This chapter introduces concepts related to fluid mechanics including definitions, properties, and units. It defines a fluid as a substance that flows under shear stress and can be a liquid or gas. Properties like density, specific weight, viscosity, and specific gravity are discussed. Density is defined as mass per unit volume and varies between different fluids. Viscosity describes a fluid's resistance to flow and can vary significantly between fluids. Finally, it distinguishes between Newtonian and non-Newtonian fluids based on whether viscosity depends on shear rate.

1. Chapter 1 -Chapter 1 -
A PowerPoint Presentation byA PowerPoint Presentation by
NOOR ASSIKIN BINTI ABD WAHABNOOR ASSIKIN BINTI ABD WAHAB
© 2011

2. IntroductionIntroduction
 This chapter will begin with several concepts,This chapter will begin with several concepts,
definition, terminologies and approaches whichdefinition, terminologies and approaches which
should be understood by the students beforeshould be understood by the students before
continuing reading the rest of this module.continuing reading the rest of this module.
 Then, it introduces the student with typicalThen, it introduces the student with typical
properties of fluid and their dimensions which areproperties of fluid and their dimensions which are
then being used extensively in the next chaptersthen being used extensively in the next chapters
and units like pressure, velocity, density andand units like pressure, velocity, density and
viscosity.viscosity.
 Some of these can be used to classify type andSome of these can be used to classify type and
characteristic of fluid, such as whether a fluid ischaracteristic of fluid, such as whether a fluid is
incompressible or not or whether the fluid isincompressible or not or whether the fluid is
Newtonian or non-NewtonianNewtonian or non-Newtonian..

3. Fluid ConceptFluid Concept
• Fluid mechanics is a division inFluid mechanics is a division in appliedapplied
mechanics related to the behaviour of liquidmechanics related to the behaviour of liquid
or gas which is either in rest or in motion.or gas which is either in rest or in motion.
• The study related to a fluid in rest orThe study related to a fluid in rest or
stationary is referred tostationary is referred to fluid staticfluid static,,
otherwise it is referred to asotherwise it is referred to as fluid dynamicfluid dynamic..
• Fluid can be defined as a substance whichFluid can be defined as a substance which
can deform continuously when beingcan deform continuously when being
subjected to shear stress at any magnitudesubjected to shear stress at any magnitude..
In other words, it can flow continuously asIn other words, it can flow continuously as
a result of shearing action. This includesa result of shearing action. This includes
any liquid or gas.any liquid or gas.

4. DEFINE FLUIDSDEFINE FLUIDS
(a) Solid (b) Liquid (c) Gas
k
kk
k
Free surface

5.  For solid, imagine that the molecules can beFor solid, imagine that the molecules can be
fictitiously linked to each other with springs.fictitiously linked to each other with springs.
• In fluid, the molecules can move freely but areIn fluid, the molecules can move freely but are
constrained through a traction force calledconstrained through a traction force called
cohesioncohesion.. This force is interchangeable from oneThis force is interchangeable from one
molecule to anothermolecule to another..
• For gases, it is very weak which enables the gas toFor gases, it is very weak which enables the gas to
disintegrate and move away from its container.disintegrate and move away from its container.
 For liquids, it is stronger which is sufficient enoughFor liquids, it is stronger which is sufficient enough
to hold the molecule together and can withstandto hold the molecule together and can withstand
high compression, which is suitable for applicationhigh compression, which is suitable for application
as hydraulic fluid such as oil. On the surface, theas hydraulic fluid such as oil. On the surface, the
cohesion forms a resultant force directed into thecohesion forms a resultant force directed into the
liquid region and the combination of cohesionliquid region and the combination of cohesion
forces between adjacent molecules from aforces between adjacent molecules from a
tensioned membrane known astensioned membrane known as free surfacefree surface..

6. Definition of a FluidDefinition of a Fluid
A fluid is a substance that flows under the action of
shearing forces. If a fluid is at rest, we know that the
forces on it are in balance.
A gas is a fluid that is easily compressed. It fills any
vessel in which it is contained.
A liquid is a fluid which is hard to compress. A
given mass of liquid will occupy a fixed volume,
irrespective of the size of the container.
A free surface is formed as a boundary between a
liquid and a gas above it.

