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[link] shows how viscosity is measured for a fluid. Two parallel plates have the specific fluid between them. The bottom plate is held fixed, while the top plate is moved to the right, dragging fluid with it. The layer (or lamina) of fluid in contact with either plate does not move relative to the plate, and so the top layer moves at v size 12{v} {} while the bottom layer remains at rest. Each successive layer from the top down exerts a force on the one below it, trying to drag it along, producing a continuous variation in speed from v size 12{v} {} to 0 as shown. Care is taken to insure that the flow is laminar; that is, the layers do not mix. The motion in [link] is like a continuous shearing motion. Fluids have zero shear strength, but the rate at which they are sheared is related to the same geometrical factors A size 12{A} {} and L size 12{L} {} as is shear deformation for solids.

The figure shows the laminar flow of fluid between two rectangular plates each of area A. The bottom plate is shown as fixed. The distance between the plates is L. The top plate is shown to be pushed to right with a force F. The direction of movement of the layer of fluid in contact with the top plate is also toward right with velocity v. The fluid in contact with the plate in the bottom is shown to be in rest with v equals zero. As we see through the layers above the one on the bottom plate, each show a small displacement toward right in increasing order of value with the topmost layer showing the maximum.
The graphic shows laminar flow of fluid between two plates of area A size 12{A} {} . The bottom plate is fixed. When the top plate is pushed to the right, it drags the fluid along with it.

A force F size 12{F} {} is required to keep the top plate in [link] moving at a constant velocity v size 12{v} {} , and experiments have shown that this force depends on four factors. First, F size 12{F} {} is directly proportional to v size 12{v} {} (until the speed is so high that turbulence occurs—then a much larger force is needed, and it has a more complicated dependence on v size 12{v} {} ). Second, F size 12{F} {} is proportional to the area A size 12{A} {} of the plate. This relationship seems reasonable, since A size 12{A} {} is directly proportional to the amount of fluid being moved. Third, F size 12{F} {} is inversely proportional to the distance between the plates L size 12{L} {} . This relationship is also reasonable; L size 12{L} {} is like a lever arm, and the greater the lever arm, the less force that is needed. Fourth, F size 12{F} {} is directly proportional to the coefficient of viscosity , η size 12{η} {} . The greater the viscosity, the greater the force required. These dependencies are combined into the equation

F = η vA L , size 12{F=η { { ital "vA"} over {L} } } {}

which gives us a working definition of fluid viscosity     η size 12{η} {} . Solving for η size 12{η} {} gives

η = FL vA , size 12{F=η { { ital "FL"} over { ital "vA"} } } {}

which defines viscosity in terms of how it is measured. The SI unit of viscosity is N m/ [ ( m/s ) m 2 ] = ( N/m 2 ) s or Pa s size 12{N cdot "m/" \[ \( "m/s" \) m rSup { size 8{2} } \] = \( "N/m" rSup { size 8{2} } \) "sorPa" cdot s} {} . [link] lists the coefficients of viscosity for various fluids.

Viscosity varies from one fluid to another by several orders of magnitude. As you might expect, the viscosities of gases are much less than those of liquids, and these viscosities are often temperature dependent. The viscosity of blood can be reduced by aspirin consumption, allowing it to flow more easily around the body. (When used over the long term in low doses, aspirin can help prevent heart attacks, and reduce the risk of blood clotting.)

Laminar flow confined to tubes—poiseuille’s law

What causes flow? The answer, not surprisingly, is pressure difference. In fact, there is a very simple relationship between horizontal flow and pressure. Flow rate Q size 12{Q} {} is in the direction from high to low pressure. The greater the pressure differential between two points, the greater the flow rate. This relationship can be stated as

Q = P 2 P 1 R , size 12{Q= { {P rSub { size 8{2} } - P rSub { size 8{1} } } over {R} } } {}

where P 1 size 12{P rSub { size 8{1} } } {} and P 2 size 12{P rSub { size 8{2} } } {} are the pressures at two points, such as at either end of a tube, and R size 12{R} {} is the resistance to flow. The resistance R size 12{R} {} includes everything, except pressure, that affects flow rate. For example, R size 12{R} {} is greater for a long tube than for a short one. The greater the viscosity of a fluid, the greater the value of R size 12{R} {} . Turbulence greatly increases R size 12{R} {} , whereas increasing the diameter of a tube decreases R size 12{R} {} .

Questions & Answers

what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
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
Daniel
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
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
How can I make nanorobot?
Lily
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
how can I make nanorobot?
Lily
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
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.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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.
Tarell
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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