This document provides information about fluid mechanics concepts and units of measurement. It begins by acknowledging the sources of the lecture notes. It then defines key concepts like pressure, density, viscosity, stress, and flow and provides conversion factors between common unit systems. Diagrams are included to illustrate concepts like laminar flow and shear stress. Overall, the document serves as a reference for fluid mechanics terminology, equations, and units.

2. 2
Giving credit where credit is due:
 Most of the lecture notes are based on the
slides from the course notes available to
students,
 Some slides are from Different Website related
to the same subjects,
 I have modified them and added new slides.
Fluid Mechanics (CV 215)

3. 101.3 kPa
14.7 psi
760mm Hg
34 ft of water
1.013 bar
Standard Atmosphere


Zero absolute pressure Pabsolute = 0
Zero atmospheric pressure Pgage = 0
P(A) absolute
P(A) gage
P(B) gage
P(B) absolute
A
B

4. English Units
SI Units
Dimensions
Quantity
Foot ft
Meter m
L
Length “L”
Slug slug
Kilogram kg
M
Mass “M”
Second sec
Second s
T
Time “t”
radian rad
Kelvin k

Temperature “T”
Basic Dimensions and their Units

5. English Units
SI Units
Dimension
Quantity
ft2
m2
L2
Area A
ft3
m3
L3
Volume V
ft/sec
m/s
L/T
Velocity V
ft2/s
m2/ s
L2/ T
Acceleration a
Ibf/ft2
N/m2 or Pa
M/LT2
Pressure P
Ibf/ft2
N/m2 or Pa
M/LT2
Stress 
Ibf/ft
N/m
M/T2
Surface tension 
ft . Ib
N.M or J
ML2/T2
Work W
ft . Ib
N. m or J
ML2/T2
Energy E
ft . Ib
N. m
ML2/T2
Torque T
ft3/sec
m3/s
L3/T
Flow rate Q
Derived Dimensions and their Units

6. English Units
SI Units
Dimension
Quantity
Ibf/ft2
N/m2 or Pa
M/LT2
Stress 
Ibf/ft
N/m
M/T2
Surface tension 
ft . Ib
N.M or J
ML2/T2
Work W
Ibf . sec /ft2
N . s /m2
M/LT
Viscosity 
ft2/sec
m2/s
L2/T
Kinematic viscosity 
sec-1
s-1
T-1
Angular velocity 
Slug .ft /sec2 or Ib
Kg .m/sec2or N
M L /T2
Force F
slug /ft3
kg /m 3
M /L3
Density
Ib/ft3
N/m3
M/L2 T2
Specific weight
Derived Dimensions and their Units

7. (Multiple x  )
 Prefix
Standard Prefix in SI Units
Napo,
n
micro,

milli,
m
centi,
C
deci, d
deka,
da
hecoto,
h
Kilo,
K
Mega,
M
Giga,
G
10-9
10-6
10-3
10-2
10-1
101
102
103
106
109



8. Weight: is the amount that a body of fluid
weights, that is, the force with which the
fluid is attracted toward earth by .We use
the symbol (W) for weight.
Mass: is the property of a body of fluid that is a
measure of its inertia or resistance to a
change in motion. It is also a measure of the
quantity of fluid. We use the symbol (m) for
mass.
Mass and Weight

9. N Ibf kgf
g

81
9
1000
. g
6
453.
 g
1000

1
Relative Magnitude of the Force Units
Newton (N), pound-force (Ibf), and Kilogram-force (Kgf)
5 10

10. M = 1.0 kg
M = 32.2 Ibm (Slug)
2
s
/
m
a 

2
s
/
ft
a 

F = 1.0 N
F = 1.0 Ibf
The relationship between force and mass, F =m  a,
Where “ a” is the acceleration expressed in units of m/s2 or ft /sec2.

11.  When we speak of weight, W, we imply that the
acceleration is equal to, “g”, the acceleration due to
gravity. Then the Newton’s Law becomes,
W= m  g
 In this study, we will use:
g =9.81 m/s2 (SI System)
and
g =32.2 ft/sec2 (English System)

12. kg Ibm
2
/
81
.
9 s
m
g 
2
sec
/
2
.
32 ft
g 
f
2
kg
0
.
1
N
81
.
9
s
/
m
.
kg
81
.
9
W



f
2
m
Ib
0
.
1
)
ses
/
ft
(
Ib
2
.
32
W




13. Solid, Fluid and
Gas

14. A Solid can resist a shear stress by a static deflection
A Fluid
being composed of relatively closed-packed
molecules with strong cohesive forces, tends
to retain its volume and will form a free
surface.
A Gas
The gas is unrestrained and expands out of the
Container, filling all available spaces.

