Engineering Physics

1. Physics Department Diploma Engineering
Engineering Physics

2. Physics Department Diploma Engineering
Physics Department Diploma Engineering
Chapter-3
General Properties of Matter
Part-I

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Table of Content
• Part-I ELASTICITY
• Part-II Surface Tension
• Part-III Viscosity
• Part-I ELASTICITY
• Elasticity , Plasticity , Elastic Limit
• Deforming Force & Restoring Force
• Stress & Its Unit
• Types of Stress
• Types of Strain
• Young Modulus
• Bulk Modulus
• Modulus of Rigidity
• Stress - Strain Diagram

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Elasticity , Plasticity , Elastic Limit
• The opposite of elasticity is plasticity;
when something is stretched, and it
stays stretched, the material is said to
be plastic.
• When energy goes into changing the
shape of some material and it stays
changed, that is said to be plastic
deformation.
• The elastic limit is the stress value
beyond which the material no longer
behaves elastically but becomes
permanently deformed.

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Deforming Force & Restoring Force
• Deforming Force:
• The external force acting on a body on
account of which its size or shape or
both change is defined as
the deforming force.
• Restoring Force:
• The force which restores the size and
shape of the body when
deformation forces are removed is
called restoring force.

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Stress & Unit
• In continuum mechanics, stress is a
physical quantity that expresses the
internal forces that neighboring
particles of a continuous material
exert on each other, while strain is the
measure of the deformation of the
material.
• SI Units: N/m2
• Symbols: σ

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Types of Stress

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Strain & Its Unit
• Strain =
𝐶ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑙𝑒𝑛𝑔𝑡ℎ
𝑂𝑟𝑖𝑔𝑛𝑎𝑙 𝐿𝑒𝑛𝑔𝑡ℎ
• Unitless Quantity

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Types of Strain

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Young Modulus, Bulk Modulus, Modulus of Rigidity

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Stress - Strain Diagram

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Table of Content
• Part-I Elasticity
• Part-II Surface Tension
• Part-III Viscosity
• Part-II Surface Tension
• Define Surface Tension
• Application of Surface Tension
• Cohesive force & Adhesive force
• Angel of Contact
• Effect of Temperature
• Laplace's Molecular Theory
• Capillarity (Capillary Action)

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Definition Surface Tension
• Surface tension is the tension of the
surface film of a liquid caused by the
attraction of the particles in the
surface layer by the bulk of the liquid,
which tends to minimize surface area.
• Surface tension = F/L
• SI Unit = N/m
• CGS Unit = dyne/cm

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Application of Surface Tension-1
• Insects Walking on Water
• Floating a Needle on the surface of
the water.
• Rainproof tent materials where the
surface tension of water will bridge
the pores in the tent material
• Clinical test for jaundice
• Surface tension the disinfectants
(disinfectants are solutions of low
surface tension).

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Application of Surface Tension-2
• Cleaning of clothes by soaps and
detergents which lowers the surface
tension of the water
• Washing with cold water
• Round bubbles where the surface
tension of water provides the wall
tension for the formation of water
bubbles.
• This phenomenon is also responsible
for the shape of liquid droplets.

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Cohesive Force & Adhesive Force
• When two similar substances or
molecules face force of attraction this
force is known as cohesion force.
• Adhesion happens between two
dissimilar molecules or substances.
• The force of cohesion is defined as
the force of attraction between
molecules of the same substance.
• The force of adhesion is defined as
the force of attraction between
different substances, such as glass
and water.

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Angel of Contact
• The angle subtended by the tangent
on the surface of a liquid drop on a
solid surface from the point
of contact is called the angle of
contact.
• When the solid attracts the liquid
molecules, the angle becomes obtuse,
and when repulsion is there,
the angle becomes acute.

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Effect of Temperature on Surface Tension
• Surface tension decreases
when temperature increases
• Because cohesive forces decrease with
an increase of molecular thermal
activity.
• In general, surface tension decreases
when temperature increases because
cohesive forces decrease with an
increase of molecular thermal activity.
• The influence of the surrounding
environment is due to the adhesive
action of liquid molecules that they
have at the interface.

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Capillarity & Capillary Action
• The tendency of a liquid in a capillary
tube or absorbent material to rise or
fall as a result of surface tension.
• Capillary action is the ability of a
liquid to flow in narrow spaces
without the assistance of, or even in
opposition to, external forces like
gravity.
• Capillary penetration in porous media
shares its dynamic mechanism with
flow in hollow tubes, as both processes
are resisted by viscous forces.