7. Fluid PropertiesFluid Properties
• Define “characteristics” of a specific fluidDefine “characteristics” of a specific fluid
•Properties expressed by basic “dimensions”Properties expressed by basic “dimensions”
– length, mass (or force), time, temperaturelength, mass (or force), time, temperature
• Dimensions quantified by basic “units”Dimensions quantified by basic “units”
We will consider systems of units, important fluidWe will consider systems of units, important fluid
properties (not all), and the dimensions associated withproperties (not all), and the dimensions associated with
those properties.those properties.

8. System International (SI)System International (SI)
• Length = meters (m)Length = meters (m)
• Mass = kilograms (kg)Mass = kilograms (kg)
• Time = second (s)Time = second (s)
• Force = Newton (N)Force = Newton (N)
– Force required to accelerate 1 kg @ 1 m/sForce required to accelerate 1 kg @ 1 m/s22
– Acceleration due to gravity (g) = 9.81 m/sAcceleration due to gravity (g) = 9.81 m/s22
– Weight of 1 kg at earth’s surface = W = mg = 1 kg (9.81Weight of 1 kg at earth’s surface = W = mg = 1 kg (9.81
m/sm/s22
) = 9.81 kg-m/s) = 9.81 kg-m/s22
= 9.81 N= 9.81 N
• Temperature = Kelvin (Temperature = Kelvin (oo
K)K)
– 273.15273.15 oo
K = freezing point of waterK = freezing point of water
– oo
K = 273.15 +K = 273.15 + oo
CC

9. System International (SI)System International (SI)
• Work and energy = Joule (J)Work and energy = Joule (J)
J = N*m = kg-m/sJ = N*m = kg-m/s22
* m = kg-m* m = kg-m22
/s/s22
• Power = watt (W) = J/sPower = watt (W) = J/s
• SI prefixes:SI prefixes:
G = giga = 10G = giga = 1099
c = centi = 10c = centi = 10-2-2
M = mega = 10M = mega = 1066
m = milli = 10m = milli = 10-3-3
k = kilo = 10k = kilo = 1033
µµ = micro = 10= micro = 10-6-6

10. DensityDensity
• Mass per unit volume (e.g., @ 20Mass per unit volume (e.g., @ 20 oo
C, 1 atm)C, 1 atm)
– WaterWater ρρwaterwater = 1,000 kg/m= 1,000 kg/m33
(62.4 lbm/ft(62.4 lbm/ft33
))
– MercuryMercury ρρHgHg = 13,500 kg/m= 13,500 kg/m33
– AirAir ρρairair = 1.205 kg/m= 1.205 kg/m33
• Densities of gases = strong f (T,p) =compressibleDensities of gases = strong f (T,p) =compressible
• Densities of liquids are nearly constantDensities of liquids are nearly constant
(incompressible) for constant temperature(incompressible) for constant temperature
• Specific volume = 1/density = volume/massSpecific volume = 1/density = volume/mass

11. DensityDensity
The density of a fluid is defined as its mass per
unit volume. It is denoted by the Greek
symbol, ρ.
ρ =
V m3
kgm-3
If the density is constant (most liquids), the flow is
incompressible.
If the density varies significantly (eg some gas flows), the
flow is compressible.
(Although gases are easy to compress, the flow may be treated
as incompressible if there are no large pressure fluctuations)
ρ water= 998 kgm-3
ρair =1.2kgm-3
kg
m

12. Mass DensityMass Density
2 kg, 4000 cm3
Wood
177 cm3
45.2 kg
;
mass m
Density
volume V
ρ= =
Lead: 11,300 kg/mLead: 11,300 kg/m33
Wood: 500 kg/mWood: 500 kg/m33
4000 cm3
Lead
Same volume
2 kg
Lead
Same mass

13. Example 1:Example 1: The density of steel isThe density of steel is 7800 kg/m7800 kg/m33
..
What is the volume of aWhat is the volume of a 4-kg4-kg block of steel?block of steel?
4 kg
3
4 kg
;
7800 kg/m
m m
V
V
ρ
ρ
= = =
V = 5.13 x 10-4
m3V = 5.13 x 10-4
m3
What is the mass if the volume is 0.046 m3
?
3 3
(7800 kg/m )(0.046 m );m Vρ= =
m = 359 kgm = 359 kg

