Physics 34 Fluid Dynamics (17 of 24) Poisseuille's Law and the Discharge Rate

[@cedricmmangisa385]

I've been studying this and i couldn't make sense of it. Thank you very much; You're a lifesaver 🙏

[@MichelvanBiezen]

You are welcome. Glad you found our videos.

[@fatilyuz4011]

thank you ı came here as a medical student. seing Poisseuille's Law as a mold wasnt't enough for me you made me understand blood flow in relevance with vessel diameter with just 2 videos :)

[@MichelvanBiezen]

Glad to be of help. Keep working hard in medical school, you are almost there.

[@tomatrix7525]

This is very very very very very very very good, forgive my repition but it was necessary. This is so understandable and relevant

[@andrewjustin256]

2:03 Mr. Michel, why is dA = 2#r dr and not simply dA = 2#dr? That's why I thought it would be!

[@oghenemoses8839]

Sir, thanks for all you do for us we really appreciate it. Sir , you didn't introduce a constant after the integration of dQ.(D discharge flow rate).

[@MichelvanBiezen]

There are no constants introduced when we have a definite integral. (An integral with limits to be evaluated).

[@jorenpetrus1449]

Hi Michel, This is very good material. Do you have a video where you calculate pressure drops in a pipe? Where you calculate Reynolds number, look up/calculate friction values of the inner surface of the pipe, ...?

[@MichelvanBiezen]

Not yet. Our videos on fluid dynamics are limited. We plan to expand those videos to include the topics you mentioned.

[@sneakyrabbits]

What happened to lecture 18 of 25? Your videos are great btw

[@MichelvanBiezen]

+sneakyrabbits I still have to finish the playlist.

[@jorgemercent2995]

Dear Prof van Biezen, @2:00, could you please explain why dA is 2Pie r dr? Shouldn't dA just be 2Pie dr?

[@MichelvanBiezen]

If you cut the circular ring (dA) and stretch it lengthwise you end up with a thin rectangular strip. The area of the rectangular strip = length x width = (2 x pi x r) x (dr)

[@jorgemercent2995]

@@MichelvanBiezen thank you Prof van Biezen very much for your reply, you are the best!

[@prof.dr.sadiqs.muhsunal_ji6353]

Dear sir Does this equation exceptable for Turbulent flow?

[@MichelvanBiezen]

When the flow becomes turbulent, this method no longer works.

[@rjbrewer57]

this is what for which I was delving!

[@MichelvanBiezen]

Great! Glad you found our videos. 🙂

[@noyesharrigan6217]

Great videos! I'm using these to prepare for my Hydraulics class. One question: If we're assuming p1 > p2, shouldn't the 'change in pressure' term be (p1 - p2), making it and the discharge rate positive?

[@MichelvanBiezen]

Noyes Harrigan I wouldn't get hung up on the sign. I always encourage understanding that the flow direction will be from high pressure to low pressure.

[@manideepikamallavarapu7372]

Thank you so much :') I wish I was your student! Physics would have been so much interesting.

[@johnbahati2405]

Well explained

[@MichelvanBiezen]

Thank you. 🙂

[@marwansallouta2101]

Thank you, very useful. I could not find Fluid Dynamic (18 of 25).

[@MichelvanBiezen]

You are correct. We couldn't find it either. It may have been skipped by accident. We'll see if we can figure it out.

[@marwansallouta2101]

Highly appreciated, thank you again.

[@aquienpuedaimportar3028]

If Q = Av, why does dQ = vdA and not dvdA?

[@MichelvanBiezen]

It could. It depends on what you are integrating or the variable over which you are integrating. In this case the velocity changes as a function of r and thus you are integrating over dr which can be defined via dA.

[@aquienpuedaimportar3028]

OK, thanks very much. Also, why does A = 2.pi.r and not 2.pi.r.L? Is the discharge rate independent of the length of the capillary?

[@chandramoulisarkar2935]

A quien pueda importar no the discharge rate does not depend upon the length it only depends upon the cross section the wider the cross section slower the discharge velocity and narrow the tube faster the discharge velocity. Length does not affect the velocity of discharge here as it is already considered under v: rate of flow of water . So Q=v.A

[@zouaidihajar1651]

please when can I find the following videos from 18 to 25 thanks

[@MichelvanBiezen]

They still need to be made. (A project for the future).

[@Trishaanne_]

teaches very well. thumbs up and God Bless

[@notSavant]

Is there any video where you explain why we can always calculate for a small amount like dA or dV... like in the moment of inertia of a big object?

[@MichelvanBiezen]

The concept of a dA of dV is simple geometry. It is no difference as the concept of dx which approaches zero in the limit. This is illustrated in the playlist: CALCULUS 1 CH 1 LIMITS & DERIVATIVES kzbin.info/aero/PLX2gX-ftPVXVzRDO_yw83HFddu5rfWsOX

[@notSavant]

ok, thanks :)

[@tesfayohanis2788]

Thanks teacher

[@MichelvanBiezen]

You are welcome

[@pppppppppianolover6618]

U r awesome sir

[@MichelvanBiezen]

Glad you are enjoying the videos.

[@yonasnegusse5294]

Great again.

[@MichelvanBiezen]

Keep it going. 🙂

[@gauravsaimaddipati8356]

Beautiful

[@MichelvanBiezen]

Thank you

[@learnallthings3695]

dQ=vdA why not A dv?

[@MichelvanBiezen]

In depends on what is changing. Since dV/dt = vA changes as a function of radius, and dA = 2 pi r dr, you want to express dQ as v dA

[@learnallthings3695]

@@MichelvanBiezen thank you you give us a great power best regards

[@Mantukasi]

Why you are using 2*pi*r*dr instead of 2*pi*r*dr+pi*(dr)^2? The later one is more correct... I think you neglect pi*(dr)^2 part as very small and that lets you solve integral. However I think that it should be mentioned.

[@MichelvanBiezen]

pi*dr^2 is not part of the integral

[@pok8070]

why you use 2(pi)rdr for dA ?

[@MichelvanBiezen]

dA is the area of a small ring that has the circumference 2*pi*r and the width dr, thus the area, dA = (2*pi*r) * dr

[@pok8070]

+Michel van Biezen thank you for answer . but i still understand that why dr is width . if dr is width that mean you calculate the space surroud the parabola of lamina flow ? why don't use width = R-dr ?

[@justinfoto]

why dr is width: imagine a circle being made of a lot of little rings. 2*pi*r*dr is the area of one little ring. when you integrate that from 0 to R, you'll get the area of the entire circle, pi*R^2

[@Theunreachable777]

thank you :)

[@MichelvanBiezen]

You're welcome!