Pressure changes of a fluid flowing through a horizontal pipe

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Discussion Overview

The discussion revolves around the concept of pressure changes in a fluid flowing through a horizontal pipe, exploring whether a pressure difference is necessary for fluid flow. It also draws parallels with electrical current and Ohm's law, examining the implications of voltage and resistance in both fluid dynamics and electrical circuits.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions whether a pressure difference is necessary for fluid flow, suggesting that pressure measurements at two points in a horizontal pipe could be the same.
  • Another participant references Newton's first law to argue that an object in motion will continue at constant velocity unless acted upon by an external force, implying that pressure difference may not be required under certain conditions.
  • A different viewpoint states that if friction and viscosity are significant, a pressure gradient is necessary to drive the flow; otherwise, the pressure at two points will be equal.
  • One participant proposes an analogy using electrons and Ohm's law, questioning if a zero voltage implies zero current and whether this constitutes a violation of Ohm's law.
  • Another participant responds that it is not a violation, providing a mathematical example to illustrate that zero voltage can correspond to zero current without needing to neglect resistance.
  • Further discussion raises the issue of interpreting a zero current with zero voltage and resistance, with one participant suggesting that inertia might play a role in current flow.
  • Another participant cautions against trying to derive physical meaning from the mathematical result of 0/0, emphasizing adherence to physical laws and the importance of recognizing the limitations of simplifications.

Areas of Agreement / Disagreement

The discussion features multiple competing views regarding the necessity of pressure differences for fluid flow and the interpretation of electrical current in relation to voltage and resistance. No consensus is reached on these points.

Contextual Notes

Participants express uncertainty regarding the implications of zero values in both fluid dynamics and electrical circuits, highlighting the complexity of these concepts and the potential for nonsensical results from oversimplifications.

Photo1234
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If we have a tube of fluid going like it is shown in the picture, and we measure pressure at two points we would get the same value. But the fluid is still going from point A to point B. So is pressure difference not necessary for fluid flow or I made some other wrong assumptions?
 

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Photo1234 said:
So is pressure difference not necessary for fluid flow
Newton's first law. An object in motion will continue in motion at a constant velocity unless acted on by an outside force.
 
If friction and viscosity is significant you will need a pressure gradient to drive the flow. If they are not, the pressure in the two points will be the same.
 
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What if we use electrons instead of fluid and use Ohms law V = R * I for two points like that, and If V = 0, that current should also be 0. Is that violation of Omhs law?
(We neglect resistance of the wire)
 
Photo1234 said:
What if we use electrons instead of fluid and use Ohms law V = R * I for two points like that, and If V = 0, that current should also be 0. Is that violation of Omhs law?
(We neglect resistance of the wire)

No it is not a violation and it does not need us to neglect the resistance. Let us say R=1, Then V=R*I means 0=1*0. Same answer if R=1000.
 
If we look at two points with the sam voltage in the circuit, then V=0, and R=0, but current flows.
 

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Did you understand the answer in post #3?
 
So I = V/R = 0/0

And what causes current if not voltage? Inertia?
 
Photo1234 said:
So I = V/R = 0/0

And what causes current if not voltage? Inertia?
You're trying to find a physical meaning for an assumed - not real - mathematical result of 0/0. There really isn't one. Stick to the physical laws. Stick to the answer you got in post #3 and recognize that simplifications are sometimes useful, but sometimes give nonsensical results.
 
  • #10
russ_watters said:
You're trying to find a physical meaning for an assumed - not real - mathematical result of 0/0. There really isn't one. Stick to the physical laws. Stick to the answer you got in post #3 and recognize that simplifications are sometimes useful, but sometimes give nonsensical results.

What abaut this:
Photo1234 said:
And what causes current if not voltage? Inertia?
 
  • #11
Sorry, this question has been answered several times.

@Photo1234 go back and re-read the answers.

Thread closed.
 

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