A substance capable of flowing – Gases or liquids
A fluid is a substance that continually deforms (flows) under an applied shear stress, or external force
Eg: Milk, water, blood etc.,
Branch of applied mechanics concerned with the statics and dynamics of fluids
The analysis of fluid behaviour is based on fundamental laws of mechanics – conservation of mass, momentum, energy & laws of thermodynamics
Difference between solids and fluidsIf a fluid is at rest there can be no shearing forces acting and therefore all forces in the fluid must be perpendicular to the planes in which they act
It is defined as the property of fluid which offers resistance to the movement of one layer of the fluid to the another adjacent layer of the fluid. It is also known as dynamic viscosity.
Pressure has very little or no effect on the viscosity of fluids
Effect of Temperature on viscosity of liquid:
viscosity of liquid is due to cohesive force between the molecules of adjacent layers. As the temperature increases cohesive force decreases and hence viscosity decreases
Effect of Temperature on viscosity of gases:
Viscosity of gases is due to molecular activity between adjacent layers. As the temperature increases molecular activity increases and hence viscosity increases.
A fluid which has at least some viscosity is called real fluid. Actually all the fluids existing or present in the environment are called real fluids. for example water.
A fluid which has at least some viscosity is called real fluid. Actually all the fluids existing or present in the environment are called real fluids. for example water.A fluid which has at least some viscosity is called real fluid. Actually all the fluids existing or present in the environment are called real fluids. for example water.
If real fluid does not obeys the Newton’s law of viscosity then it is called Non-Newtonian fluid
Eg: toothpaste, shampoo, paint or blood
If a real fluid obeys the Newton’s law of viscosity (i.e the shear stress is directly proportional to the shear strain) then it is known as the Newtonian fluid.
Eg: water, air, thin motor oil etc
A fluid having the value of shear stress more than the yield value and shear stress is proportional to the shear strain (velocity gradient) is known as ideal plastic fluid.
Eg: sewage sludge, cement,clay etc.,
It is defined as the tensile force acting on the surface of a liquid in contact with a gas or on the surface between two immiscible liquids such that the contact surface behaves like a membrane under tension.
It is defined as the tensile force acting on the surface of a liquid in contact with a gas or on the surface between two immiscible liquids such that the contact surface behaves like a membrane under tension.
It is defined as the tensile force acting on the surface of a liquid in contact with a gas or on the surface between two immiscible liquids such that the contact surface behaves like a membrane under tension.
It is defined as the phenomenon of rise or fall o
2. A substance capable of flowing – Gases
or liquids
A fluid is a substance that continually
deforms (flows) under an applied shear
stress, or external force
Eg: Milk, water, blood etc.,
What is a Fluid
3. Branch of applied mechanics concerned
with the statics and dynamics of fluids
The analysis of fluid behaviour is based
on fundamental laws of mechanics –
conservation of mass, momentum, energy
& laws of thermodynamics
Fluid Mechanics
4. Fluids solids
We deal with continuous
streams of fluid without begin
or end
We only consider individual
element in solids
Loosely spaced molecules Densely spaced molecules
Intermolecular forces are
smaller than for solids
Large intermolecular cohesive
force
Fluid deforms continuously
when acted on by a shearing
stress
Solid will not deform
continuously (flow)
Difference between solids and fluids
6. If a fluid is at rest there can be no shearing
forces acting and therefore all forces in the
fluid must be perpendicular to the planes in
which they act
Fluid in statics
7. Density (ℓ):
It is defined as ratio between mass and unit
volume
ℓ = Mass/ volume =kg/m3
ℓ water = 1000kg/m3
ℓ air = 1.24 kg/m3
Specific Weight(w):
It is the weight per unit volume of the fluid.
W= weight/volume N/m3
8. Specific Volume:
It is the volume per unit mass of the fluid.
Volume/mass = 1/ ℓ = m3 /kg
Specific gravity:
It is the ratio of density of the fluid to the
density of a standard fluid
s = ℓ or w of the given fluid/ ℓ or w of the
standard fluid
9. It is defined as the property of fluid which
offers resistance to the movement of one
layer of the fluid to the another adjacent
layer of the fluid. It is also known as dynamic
viscosity.
Viscosity
10. It is defined as the ratio of dynamic viscosity
of fluid to its mass density
Kinematic viscosity
11. Newton’s law of viscosity
It states that the rate of shear stress of
a viscous fluid is directly proportional
to unit rate of shear strain
12. Pressure has very little or no effect on the viscosity of fluids
Effect of Temperature on viscosity of liquid:
viscosity of liquid is due to cohesive force between the
molecules of adjacent layers. As the temperature increases
cohesive force decreases and hence viscosity decreases
Effect of Temperature on viscosity of gases:
Viscosity of gases is due to molecular activity between
adjacent layers. As the temperature increases molecular activity
increases and hence viscosity increases.
Effect of pressure on viscosity
13.
14.
15. A fluid, which is incompressible and is having
no viscosity, is known as an ideal fluid. Ideal
fluid is an imaginary fluid as all the fluids,
which exist, have some viscosity
Ideal fluid
16. Real fluid:
A fluid which has at least some viscosity
is called real fluid. Actually all the fluids
existing or present in the environment
are called real fluids. for example
water.
17. If a real fluid obeys the Newton’s law of
viscosity (i.e the shear stress is directly
proportional to the shear strain) then it is
known as the Newtonian fluid.
Eg: water, air, thin motor oil etc
Newtonian fluid
18. If real fluid does not obeys the Newton’s law
of viscosity then it is called Non-Newtonian
fluid
Eg: toothpaste, shampoo, paint or blood
Non Newtonian fluid
19. A fluid having the value of shear stress more than
the yield value and shear stress is proportional to
the shear strain (velocity gradient) is known as
ideal plastic fluid.
Eg: sewage sludge, cement,clay etc.,
Ideal plastic fluid
20. Compressible fluid
Density changes with applied pressure
Incompressible fluid:
Density not changed by external force acting.
Compressible vs incompressible fluid
21. It is defined as the tensile force acting on the surface of a
liquid in contact with a gas or on the surface between two
immiscible liquids such that the contact surface behaves
like a membrane under tension.
Surface tension
22. It is defined as the phenomenon of rise or fall of the liquid
surface in a small tube relative to the adjacent general level of
liquid when the tube is held vertically in the liquid
Capillarity
23. Total Pressure is defined as the force exerted by a static fluid
on a surface either plane or curved when the fluid comes in
contact with the surfaces. This force always acts normal to
the surface.
Centre of pressure is defined as the point of application of
the total pressure on the surface. There are four cases of
submerged surfaces on which the total pressure force and
centre of pressure is to be determined
Vertical plane surface
Horizontal plane surface
Inclined plane surface
Curved surface
