Mechanical properties of fluid class 11-PCM

K.V. Lumding; K.V. Karimganj; K.V. Langjing


MECHANICS OF SOLID AND FLUID
 Deforming force:- A force acting on a body which produces change in its
shape of body instead of its state of rest or uniform motion of the body.
 Elasticity:-The property of matter by virtue which it regains its original shape
and size, when the deforming forces are removed is called elasticity.
 Plasticity:- The inability of a body to return to its original shape and size,
when the deforming forces are removed is called plasticity.
 Hooke’s law:- when a wire is loaded within elastic limit, the extension
produced in wire is directly proportional to the load applied.
OR
Within elastic limit stress α strain
Stress = Constant
Strain
 Stress :- Restoring force set up per unit area when deforming force acts on
the body
Stress = Restoring force
Area
S.I Unit of stress = N/m2 or Pascal (Pa)
Dimensional formula = Ma LbTc


Tensile stress(When there is an
Types of stress:- increase in dimension of the body
along the direction of force )
Normal stress

Stress Compression stress(when there is
decrease in dimension )

Tangential stress (When deforming force acts tangential to the
surface of body )




Strain:- The ratio of change in dimension to the original dimension is called strain

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,K.V. Lumding; K.V. Karimganj; K.V. Langjing


It has no unit
Longitudinal strain=
Types of strain:-


Volumetric strain =


Sharing Strain = φ = , Where =displacement of the face
on which force is applied and L is the height of the face



Hooke’s L aw:- Within elastic limit, stress α strain

= Constant (Modulus of Elasticity)

Modulus of elasticity are of 3 types.

(1) Young’s Modulus (Y) =


(2) Bulk Modulus (K) =


(3) Modulus of rigidity modulus (ƞ) =

 Compressibility : the reciprocal of bulk modulus of a material is called its
compressibility
Compressibility = 1/K
Stress – Strain- diagram
 Proportionality limit(P) – The stress at the limit of proportionality point P is
known as proportionality limit
 Elastic limit - the maximum stress which can be applied to a wire so that on
unloading it return to its original length is called the elastic limit
 Yield point(Y)- The stress, beyond which the length of the wire increase
virtually for no increase in the stress
 Plastic region- the region of stress- strain graph between the elastic limit and
the breaking point is called the plastic region.


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, K.V. Lumding; K.V. Karimganj; K.V. Langjing


 Fracture point or Breaking point(B)- the value of stress corresponding to
which the wire breaks is called breaking point
 Work done in stretching a wire per unit volume/energy sored per unit
volume of specimen
= ½ x stress x strain
 Elastic after effect:- The delay in regaining the original state by a body after
the removal of the deforming force is called elastic after effect.
 Elastic fatigue:- the loss in strength of a material caused due to repeated
alternating strains to which the material is subjected.
 Poisson’s ratio(ϭ) :- The ratio of lateral strain to longitudinal strain is called

Poisons ratio =

 Relation between Y,K,¶, ϭ
1. Y=3K(1-2 ϭ)
2. Y=2¶(1+ ϭ)
¶
3. ϭ = ¶+

4. = 1/K +3/¶

 Applications of elasticity
1. Metallic part of machinery is never subjected to a stress beyond the elastic
limit of material.
2. Metallic rope used in cranes to lift heavy weight are decided on the elastic
limit of material
3. In designing beam to support load (in construction of roofs and bridges)
4. Preference of hollow shaft than solid shaft
5. Calculating the maximum height of a mountain


MECHANICS OF FLUID

 Pressure :The force/threat acting per unit area is called pressure
S.I Unit of pressure is N/M2 or pascal (Pa)


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