# Pressure changes of a fluid flowing through a horizontal pipe

• I

## Main Question or Discussion Point

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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jbriggs444
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2019 Award
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.

Orodruin
Staff Emeritus
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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.

• russ_watters and Chestermiller
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)

anorlunda
Staff Emeritus
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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anorlunda
Staff Emeritus
Did you understand the answer in post #3?

So I = V/R = 0/0

And what causes current if not voltage? Inertia?

russ_watters
Mentor
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.

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:
And what causes current if not voltage? Inertia?

anorlunda
Staff Emeritus
Sorry, this question has been answered several times.