1. MET 306
Fluid Mechanics
Lecture # 2
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2. Objective
 Determine the pressure at various locations in a fluid at rest.
 Explain the concept of manometers and apply appropriate
equations to determine pressures.
 Calculate the hydrostatic pressure force on a plane or curved
submerged surface.
 Calculate the buoyant force and discuss the stability of floating
or submerged objects.
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3. Pressure at Point
Fluid Pressure
Pressure is used to indicate the normal force per unit area (P=F/A) at a
given point acting on a given plane within the fluid mass of interest.
Py Ps Pz Ps
Py Ps Pz
That conclude the pressure at a point in a fluid at rest is independent of direction as long as there
are no shearing stresses present. This important result is known as Pascal’s law
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4. Basic Equation For Pressure Filed
dp
dz
This equation indicate that the pressure gradient in vertical direction is negative
that is the pressure decrease as we move upward in the fluid at reset
Incompressible Fluid
 ( ρ ) constant
 ( g )in most of fluid application is neglected
Compressible flow P1 h p2
( ρ ) is not constant
 p R T
g ( z2 z1 )
P2 p1 exp
RT 0
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5. Basic Equation For Pressure Filed
Open
Example
A tank has a gasoline and water as shown in the
Figure. If the SG of gasoline is 0.68 determine the
pressure at the gasoline water interface and at the 17 ft
bottom of the tank Gasoline
Water 3 ft
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6. Pressure Variation in Fluid at Rest
p=po
h
A B
γ = specific weight
The pressure is the same at tall points along the line AB even with
irregular shape
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7. Pressure Measurement
Representation of gage and absolute pressure
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8. Pressure Measurement
Manometer
Manometer has three types:
Piezometer Tube
U-Tube Manometer
Inclined-Tube Manometer
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9. Piezometer Tube
PA h
1 1
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10. U-Tube Manometer
pA 2
h2 1
h1
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11. U-Tube Manometer
Example
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12. Inclined-Tube Manometer
Example
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