Mechanical Properties of
Fluids
Praveen sir 9989206040
Praveen sir 9989206040
, Class -12 –Physics-Chapter-2- Mechanical Properties of Fluids
Introduction
Fluid, Fluids at rest
Pressure
Pressure due to a liquid column
Atmospheric pressure
Absolute pressure and Gauge pressure
Hydrostatic Paradox
Pascal's law, Applications
Measurement of pressure
Surface tension
Molecular theory of surface tension
Surface tension and Surface energy
Angle of contact
Effect of impurity and temperature on surface tension
Excess pressure across the free surface of a liquid
Explanation of formation of drops and bubbles
Capillary action
Fluids in motion
Critical velocity and Reynolds number
Viscosity
Coefficient of viscosity
Stokes’ Law
Terminal velocity
Equation of continuity
Bernoulli equation, Applications
Fluid : A fluid is a substance that can flow. A fluid has shear modulus 0 and yield
to shear. Under a shear stress and a pressure gradient, a fluid begins to flow.
Liquids, gases and plasmas are collectively called fluids.
Examples : All gases, all liquids, molten glass and lava, honey, etc.
Properties of Fluids:
1. They do not oppose deformation, they get permanently deformed.
2. They have ability to flow.
3. They have ability to take the shape of the container.
Ideal fluid -Characteristics of an ideal fluid.
An ideal fluid is one that has the following properties :
, It is incompressible, i.e., its density has a constantvalue throughout the
fluid.
Its flow is irrotational, i.e., the flow is steady or laminar. In an irrotational
flow, the fluid doesn't rotate like in a whirlpool and the velocity of the
moving fluid at a specific point doesn't change over time. (Many fluids
change from laminar to turbulent flow as the speed of the fluid increases
above some specific value. This can dramatically change the properties of
the fluid.)
Its flow is nonviscous or inviscid, i.e., internal friction or viscosity is zero so
that no energy lost due the motion of the fluid.
Incompressible fluid : An incompressible fluid is one which does not undergo
change in volume for a large range of pressures. Thus, its density has a constant
value throughout the fluid. In most cases, all liquids are incompressible.
Q. How does a fluid differ from a solid?
Solid Fluid
In response to a shear as well as A fluid, on the other hand, can only
normal force, a solid deforms and be subjected to normal compressive
develops a restoring force. stress, called pressure.
Within the elastic limit, both types of A fluid does not have a definite
deformation is reversible. shape, so that under a shear it begins
A solid changes its shape under a to flow.
shear. Real fluids, with non-Zero viscosity,
A normal force causes a change in its display a weak resistance to shear.
length or volume.
If the elastic limit is exceeded, the
solid gets an irreversible deformation
called a permanent set.
, Plasma : Plasma is a phase of matter which exists at very high temperatures, at
which molecules may disassociate into atoms and ions, and further into electrons
and protons. Plasma, however, has very different properties from the three other
common phases of matter (viz., solid, liquid and gas) due to the strong electrical
forces between the charges.
The term fluid includes both the liquid and gas phases.
It is commonly used, as a synonym for liquid only, without any reference to gas.
For example, ’brake fluid’ is hydraulic oil and will not perform its required function
if there is gas in it! This colloquial use of the term is also common in the fields of
medicine and nutrition, e.g. ”take plenty of fluids.”
Pressure
Pressure : The pressure at a point in a fluid in hydrostatic equilibrium is defined as
the normal force per unit area exerted by the fluid on a surface of infinitesimal area
containing the point.
𝐹
Thus, the pressure, 𝑝 = lim
∆𝐴→0 ∆𝐴
where F is the magnitude of the normal force on a surface of area A. The pressure
is defined to be a scalar quantity.
SI unit = the pascal (Pa), 1 Pa = 1 N-m-2
CGS unit : the dyne per square centimeter (dyn/cm2)
Dimensions = [p] = [F][A-1] = [MLT-2 , L-2 ] = [ML-1T-2]
Two non-SI units of pressure, which are either of historical interest, or are still
used in specific fields are the bar and the torr.
