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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?

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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.

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

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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.
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Problems&Exercises

(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} } } {}

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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} } } {} ?

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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"} {}

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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?

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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"} {}

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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.

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Questions & Answers

how can we find absolute uncertainty
ayesha Reply
it what?
Luke
in physics
ayesha
the basic formula is uncertainty in momentum multiplied buy uncertainty In position is greater than or equal to 4×pi/2. same formula for energy and time
Luke
I have this one question can you please look it up it's 9702/22/O/N/17 Question 1 B 3
ayesha
what
uma
would you like physics?
Suthar
yes
farooq
precision or absolute uncertainty is always equal to least count of that instrument
Iram
how do I unlock the MCQ and the Essay?
Ojeh Reply
what is the dimension of strain
Joy Reply
Is there a formula for time of free fall given that the body has initial velocity? In other words, formula for time that takes a downward-shot projectile to hit the ground. Thanks!
Cyclone Reply
hi
Agboro
hiii
Chandan
Hi
Sahim
hi
Jeff
hey
Priscilla
sup guys
Bile
Hy
Kulsum
What is unit of watt?
Kulsum
watt is the unit of power
Rahul
p=f.v
Rahul
watt can also be expressed as Nm/s
Rahul
what s i unit of mass
Maxamed
SI unit of mass is Kg(kilogram).
Robel
what is formula of distance
Maxamed
Formula for for the falling body with initial velocity is:v^2=v(initial)^2+2*g*h
Mateo
i can't understand
Maxamed
we can't do this calculation without knowing the height of the initial position of the particle
Chathu
sorry but no more in science
Imoreh
2 forces whose resultant is 100N, are at right angle to each other .if one of them makes an angle of 30 degree with the resultant determine it's magnitude
Victor Reply
50 N... (50 *1.732)N
Sahim
Plz cheak the ans and give reply..
Sahim
Is earth is an inertial frame?
Sahim Reply
The abacus (plural abaci or abacuses), also called a counting frame, is a calculating tool that was in use in Europe, China and Russia, centuries before the adoption of the written Hindu–Arabic numeral system
Sahim
thanks
Irungu
Most welcome
Sahim
Hey.. I've a question.
Sahim Reply
Is earth inertia frame?
Sahim
only the center
Shii
What is an abucus?
Irungu
what would be the correct interrogation "what is time?" or "how much has your watch ticked?"
prakash Reply
someone please give answer to this.
prakash
a load of 20N on a wire of cross sectional area 8×10^-7m produces an extension of 10.4m. calculate the young modules of the material of the wire is of length 5m
Ebenezer Reply
Young's modulus = stress/strain strain = extension/length (x/l) stress = force/area (F/A) stress/strain is F l/A x
El
so solve it
Ebenezer
please
Ebenezer
two bodies x and y start from rest and move with uniform acceleration of a and 4a respectively. if the bodies cover the same distance in terms of tx and ty what is the ratio of tx to ty
Oluwatola Reply
what is cesium atoms?
prakash Reply
The atoms which form the element Cesium are known as Cesium atoms.
Naman
A material that combines with and removes trace gases from vacuum tubes.
Shankar
what is difference between entropy and heat capacity
Varun
Heat capacity can be defined as the amount of thermal energy required to warm the sample by 1°C. entropy is the disorder of the system. heat capacity is high when the disorder is high.
Chathu
I want learn physics
Vinodhini Reply
sir how to understanding clearly
Vinodhini
try to imagine everything you study in 3d
revolutionary
pls give me one title
Vinodhini
displacement acceleration how understand
Vinodhini
vernier caliper usage practically
Vinodhini
karthik sir is there
Vinodhini
what are the solution to all the exercise..?
What is realm
Vinodhini Reply
The quantum realm, also called the quantum scale, is a term of art inphysics referring to scales where quantum mechanical effects become important when studied as an isolated system. Typically, this means distances of 100 nanometers (10−9meters) or less or at very low temperature.
revolutionary
How to understand physics
Vinodhini Reply
i like physics very much
Vinodhini
i want know physics practically where used in daily life
Vinodhini
I want to teach physics very interesting to studentd
Vinodhini
how can you build interest in physics
Prince
by reading it
Austin
understanding difficult
Vinodhini
vinodhini mam, physics is used in our day to day life in all events..... everything happening around us can be explained in the base of physics..... saying simple stories happening in our daily life and relating it to physics and questioning students about how or why its happening like that can make
revolutionary
your class more interesting
revolutionary
anything send about physics daily life
Vinodhini
How to understand easily
Vinodhini
check out "LMES" youtube channel
revolutionary
even when you see this message in your phone...it works accord to a physics principle. you touch screen works based on physics, your internet works based on physics, etc....... check out google and search for it
revolutionary
what is mean by Newtonian principle of Relativity? definition and explanation with example
revolutionary Reply
Practice Key Terms 5

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Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
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