Understanding Pressure Imbalance in a U-Tube: Exploring Fluid Mechanics

In summary, the conversation discusses a u-tube filled with liquid and the concept of force and pressure acting on it. It is noted that while the force of the atmosphere is greater on one side, the sides of the tube also exert an upward force, resulting in a net force of zero on the liquid. The conversation also mentions a helpful discussion and an analogy to explain the concept better. Finally, a question is raised about the acceleration of an object with different masses and forces acting on it.
  • #1
tsochiu
17
0
There is a u-tube which its diameter on the left hand side is smaller than the right hand side.
It is filled with liquid.
As the atmosphere pressure is equal in the two side, and force = pressure*area.
I want to ask, why the liquid in the u-tube is not pushed to the left side as the force from atmosphere on the right side is larger than left? Or what is wrong in my concept?
 
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  • #2
While it's true that the force of the atmosphere is greater on the right side surface, that's not the only force acting on the liquid: The sides of the tube also exert an upward force on the right hand side. (The details depend on the exact shape of the tube.) The net force on the liquid will be zero.
 
  • #3
Sorry, I cannot understand it clearly, could you give me an example on how the force is balanced? With a free body diagram will be better. Thank you very much
 
  • #4
Why don't you provide a diagram of the U-tube in question.

You might find this discussion helpful: http://scubageek.com/articles/wwwparad.html" [Broken]
 
Last edited by a moderator:
  • #5
Your web page is really helpful. I can understand what is happening in the u-tube now.
That is when the u-tube start to narrow,the wall of the u-tube will give a reaction force toward the liquid which will cancel out the extra force due to the wider mouth.
Thanks for your help, it solve my great problem with pressure.
 
  • #6
If you push on an object with twice the force with which you push on an object of half the mass, which will accelerate faster?
 
  • #7
tsochiu said:
That is when the u-tube start to narrow,the wall of the u-tube will give a reaction force toward the liquid which will cancel out the extra force due to the wider mouth.
Exactly.

russ_watters said:
If you push on an object with twice the force with which you push on an object of half the mass, which will accelerate faster?
Regardless of the mass of the fluid, if there's a net force on it, it will accelerate. The problem here is in thinking that the only force on the fluid is that due to atmospheric pressure.
 
  • #8
It was an analagous situation, not an analysis of this situation.
 
  • #9
I guess I didn't see the analogy.
 

1. What is fluid mechanics?

Fluid mechanics is the branch of physics that deals with the study of fluids, which includes liquids and gases, and their behavior when they are in motion or at rest.

2. How is pressure defined in fluid mechanics?

Pressure in fluid mechanics is defined as the force per unit area exerted by a fluid on its surroundings. It is usually measured in units of Pascals (Pa) or Newtons per square meter (N/m2).

3. What is the difference between absolute and gauge pressure?

Absolute pressure is the total pressure exerted by a fluid, including atmospheric pressure. Gauge pressure, on the other hand, is the difference between the absolute pressure and the atmospheric pressure. It is often used to measure the pressure difference in a system.

4. How does Bernoulli's principle relate to fluid mechanics?

Bernoulli's principle states that in a fluid flow, an increase in the speed of the fluid will result in a decrease in pressure. This principle is commonly used to explain the lift force on airplane wings and the flow of fluids through pipes.

5. What are some real-life applications of fluid mechanics and pressure?

Fluid mechanics and pressure have many practical applications in our daily lives, such as in plumbing systems, hydraulic machines, and in the design of airplanes and cars. They are also important in the study of weather patterns and ocean currents.

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