the force exerted by the particles on an area, and it increases with depth due to gravity. They also mention that in a stationary fluid, the forces must be in equilibrium, and in a flowing fluid, the particles move and change shape but still stay within the same area.
  • #1
aaaa202
1,169
2
Okay so I already asked a bit about this, but I think I'm going to need to post several questions on this to understand it, so here goes:

I understand the definition of pressure, just not how it is applied to fluids. How is pressure in a fluid to be interpreted. Is it the force that the particles that make up the fluid exert on an area in the fluid? I think that is correctly understand, but then I just don't understand why the pressure gets bigger the farther you are down a fluid. Why would the total force that the nearby particles exert on your area (we could imagine a thin disk in the fluid) depend on how many particles that are above you?
And further I don't even get how you can say things like this (which my book often does): Every little cube inside the fluid is at rest etc etc. Indeed the fluid is never at rest since, the particles that make it up are whirling around! What am I getting wrong?
 
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  • #2
hi aaaa202! :smile:

And further I don't even get how you can say things like this (which my book often does): Every little cube inside the fluid is at rest etc etc. Indeed the fluid is never at rest since, the particles that make it up are whirling around! What am I getting wrong?

no, in a stationary liquid, the particles ain't goin' nowhere …

they bump up against other particles, and transfer energy to them, but that's it …

the cube stays as it is :smile:​

(in a flowing liquid, the cube moves and changes shape slightly, but the particles that make it up stay inside it)

(in a gas, I'm not so sure :redface:)
aaaa202 said:
How is pressure in a fluid to be interpreted. Is it the force that the particles that make up the fluid exert on an area in the fluid?

yes
… I just don't understand why the pressure gets bigger the farther you are down a fluid. Why would the total force that the nearby particles exert on your area (we could imagine a thin disk in the fluid) depend on how many particles that are above you?

it only gets bigger if there's gravity …

look at a a thick disc …

it's in equilibrium, so the force upward (from below) must equal the force downward (from above) plus the weight of the disc! …

ie pressure below = pressure above + ρgh :wink:
 

What is pressure in fluids?

Pressure in fluids is the force per unit area exerted by a fluid, such as a liquid or gas, on the walls of its container or any object submerged in it. It is measured in units such as pascals (Pa) or pounds per square inch (psi).

What causes pressure in fluids?

Pressure in fluids is caused by the collisions of molecules within the fluid, which create a force that is distributed evenly throughout the fluid. The weight of the fluid itself also contributes to the overall pressure.

How does pressure change in fluids?

Pressure in fluids can change depending on various factors, such as the depth of the fluid, the density of the fluid, and the force of gravity. For example, in a column of fluid, the pressure increases with depth due to the weight of the fluid above it.

How is pressure transmitted in fluids?

Pressure in fluids is transmitted uniformly in all directions. This means that when a force is applied to one part of a fluid, the pressure will be distributed equally throughout the entire fluid, including to the walls of its container.

What are some real-world applications of understanding pressure in fluids?

Understanding pressure in fluids is essential in many fields, such as engineering, meteorology, and medicine. It is used to design structures like dams and bridges, predict weather patterns, and measure blood pressure in the human body.

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