PPT: Fluid Statics | Fluid Mechanics for Mechanical Engineering PDF Download

 Page 1


Fluid Statics
2

 Fluid Statics: It is the branch of fluid mechanics that deals 
with the behavior/response of fluid when they are at rest. 

 Pressure, (average pressure intensity): It is the normal force 
exerted per unit area. It is denoted by P and is given by;

 Units

 SI: N/m
2
(called Pascal)

 BG: lb/ft
2
or lb/in
2
(called psi)

 CGS: dyne/cm
2
1 bar=10
5
N/m
2
=10
5
Pascal
A
F
area
force
P = =
Page 2


Fluid Statics
2

 Fluid Statics: It is the branch of fluid mechanics that deals 
with the behavior/response of fluid when they are at rest. 

 Pressure, (average pressure intensity): It is the normal force 
exerted per unit area. It is denoted by P and is given by;

 Units

 SI: N/m
2
(called Pascal)

 BG: lb/ft
2
or lb/in
2
(called psi)

 CGS: dyne/cm
2
1 bar=10
5
N/m
2
=10
5
Pascal
A
F
area
force
P = =
Pressure vs Water depth/height
3

 Consider a strip or column of a cylindrical fluid,

 h= height or depth of strip of fluid

 ?= specific weight of fluid

 dA=cross-sectional area of strip

 dV=volume of strip

 dW=weight of strip

 Pressure at base of strip=dF/dA=dW/dA

 P= ?dV/dA

 P= ?dA.h/dA
P=?h
h
Page 3


Fluid Statics
2

 Fluid Statics: It is the branch of fluid mechanics that deals 
with the behavior/response of fluid when they are at rest. 

 Pressure, (average pressure intensity): It is the normal force 
exerted per unit area. It is denoted by P and is given by;

 Units

 SI: N/m
2
(called Pascal)

 BG: lb/ft
2
or lb/in
2
(called psi)

 CGS: dyne/cm
2
1 bar=10
5
N/m
2
=10
5
Pascal
A
F
area
force
P = =
Pressure vs Water depth/height
3

 Consider a strip or column of a cylindrical fluid,

 h= height or depth of strip of fluid

 ?= specific weight of fluid

 dA=cross-sectional area of strip

 dV=volume of strip

 dW=weight of strip

 Pressure at base of strip=dF/dA=dW/dA

 P= ?dV/dA

 P= ?dA.h/dA
P=?h
h
Pressure vs Water depth/height
4

 P=?h

 P a h

 For h=0, P=0

 For h=h, P=?h
h
Pressure distribution 
diagram/pressure profile

 As you know atmospheric pressure reduces, as we move to 
higher elevations.  Is it because of h, as h reduces, P also reduces.
Page 4


Fluid Statics
2

 Fluid Statics: It is the branch of fluid mechanics that deals 
with the behavior/response of fluid when they are at rest. 

 Pressure, (average pressure intensity): It is the normal force 
exerted per unit area. It is denoted by P and is given by;

 Units

 SI: N/m
2
(called Pascal)

 BG: lb/ft
2
or lb/in
2
(called psi)

 CGS: dyne/cm
2
1 bar=10
5
N/m
2
=10
5
Pascal
A
F
area
force
P = =
Pressure vs Water depth/height
3

 Consider a strip or column of a cylindrical fluid,

 h= height or depth of strip of fluid

 ?= specific weight of fluid

 dA=cross-sectional area of strip

 dV=volume of strip

 dW=weight of strip

 Pressure at base of strip=dF/dA=dW/dA

 P= ?dV/dA

 P= ?dA.h/dA
P=?h
h
Pressure vs Water depth/height
4

 P=?h

 P a h

 For h=0, P=0

 For h=h, P=?h
h
Pressure distribution 
diagram/pressure profile

 As you know atmospheric pressure reduces, as we move to 
higher elevations.  Is it because of h, as h reduces, P also reduces.
PASCAL’S LAW
5

 “Pressure at any point in fluid is same in all directions when 
the fluid is at rest”

 Consider a wedge shape element of fluid 
having dimension dx, dy and dz along x, y 
and z axis.

 dl= dimension of inclined plane making 
an angle a with the vertical

 Px, Py, Pz and P are pressure acting in x, y, 
z and perpendicular to inclined surface

 dW=weight of element
z
y
x
Py(dxdz)
Px(dydz)
P(dldz)
dx
dy
dz
a
a
a
P(dldz)
cosa
P(dldz)
sina
dW
z
y
x
Page 5


Fluid Statics
2

 Fluid Statics: It is the branch of fluid mechanics that deals 
with the behavior/response of fluid when they are at rest. 

 Pressure, (average pressure intensity): It is the normal force 
exerted per unit area. It is denoted by P and is given by;

 Units

 SI: N/m
2
(called Pascal)

 BG: lb/ft
2
or lb/in
2
(called psi)

 CGS: dyne/cm
2
1 bar=10
5
N/m
2
=10
5
Pascal
A
F
area
force
P = =
Pressure vs Water depth/height
3

 Consider a strip or column of a cylindrical fluid,

 h= height or depth of strip of fluid

 ?= specific weight of fluid

 dA=cross-sectional area of strip

 dV=volume of strip

 dW=weight of strip

 Pressure at base of strip=dF/dA=dW/dA

 P= ?dV/dA

 P= ?dA.h/dA
P=?h
h
Pressure vs Water depth/height
4

 P=?h

 P a h

 For h=0, P=0

 For h=h, P=?h
h
Pressure distribution 
diagram/pressure profile

 As you know atmospheric pressure reduces, as we move to 
higher elevations.  Is it because of h, as h reduces, P also reduces.
PASCAL’S LAW
5

 “Pressure at any point in fluid is same in all directions when 
the fluid is at rest”

 Consider a wedge shape element of fluid 
having dimension dx, dy and dz along x, y 
and z axis.

 dl= dimension of inclined plane making 
an angle a with the vertical

 Px, Py, Pz and P are pressure acting in x, y, 
z and perpendicular to inclined surface

 dW=weight of element
z
y
x
Py(dxdz)
Px(dydz)
P(dldz)
dx
dy
dz
a
a
a
P(dldz)
cosa
P(dldz)
sina
dW
z
y
x
PASCAL’S LAW
6
Py(dxdz)
Px(dydz)
P(dldz)
a
a
P(dldz)
cosa
P(dldz)
sina
P P
o dy dz P dydz P
dl dy o dl dy dldz P dydz P
o dldz P dydz P
F
x
x
x
x
x
=
= -
= = -
= -
=
?
) (
/ cos / ) (
cos ) (
0
a
a
Q
dW
P P
o dx dz P dxdz P
dw dl dx o dl dx dldz P dxdz P
o dldz P dW dxdz P
F
y
y
y
y
y
=
= -
? = = -
= - -
=
?
) (
0 & / sin / ) (
sin ) (
0
a
a
Q