1 bar = 0.1 MPa = 100 kPa = 1000 hPa =105Pa
1 torr = (101325/ 760) Pa = 133.32 Pa
[Note : Their use in modern scientific and technical work is strongly discouraged]
Fluids
Praveen sir 9989206040
Praveen sir 9989206040
, Class -12 –Physics-Chapter-2- Mechanical Properties of Fluids
Introduction
Fluid, Fluids at rest
Pressure
Pressure due to a liquid column
Atmospheric pressure
Absolute pressure and Gauge pressure
Hydrostatic Paradox
Pascal's law, Applications
Measurement of pressure
Surface tension
Molecular theory of surface tension
Surface tension and Surface energy
Angle of contact
Effect of impurity and temperature on surface tension
Excess pressure across the free surface of a liquid
Explanation of formation of drops and bubbles
Capillary action
Fluids in motion
Critical velocity and Reynolds number
Viscosity
Coefficient of viscosity
Stokes’ Law
Terminal velocity
Equation of continuity
Bernoulli equation, Applications
Fluid : A fluid is a substance that can flow. A fluid has shear modulus 0 and yield
to shear. Under a shear stress and a pressure gradient, a fluid begins to flow.
Liquids, gases and plasmas are collectively called fluids.
Examples : All gases, all liquids, molten glass and lava, honey, etc.
Properties of Fluids:
1. They do not oppose deformation, they get permanently deformed.
2. They have ability to flow.
3. They have ability to take the shape of the container.
Ideal fluid -Characteristics of an ideal fluid.
An ideal fluid is one that has the following properties :
, It is incompressible, i.e., its density has a constantvalue throughout the
fluid.
Its flow is irrotational, i.e., the flow is steady or laminar. In an irrotational
flow, the fluid doesn't rotate like in a whirlpool and the velocity of the
moving fluid at a specific point doesn't change over time. (Many fluids
change from laminar to turbulent flow as the speed of the fluid increases
above some specific value. This can dramatically change the properties of
the fluid.)
Its flow is nonviscous or inviscid, i.e., internal friction or viscosity is zero so
that no energy lost due the motion of the fluid.
Incompressible fluid : An incompressible fluid is one which does not undergo
change in volume for a large range of pressures. Thus, its density has a constant
value throughout the fluid. In most cases, all liquids are incompressible.
Q. How does a fluid differ from a solid?
Solid Fluid
In response to a shear as well as A fluid, on the other hand, can only
normal force, a solid deforms and be subjected to normal compressive
develops a restoring force. stress, called pressure.
Within the elastic limit, both types of A fluid does not have a definite
deformation is reversible. shape, so that under a shear it begins
A solid changes its shape under a to flow.
shear. Real fluids, with non-Zero viscosity,
A normal force causes a change in its display a weak resistance to shear.
length or volume.
If the elastic limit is exceeded, the
solid gets an irreversible deformation
called a permanent set.
, Plasma : Plasma is a phase of matter which exists at very high temperatures, at
which molecules may disassociate into atoms and ions, and further into electrons
and protons. Plasma, however, has very different properties from the three other
common phases of matter (viz., solid, liquid and gas) due to the strong electrical
forces between the charges.
The term fluid includes both the liquid and gas phases.
It is commonly used, as a synonym for liquid only, without any reference to gas.
For example, ’brake fluid’ is hydraulic oil and will not perform its required function
if there is gas in it! This colloquial use of the term is also common in the fields of
medicine and nutrition, e.g. ”take plenty of fluids.”
Pressure
Pressure : The pressure at a point in a fluid in hydrostatic equilibrium is defined as
the normal force per unit area exerted by the fluid on a surface of infinitesimal area
containing the point.
𝐹
Thus, the pressure, 𝑝 = lim
∆𝐴→0 ∆𝐴
where F is the magnitude of the normal force on a surface of area A. The pressure
is defined to be a scalar quantity.
SI unit = the pascal (Pa), 1 Pa = 1 N-m-2
CGS unit : the dyne per square centimeter (dyn/cm2)
Dimensions = [p] = [F][A-1] = [MLT-2 , L-2 ] = [ML-1T-2]
Two non-SI units of pressure, which are either of historical interest, or are still
used in specific fields are the bar and the torr.
1 bar = 0.1 MPa = 100 kPa = 1000 hPa =105Pa
1 torr = (101325/ 760) Pa = 133.32 Pa
[Note : Their use in modern scientific and technical work is strongly discouraged]
