These slides are useful for both civil and mechanical diploma ,engineering students

1. Shri. V.B.Amargol
B.E (Civil)
Lecturer

2. Fluid Mechanics :- It is a branch of Science which
deals with the study regarding the behavior of fluids
at rest or in motion.
Hydraulics :- It is a branch of fluid mechanics which
deals with study regarding the behavior of water etheir
in rest or in motion.

3. SL.NO LIQUIDS GASES
1 Liquids are compressible Gases are readily compressible
2 Liquids Can’t expand Gases can expand to fill any
volume
3 Liquids have definite volume Gases don’t have definite volume
4 It’s properties don’t affects due to
change in temperature
Properties get affected due to
change in temperature
5 Liquids form free surface in
gravitational field
Gases don’t form free surface

4. Following are the important properties of Liquids.
1) Mass Density or Density :- It is the ratio of mass
per unit volume at standard temperature &
pressure.
it is denoted by ʃ & its unit is Kg/m3
ʃ = m/v
Mass density of water is 1000 Kg/m3

5. 2) Specific Weight or Weight density :- It is defined
as weight per unit volume at standard
temperature & pressure.
It is denoted by “w”
Therefore w= Weight/volume
= mass X g/Volume
w= ʃ x g
Its unit is Kn/m3
The specific weight if water is 9.81 Kn/m3

6. 3)Specific Gravity :- It is the ratio of specific weight of
liquid to the specific weight of water.
It is denoted by “ s ”
Specific gravity = s = Sp. Wt of liquid / Sp. Wt of water
It has no unit.
The Sp. gr of water is 1 & Sp. gr of mercury is 13.6
4) Viscosity :- It is resisting property of the fluid against
the shearing force. It resist one layer over the another
layer.
it is denoted by “Ʈ”
Its unit is N.s/m2

7. 5) Compressibility :- It is the property of fluid by virtue
of which fluid undergoes change in volume under the
action of external pressure is known as compressibilty.
Its is denoted by “K”
K = Compressive stress / volumetric strain
6) Surface tension :- It is the property of liquid which
enables it to resist tensile stress which may be cohesive
or adhesive.

8. 7) Capillarity :- It is the phenomenon by which the
liquid rises or falls into a thin glass tube when it
is dipped into liquid.
It rises when tube is dipped into water.
It falls when tube is dipped into mercury.

9. 8) Vapor pressure :- Liquid evaporates at room
temperature. If the liquid is kept in a closed vessel it
evaporates & the vapor occupies the space above the
liquid surface. This vapor applies a pressure on the
surface of the liquid. This pressure is called vapor
pressure.
9) Specific Volume:- The volume occupied by unit mass
is called Specific volume.
Specific volume is reciprocal of density. It is denoted by
“ v ” therefore v = Vol / mass
Its unit is m3 / Kg

10. When a fluid is contained in a vessel it exerts force at all
points on the sides & at the bottom of container, the
direction force is normal to the surface.
Fluid pressure is the force per unit area
Pressure , p = F / A
The unit of pressure is kilo pascal or N/mm2
The fig shows different shapes of
containers which is filled with same
liquid , even though the shape is
different it exerts same pressure at a
particular depth of liquid.
therefore
intensity pressure = p = w X h
& pressure head = h = p / w

11. The pressure at any point on the earth surface depends
upon height of air column above it. The pressure is
measured with reference to some arbitrary datum.
The different types of pressures are
1) Atmospheric pressure:- The air & other gases
possess weight & hence it must exert some intensity of
pressure.
the weight of air column above unit area of earth’s
surface is called atmospheric pressure. It varies with
the height. It measured by Barometer.
Atmospheric Pressure = 101.3 kn/m2 or 101.3 Kpa
= 10.33 metres of water
= 760 mm of mercury

12. 2)Absolute Pressure :- When the pressure is
measured above the absolute zero as a datum,
then the pressure is called absolute pressure.
3) Gauge Pressure : - When the pressure is
measured above or below the atmospheric
pressure, then such a pressure is called Gauge
pressure. It is measured with the help of pressure
measuring devices in which the atmospheric
pressure is taken as datum.
4) Vacuum pressure :- The pressure of the fluid
below the atmospheric pressure is know as
vacuum pressure.

13. The relation between absolute pressure, gauge pressure &
Vacuum pressure is as follows.
Absolute Pressure = Atmospheric Pressure + Gauge Pressure

14. The pressure of the fluid is measured by the following
devices.
1) Manometer
2) Mechanical Gauges
1) Manometers :- Manometers are the devices which
are used for measuring the pressure of a fluid at a
point by balancing the another of fluid.
The manometers classified as
a) Piezometer (b) U-tube manometer (c)Differential
manometer

15. a) Piezometer :- Piezometer is the simplest form os
manometer used for measuring low pressure of
liquids. It consists of a glass tube whose one end is
connected to a point where pressure is to be
measured & other end remains open to atmosphere
as shown below.
The pressure at any point in the
liquid is determined by the
height of the liquid in the
tube above that point.
Pressure at a point ‘A’ = p = wh
Where, w = Sp.wt of liquid
h = Ht of liquid column.

16. b) U-Tube Manometer :- It consists of U shape glass
tube whose one end is connected to a point where
pressure is to be measured & the other end
remains open to atmosphere as shown below.
The tube contains mercury whose Sp.gr is 13.6.
the positive gauge pressure of the manometer is
given by
h = h2s2 – h1s1 mtr of water

17. For negative gauge pressure of the manometer
h = -(h1s1 +h2s2) mtr of water
c) Differential manometer :- It is used to measure
the pressure difference between two points of the
same pipe or different pipe. The manometer
consist of a U-tube containing mercury.
The difference of pressure between the two points
is calculated by using the formula
hA – hB = h(s-s1) mtr of water

18. Advantages of Manometer :-
1) Manometers have good accurcy.
2) These are not affected by vibration.
3) They are easy to fabricate.
4) They are inexpensive.
5) They have high sensitivity.
6) They requires less maintenance.
7) They are suitable for low pressure.

19. Difference between Simple manometer &
Differential Manometer
Sl.No Simple manometer Differential manometer
1 One limb is connected to the
point & another is open to air.
Both limbs are connected to
the points
2 It is used to measure pressure at a
point .
It is used to measure
pressure between two
points.
3 The pressure at a point is
obtained in terms of difference of
level of fluid flowing in the pipe.
The difference of pressure is
obtained in terms of
difference of levels of
manometric liquid.
4 It can be manometers like
piezometer or U-tube
manometer.
It can be manometer like
Differential U-tube.

20. When the lamina or body is immersed in
fluid, it exerts a pressure on the body which
depends upon the depth of immersion, area of
body & specific weight of fluid. The whole pressure
will act at a single point on the body. So we have to
calculate the total pressure on the body & the
position of center of pressure.

21. Total Pressure :- It is defined as the force exerted by a
static fluid on a surface either plane or curved, when the
fluid makes contact with the surface. It is always
perpendicular to the surface.
Total pressure P = wAẌ
Where , W = Sp.wt of liquid
A = Area of lamina ,
Ẍ = Depth of center of gravity of area from free liquid
surface.
Center of Pressure :- It is a point on the immersed surface
at where the resultant of all the hydrostatic pressure acts.
It is expressed in terms of depth from the free liquid
surface.
Depth of center pressure = Ћ = (IG / AẌ) + Ẍ