Can Different Curvatures Exist in Equilibrium for Fluid-Filled Pipe?

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Discussion Overview

The discussion centers on the possibility of different curvatures existing in equilibrium for fluid-filled pipes, specifically considering the implications of pressure gradients and external forces. Participants explore theoretical scenarios involving gravitational effects and atmospheric pressure.

Discussion Character

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

Main Points Raised

  • One participant suggests that different curvatures cannot exist in equilibrium due to the relationship between pressure and curvature as described by the Young-Laplace equation.
  • Another participant counters that a pressure gradient can exist in equilibrium if balanced by another force, citing examples such as water pressure in a pool and atmospheric pressure variations.
  • A later reply questions whether constant curvatures would be necessary for equilibrium in the absence of gravity and with constant atmospheric pressure.
  • Another participant posits that without external forces, a zero pressure gradient would imply equal curvatures at both ends of the pipe.
  • One participant emphasizes the definition of equilibrium, stating that for a pressure gradient to exist, the system cannot be in equilibrium unless counteracting forces are present.

Areas of Agreement / Disagreement

Participants express differing views on the conditions under which different curvatures can exist in equilibrium, indicating that the discussion remains unresolved with multiple competing perspectives on the role of pressure gradients and external forces.

Contextual Notes

Participants discuss the implications of gravity and atmospheric pressure on the equilibrium state, highlighting assumptions about external forces and pressure gradients that remain unresolved.

member 428835
Suppose we have a pipe of some length ##2L## and at the ends there is to spherical caps of fluid, as shown in the attachment. Is it possible for the two ends to have different curvatures in equilibrium?

My initial thoughts are no, since pressure is proportionate to curvature (Young-Laplace) and I don't think a pressure gradient would exist in equilibrium. What do you think?
 

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  • Screen Shot 2017-03-21 at 1.57.34 AM.png
    Screen Shot 2017-03-21 at 1.57.34 AM.png
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You can have a pressure gradient in equilibrium. You just need some other force acting to balance out the force from pressure. For example, water at the bottom of a pool is at much higher pressure than water at the top of a pool. Air pressure is much higher on the surface of the Earth than 2 miles above the surface. If your pipe is held vertically, than you would by necessity have a pressure gradient which would be equal to the density times Earth gravity times the depth.

Furthermore, you could have different atmospheric pressures applied to the different ends, though that might be reading way too much into it.
 
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Hmmm yea that makes a lot of sense. So in the absence of gravity and assuming atmospheric pressure to be constant, for equilibrium to exist the curvatures would have to be constant at both ends?
 
Assuming no other forces on the fluid in the pipe, than we'd have to assume zero pressure gradient and thus equal curvatures.
 
Thanks!
 
This just comes down to a definition of equilibrium. We're assuming all forces in the fluid are canceling each other out, so that the net force is zero. Pressure gradients indicate a force, so for a pressure gradient to exist the fluid either has to have some other force at work, or it has to not be in equilibrium.
 

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