Viscosity
: It is the property of the fluid which opposes the relative motion
between the two surfaces of the fluid in a fluid that are moving a
different velocity.
Viscosity can be two types:
1: Dynamic Viscosity Or Absolute Viscosity Or Coefficient of Viscosity or Viscosity
2: Kinematic Viscosity ( This is imaginary not really present in real life)
The main difference between Dynamic viscosity and Kinematic Viscosity is:
Dynamic
Viscosity: One way is to measure a fluid's resistance to flow when an
external force is applied , This is Dynamic viscosity , always it is
used for practical purpose.
Units: SI : N.S/ m2
C.G.S Unit: Dyne-Sec/ Cm2 ( It is also called Poise)
M.K.S. Unit: Kgf-Sec/ m2
Kinematic
Viscosity: The other way is to measure the resistive flow of a fluid
under the weight of gravity , the result is kinematic vicosity . Do not
use it by your own, until there is no mention of particulate word
(Kinematic Viscosity) in numerical .
Units: SI : m2/s
CGS unit: cm2/sec ( It is called stoke )
M.K.S =m2/Sec
IMP Point:-
Two
fluid that have the same Dynamic viscosity can have different kinematic
viscosity This is due to kinematic viscosity dependent on the density
of the fluid , density is not a factor with Dynamic viscosity .
Some Other Key Points regarding Viscosity:
1: The dynamic viscosity of pure water at 20 degree Celsius is 0.01 poise or 1 centi poise
2:
The viscosity of fluid decreases with increasing the temperature (
Because fluid has a tendency to flow in stream line in most of the cases
, when velocity of flow is low)
3: The viscosity of
gases increases with increasing the temperature ( REASON: when we heat
the gases then gas molecules travel in zig zag motion, so the momentum
of gases particles increases and they generate high shear stress due to
high momentum)
4: Water has higher viscosity than Mercury.
Now test youself : MCQ : based on Viscosity:
Q1: Poise is the C.G.S unit of:
A: Viscosity
B: Kinematic Viscosity
C: Surface Tension
D: Capillary
Q2: C.G.S unit of Kinematic Viscosity is:
A: Newton-Sec
B: Stoke
C: Dyne
D: Poise
Q3: The increase of the temperature :
A: Increase the viscosity of liquid
B Increase the viscosity of gases
C: Decrease the viscosity of gases
D: No effect
Q4: Newton law of viscosity states that :
A: shear stress is directly proportional to the velocity
B: Shear stress is directly proportional to velocity
C: shear stress is directly proportional to rate of shear strain
D: Shear stress is directly proportional to the viscosity
Q5: Which has higher viscosity : A : Mercury,
B: Water
Q6: What measures a material's resistance to flow?
A: Matter , B: Volume
C: Viscosity, D: Surface Tension
Q7: When friction increases what else increases? A: Elasticity , B: Density , C: Viscosity, D: Matter
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