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Applications of Capillarity
• The oil rises through wicks of lamp
through capillary action.
• Any liquid will be absorbed by the
sponges through capillary action.
• Ink will be absorbed by blotting paper.
• Lubricating oil spread easily on all
parts because of their low surface
tension.
• Cotton dresses are preferred in
summer because cotton dresses have
fine pores which act as capillaries for
sweat.

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Table of Content
• Part-I Elasticity
• Part-II Surface Tension
• Part-III Viscosity
Part-III Viscosity
• Viscosity
• Newton’s Law of Viscosity
• Coefficient of Viscosity
• Reynolds's Number
• Stream Line & Turbulent Flow
• Stroke's Law
• Terminal Velocity

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Viscosity
• The viscosity of a fluid is a measure of
its resistance to deformation at a
given rate. Viscosity denotes
opposition to flow.
• For Liquids, it corresponds to the
informal concept of ‘thickness’.
• For Example, syrup has a higher
viscosity than water.

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Viscosity
• The viscosity of liquids decreases
rapidly with an increase in
temperature, and the viscosity of
gases increases with an increase in
temperature.
• Thus, upon heating, liquids flow more
easily, whereas gases flow more
sluggishly.

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Newton’s Law of Viscosity
• Newton’s viscosity law’s states that,
the shear stress between adjacent
fluid layers is proportional to the
velocity gradients between the two
layers.
• The ratio of shear stress to shear rate
is a constant, for a given temperature
and pressure, and is defined as the
viscosity or coefficient of viscosity.
Where,
𝜇 = Coefficient of Viscosity
𝜏 = Share Stress = F/A
𝑑𝑢
𝑑𝑦
= Rate of Shear Deformation
𝜏 ∝
𝑑𝑢
𝑑𝑦
𝜏 = 𝜇
𝑑𝑢
𝑑𝑦

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Coefficient of Viscosity
• The viscosity is calculated in terms of
the coefficient of viscosity.
• It is constant for a liquid and depends
on it’s liquid’s nature. The Poiseuille’s
method is formally used to estimate
the coefficient of viscosity, in which
the liquid flows through a tube at the
different level of pressures.

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Coefficient of Viscosity
• The coefficient of viscosity of fluids
will be decreased as the temperature
increases, while it is inverse in the
case of gases.
• While the coefficient of viscosity of
gases will increase with the increase
in temperature.
• The increase in temperature for the
fluid deliberate the bonds between
molecules.
• These bonds are directly associated
with the viscosity and finally, the
coefficient is decreased.

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Reynold's Number
• The Reynold’s Number (Re) is an
important dimensionless quantity in
fluid mechanics used to help predict
flow patterns in different fluid flow
situations.
• At Low Reynolds numbers, flows tend
to be dominated by Laminar Flow
• At High Reynolds numbers turbulence
results from differences in the fluid's
speed and direction, which may
sometimes intersect or even move
counter to the overall direction of the
flow.

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Stream Line & Turbulent Flow
• Streamline flow in fluids is defined as
the flow in which the fluids flow in
parallel layers such that there is no
disruption or intermixing of the layers
and at a given point, the velocity of
each fluid particle passing by remains
constant with time.
• At low fluid velocities, there are no
turbulent velocity fluctuations and
the fluid tends to flow without lateral
mixing.

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Stream Line & Turbulent Flow
• The motion of particles of the fluid
follows a particular order with respect
to the particles moving in a straight
line parallel to the wall of the pipe
such that the adjacent layers slide
past each other like playing cards.
• Streamlines are defined as the path
taken by particles of a fluid under
steady flow conditions. If we represent
the flow lines as curves, then the
tangent at any point on the curve
gives the direction of fluid velocity at
that point.

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Stroke's Law
• The force of viscosity on a small
sphere moving through a viscous fluid
is given by
𝐹𝑑 = 6𝜋η𝑟𝜈
• Where
• Fd = Frictional Force
• η = Dynamic Viscosity
• r = Radius of the Spherical Object
• v = Flow Velocity relative to the
object.

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Terminal Velocity
• Terminal velocity is the maximum
velocity attainable by an object as it
falls through a fluid (air is the most
common example).
• It occurs when the sum of the drag
force (Fd) and the buoyancy is equal to
the downward force of gravity (FG)
acting on the object.
• Since the net force on the object is
zero, the object has zero acceleration

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Physics Department Diploma Engineering
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