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Section summary

  • Laminar flow is characterized by smooth flow of the fluid in layers that do not mix.
  • Turbulence is characterized by eddies and swirls that mix layers of fluid together.
  • Fluid viscosity η size 12{η} {} is due to friction within a fluid. Representative values are given in [link] . Viscosity has units of ( N/m 2 ) s size 12{ \( "N/m" rSup { size 8{2} } \) s} {} or Pa s size 12{"Pa" cdot s} {} .
  • Flow is proportional to pressure difference and inversely proportional to resistance:
    Q = P 2 P 1 R . size 12{Q= { {P rSub { size 8{2} } - P rSub { size 8{1} } } over {R} } } {}
  • For laminar flow in a tube, Poiseuille’s law for resistance states that
    R = 8 η l πr 4 . size 12{R= { {8ηl} over {πr rSup { size 8{4} } } } } {}
  • Poiseuille’s law for flow in a tube is
    Q = ( P 2 P 1 ) π r 4 8 η l . size 12{Q= { { \( P rSub { size 8{2} } - P rSub { size 8{1} } \) π`r rSup { size 8{4} } } over {8ηl} } } {}
  • The pressure drop caused by flow and resistance is given by
    P 2 P 1 = R Q . size 12{P rSub { size 8{2} } - P rSub { size 8{1} } =R`Q} {}

Conceptual questions

Explain why the viscosity of a liquid decreases with temperature—that is, how might increased temperature reduce the effects of cohesive forces in a liquid? Also explain why the viscosity of a gas increases with temperature—that is, how does increased gas temperature create more collisions between atoms and molecules?

When paddling a canoe upstream, it is wisest to travel as near to the shore as possible. When canoeing downstream, it may be best to stay near the middle. Explain why.

Why does flow decrease in your shower when someone flushes the toilet?

Plumbing usually includes air-filled tubes near water faucets, as shown in [link] . Explain why they are needed and how they work.

The picture shows water gushing out of a water tap. The faucet in the tap is marked. A pipe connected vertically filled with air is shown at an opening on the water pipe before the tap.
The vertical tube near the water tap remains full of air and serves a useful purpose.


(a) Calculate the retarding force due to the viscosity of the air layer between a cart and a level air track given the following information—air temperature is 20º C size 12{"20" rSup { size 8{ circ } } C} {} , the cart is moving at 0.400 m/s, its surface area is 2 . 50 × 10 −2 m 2 size 12{2 "." "50" times "10" rSup { size 8{2} } `m rSup { size 8{2} } } {} , and the thickness of the air layer is 6.00 × 10 5 m size 12{6 "." "00" times "10" rSup { size 8{ - 5} } `m} {} . (b) What is the ratio of this force to the weight of the 0.300-kg cart?

(a) 3 . 02 × 10 3 N size 12{3 "." "02" times "10" rSup { size 8{ - 3} } " N"} {}

(b) 1 . 03 × 10 3 size 12{1 "." "03" times "10" rSup { size 8{ - 3} } } {}

What force is needed to pull one microscope slide over another at a speed of 1.00 cm/s, if there is a 0.500-mm-thick layer of 20º C size 12{"20" rSup { size 12{ circ } } C} {} water between them and the contact area is 8.00 cm 2 size 12{8 "." "00"`"cm" rSup { size 8{2} } } {} ?

A glucose solution being administered with an IV has a flow rate of 4 . 00 cm 3 /min size 12{4 "." "00"`"cm" rSup { size 8{3} } "/min"} {} . What will the new flow rate be if the glucose is replaced by whole blood having the same density but a viscosity 2.50 times that of the glucose? All other factors remain constant.

1 . 60 cm 3 /min size 12{1 "." "60 cm" rSup { size 8{3} } "/min"} {}

The pressure drop along a length of artery is 100 Pa, the radius is 10 mm, and the flow is laminar. The average speed of the blood is 15 mm/s. (a) What is the net force on the blood in this section of artery? (b) What is the power expended maintaining the flow?

A small artery has a length of 1 . 1 × 10 3 m size 12{1 "." 1 times "10" rSup { size 8{ - 3} } `m} {} and a radius of 2.5 × 10 5 m size 12{2 "." 5 times "10" rSup { size 8{ - 5} } `m} {} . If the pressure drop across the artery is 1.3 kPa, what is the flow rate through the artery? (Assume that the temperature is 37º C size 12{"37"°C} {} .)

8.7 × 10 11 m 3 /s size 12{8 "." 7 times "10" rSup { size 8{ - "11"} } `m rSup { size 8{3} } "/s"} {}

Fluid originally flows through a tube at a rate of 100 cm 3 /s size 12{"100"`"cm" rSup { size 8{3} } "/s"} {} . To illustrate the sensitivity of flow rate to various factors, calculate the new flow rate for the following changes with all other factors remaining the same as in the original conditions. (a) Pressure difference increases by a factor of 1.50. (b) A new fluid with 3.00 times greater viscosity is substituted. (c) The tube is replaced by one having 4.00 times the length. (d) Another tube is used with a radius 0.100 times the original. (e) Yet another tube is substituted with a radius 0.100 times the original and half the length, and the pressure difference is increased by a factor of 1.50.

Questions & Answers

do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
I'm interested in Nanotube
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Physics 105: adventures in physics. OpenStax CNX. Dec 02, 2015 Download for free at http://legacy.cnx.org/content/col11916/1.1
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