15. In hydraulics, it is useful to know which direction water
is moving and so the term velocity is used instead of
speed. When an object travels a known distance and
the time taken to do this is also known, then the
velocity can be calculated as follows:
(s)
Time
m)
distance (
)
s
/
m
(
V 
Velocity and Accelerations

16.  Acceleration describes change in velocity. When
an object's velocity is increasing then it is
accelerating; when it is slowing down it is
decelerating. Acceleration is measured in
meters/second (m/s2). If the initial and final
velocities are known as well as the time taken for
the velocity to change then the acceleration can
be calculated as follows:
(s)
Time
(m/s)
velocity
in
Change
)
s
/
m
(
on
Accelerati 2


17.  Acceleration describes change in velocity. When an
object's velocity is increasing then it is accelerating;
when it is slowing down it is decelerating.
Acceleration is measured in meters/second2 (m/s2).
If the initial and final velocities are known as well as
the time taken for the velocity to change then the
acceleration can be calculated as follows:
(s)
Time
(m/s)
velocity
in
Change
)
s
/
m
(
on
Accelerati 2


19.  Mass density of any material is the mass of one cubic meter
of the material and is a fixed value for the material
concerned.
 Mass density is usually denoted by the Greek letter (rho).
 Density (M/L3) = mass (M)/ volume (L3)
 For water: the mass of one cubic meter of water is 1000 kg
and so: w= 1000 kg/m3, and
 weight density =1000 9.81
= 9810 N/m3 (or 9.81 kN/m3)
= 10 kN/m3 (approximately)
Mass Density “”

20. Spec. gravity (SG) = density of a substance (M/L3)
density of water (M/L3)
 It is the ratio of the density of a substance to the density of some
standard substance at a specified temperature – usually water- .. It
can be written both in terms of the mass density and the weight
density.
 Note that specific gravity has no dimensions (dimensionless). As the
volume is the same for both the object and the water, another way of
writing this formula is in terms of weight:
 Specific Gravity: is usually denoted by SG or sg.
Specific Gravity “SG & sg”

21.  Specific gravity = weight of an object__________
weight of an equal volume of water
Some useful specific gravity values are included in the following
table:
Comments
S. g
Fluid
All other specific gravity measurements are
made relative to that of water.
1.00
Water
Less than 1.0 and so it floats on water.
0.90
Oil
Important in sediment transport problems.
2.65
Sand
Fluid used in manometers for measuring
pressure.
13.60
Mercury
More than 1.0 and so it sinks in water.
19.20
Gold

22.  Kinematic viscosity: It is denoted by the Greek letter (nu).
 Viscosity and mass density go together and so they are often
combined into a term known as the Kinematic viscosity and is
calculated as follows:
Kinematic viscosity ()= Viscosity ()
Density ()
 For water:  = 1.1410-2 m2/s at a temperature of 15oC
Sometimes Kinematic viscosity is measured in Stokes in
of the work of Sir G. Stokes.
104 Stokes= 1 m2/s
 For water:  =1.14 10-2 Stokes
Kinematic Viscosity “”

23. Shear Stress
The graphic shows laminar flow of fluid between two plates of area “A”

24.  Shear force is increased or decreased in direct
proportion to increase or decrease of relative velocity.
Shear stress has units of N / m2,
Dynamic viscosity has units of
Viscosity has units of
    2
2
m
s
.
N
m
s
m
1
m
N
y
d
V
d






1
2
2
4
2
s
.
m
s
.
N
m
m
s
.
N 







4
2
2
3
m
m
S
N
m
1
m
s
N
m
kg 















25. )
s
.
m
(
kg
or
s
.
P
&
m
/
s
.
N a
2
)
s
.
ft
(
slu g
o r
,
ft
/
s
.
Ib 2
s
.
P
1
.
0
)
s
.
cm
(
g
cm
/
s
.
dyne
poise a
2



The Dynamic Viscosity Units in the three most widely used systems:
S I. System
B.G System
C.g.s System