Physics 34 Fluid Dynamics (16 of 24) Derivation of Poisseuille's Law

In this video I will derive Poisseuille's Law, v= f(r)=?

Next video in this series can be seen at:

[hmata]

Thanks for uploading these types of videos! Fluids may have been much easier if I had this channel years ago! :D

[markmccoy]

if only you could be my lecturer! thanks !!!

[CADPond]

WOW! I have been staring at my lecture notes for a while now. And your explanation just made it easy to understand. Thank you sir!

[Wook]

A Fluid Mechanics problem that I'm trying to work out. A viscometer of the Redwood type has an oil-containing cylinder 4.75cm in diam and an agate tube 0.17 cm in diameter and 1.2 cm long. The oil surface, when flow starts, is 9 cm above the outlet from the agate tube. To allow for the sudden contractions at entry to the tube, the effective length of the tube may be taken as the actual length plus the tube radius. Making allowance for the decreasing head of oil, the viscous resistance through the tube, and the KE (kinetic energy) of discharge, calculate using arithmetical integration, the time required for 50 cm3 of an oil of viscosity 0.5 poise and specific gravity 0.92 to flow through the viscometer. How do you find the time? From this question, I have tried to use quadratic equation to solve for v, but it is proving more difficult than I thought

[siddharthannandhakumar]

For finding Fd, shouldn't you have used 'R' instead of 'r' ? How could you cancel the radius on both sides of equation before integrating it? Or is it possible to cancel variables like this in maths?

[mosaovirkhan]

Anyone else think he kinda sounds like Gru from despicable me

[batbaatarboldbaatar]

wow that's easy to understand to me. thank you keep it !

[nourharb]

Excuse me but I don't understand why the frictional force is calculated like that I know the formula but I fail do understand why we only use that force at that radius when the rest of the section that we selected to study also experiences friction at each radius...can you please clarify this thank you!

[gaurangagarwal]

Thank you Michael I am so grateful to you.

Secondly we can derive for volume flow rate from here

For a cylinder of thickness dr the volume flow rate is v(r)×2πrdr integrate this from 0 to R we get
V/t = (∆pπR^4)/8nl

[geraudamoussou]

I can't thank this guy enough. He always help me understand the fluids dynamics concepts I'm struggling with. Thanks a lot.

[mj..]

Hello, I'm a high school student in Korea. Thank you for your useful video. However, I can't understand the reason for the differential coefficient in FsubR's formula. I'll appreciate it if you explain it to me.

[antonofka]

There's a subtle detail that is not clear at first. At least for me. It cost me 2 hours of thorough mental processing :)

[hayin]

Thank you for the clear presentation. But I read Calculus: early transcendentals, and it said that this equation is called the law of laminar flow.

[ashwinaravindaraj]

why there it is πx^2 in driving force and in resisting force it is 2πxl

[rjbrewer]

I thought there was an r to the 4th power in pouiselles law?

[philwesom]

why does the dv/dr term appear in the force equation?....any theoretical explanation pls...

[manideepikamallavarapu]

But how is
Velocity (avg.) = (∆P)R^2/8πL

[thecurios]

Thank you sir 😊.Your way of teaching and your language both are fabulous.

[mohamedossama]

why area is nt equal to 2*pi*r*dr while deriving the velocity

[SuperDanisse]

Is it correct to say that the negative sign comes from the direction in which the viscous forces act? For me it's easier to understand that friction forces are opposed to the movement. Great explanation!