14. Specific WeightSpecific Weight
]/[]/[ 33 ftlbformNgργ =
• Weight per unit volume (e.g., @ 20Weight per unit volume (e.g., @ 20 oo
C, 1 atm)C, 1 atm)
γγwaterwater = (998 kg/m= (998 kg/m33
)(9.807 m)(9.807 m22
/s)/s)
= 9,790 N/m= 9,790 N/m33
[= 62.4 lbf/ft[= 62.4 lbf/ft33
]]
γγairair = (1.205 kg/m= (1.205 kg/m33
)(9.807 m)(9.807 m22
/s)/s)
= 11.8 N/m= 11.8 N/m33
[= 0.0752 lbf/ft[= 0.0752 lbf/ft33
]]

15. Specific GravitySpecific Gravity
Ratio of fluid density to density of water @ 4o
C
3
/1000 mkg
SG
liquid
water
liquid
liquid
ρ
ρ
ρ
==
Water SGwater = 1
Mercury SGHg = 13.55
Note: SG is dimensionless and independent of system of units

16. Specific GravitySpecific Gravity
The specific gravity (or relative density) of a
material is the ratio of its density to the density of
water (1000 kg/m3
).
Steel (7800 kg/m3
) ρr = 7.80
Brass (8700 kg/m3
) ρr = 8.70
Wood (500 kg/m3
) ρr = 0.500
Steel (7800 kg/m3
) ρr = 7.80
Brass (8700 kg/m3
) ρr = 8.70
Wood (500 kg/m3
) ρr = 0.500
Examples:Examples:
3
1000 kg/m
x
r
ρ
ρ =

17. viscosity in fluid flowsviscosity in fluid flows

18. ViscosityViscosity
• Viscosity,Viscosity, µµ,, is a measure of resistance to fluid flow as ais a measure of resistance to fluid flow as a
result of intermolecular cohesion. In other words, viscosityresult of intermolecular cohesion. In other words, viscosity
can be seen as internal friction to fluid motion which cancan be seen as internal friction to fluid motion which can
then lead to energy loss.then lead to energy loss.
• Different fluids deform at different rates under the sameDifferent fluids deform at different rates under the same
shear stress. The ease with which a fluid pours is anshear stress. The ease with which a fluid pours is an
indication of its viscosity. Fluid with a high viscosity such asindication of its viscosity. Fluid with a high viscosity such as
syrup deforms more slowly than fluid with a low viscositysyrup deforms more slowly than fluid with a low viscosity
such as water. The viscosity is also known as dynamicsuch as water. The viscosity is also known as dynamic
viscosity.viscosity.
 Units:Units: N.s/m2 or kg/m/sN.s/m2 or kg/m/s
 Typical values:Typical values:
Water = 1.14x10-3 kg/m/s; Air = 1.78x10-5 kg/m/sWater = 1.14x10-3 kg/m/s; Air = 1.78x10-5 kg/m/s

19. ViscosityViscosity
• Proportionality constant = dynamic (absolute)Proportionality constant = dynamic (absolute)
viscosityviscosity
• Newton’s Law of ViscosityNewton’s Law of Viscosity
• ViscosityViscosity
• UnitsUnits
• Water (@ 20Water (@ 20oo
C):C): µµ = 1= 1xx1010-3-3
N-s/mN-s/m22
• Air (@ 20Air (@ 20oo
C):C): µµ = 1.8= 1.8xx1010-5-5
N-s/mN-s/m22
• Kinematic viscosityKinematic viscosity
V
V+d
v
dy
dV
µτ =
dydV /
τ
µ =
2
2
//
/
m
sN
msm
mN ⋅
=
ρ
µ
ν =
Kinematic viscosity: m2
/s
1 poise = 0.1 N-s/m2
1 centipoises = 10-2
poise = 10-3
N-s/m2

20. Newtonian and Non-NewtonianNewtonian and Non-Newtonian
FluidFluid
Example:
Air
Water
Oil
Gasoline
Alcohol
Kerosene
Benzene
Glycerine
Newton’s’ law of viscosity is given by;
dy
du
µ=τ
(1.1)
τ = shear stress
µ = viscosity of fluid
du/dy = shear rate, rate of strain or velocity gradient
• The viscosity µ is a function only of the condition of the fluid, particularly its
temperature.
• The magnitude of the velocity gradient (du/dy) has no effect on the magnitude of µ.