CHAPTER – 9
Mechanical Properties of
Fluids
Topics to be covered
1. pressure
2. pascal’s Law
3. Hydraulic Machines
4. Streamline flow
5. Equation of Continuity
6. Bernoulli’s principle
7. Speed of Efflux (Torricell’s Law)
8. Dynamic Lift (Magnus Effect + Aerofoil)
9. Viscosity
10. Stokes’ Law
11. Terminal Velocity
12. Surface Tension
13. Molecular theory of Surface Tension
14. Angle of Contact & Wetting
15. Drops, Bubble, Excess Pressure
16. Capillarity
, ➢ What is Fluids?
A fluid is a substance that can flow and does not
have a fixed shape of its own.
Liquid and gases are called fluid because they
easily deform under very small shear stress and
take the shape of the container in which they are
kept.
❖ Type of fluids
• Hydrostatics: Branch of physics that deals
with the study of fluids at rest.
,• Hydrodyanamics: Branch of physics that
deals with the study of fluids in motion.
• Viscosity/Surface Tension
➢ PRESSURE
Pressure is defined as the normal force acting
per unit area.
P=F/A
• Pressure is a scalar quantity.
• Only the normal component of force is used in
formula, not the full vector force.
• Dimensions: [ML-1 T-2]
• SI unit: Pascal (Pa) = 1N/m2
• A commonly used unit is the atmosphere(atm):
1atm = 1.013 x 105 Pa
Average Pressure
If F is the magnitude of the normal force on a
piston of area A, then average pressure is defined
as the normal force per unit area.
, Pav = F/A
Pressure in the Limiting Sense:
• The piston area can be made arbitrarily small.
• Pressure is then defined as the limit.
P =lim A →0 𝜟F/𝜟A
➢ Pressure Exerted by Fluids at Rest
• When an object is submerged in a fluid at rest,
the fluid exerts a force on every part of its
surface. This force is always normal
(perpendicular) to the surface of the object.
• If any part of this force had a parallel
component, the object would exert an equal
and opposite parallel force on the fluid,
according to newtons third law. such a force
would cause the fluid to flow parallel to the
surface of the object. But the fluid is at rest, so
no parallel flow is possible.
Mechanical Properties of
Fluids
Topics to be covered
1. pressure
2. pascal’s Law
3. Hydraulic Machines
4. Streamline flow
5. Equation of Continuity
6. Bernoulli’s principle
7. Speed of Efflux (Torricell’s Law)
8. Dynamic Lift (Magnus Effect + Aerofoil)
9. Viscosity
10. Stokes’ Law
11. Terminal Velocity
12. Surface Tension
13. Molecular theory of Surface Tension
14. Angle of Contact & Wetting
15. Drops, Bubble, Excess Pressure
16. Capillarity
, ➢ What is Fluids?
A fluid is a substance that can flow and does not
have a fixed shape of its own.
Liquid and gases are called fluid because they
easily deform under very small shear stress and
take the shape of the container in which they are
kept.
❖ Type of fluids
• Hydrostatics: Branch of physics that deals
with the study of fluids at rest.
,• Hydrodyanamics: Branch of physics that
deals with the study of fluids in motion.
• Viscosity/Surface Tension
➢ PRESSURE
Pressure is defined as the normal force acting
per unit area.
P=F/A
• Pressure is a scalar quantity.
• Only the normal component of force is used in
formula, not the full vector force.
• Dimensions: [ML-1 T-2]
• SI unit: Pascal (Pa) = 1N/m2
• A commonly used unit is the atmosphere(atm):
1atm = 1.013 x 105 Pa
Average Pressure
If F is the magnitude of the normal force on a
piston of area A, then average pressure is defined
as the normal force per unit area.
, Pav = F/A
Pressure in the Limiting Sense:
• The piston area can be made arbitrarily small.
• Pressure is then defined as the limit.
P =lim A →0 𝜟F/𝜟A
➢ Pressure Exerted by Fluids at Rest
• When an object is submerged in a fluid at rest,
the fluid exerts a force on every part of its
surface. This force is always normal
(perpendicular) to the surface of the object.
• If any part of this force had a parallel
component, the object would exert an equal
and opposite parallel force on the fluid,
according to newtons third law. such a force
would cause the fluid to flow parallel to the
surface of the object. But the fluid is at rest, so
no parallel flow is possible.
