This doucment has in depth information on the topic elasticity which is one of the important lesson of physics. It gives the simple explanation about elasticiy, plastocity, stress, strain, hookes law , modulus of elasticity and many more. This document also include solved question and answer as w...
, . Tangential Stress
Elasticity If the deforming force is tangential to the surface of
Elasticity is a fundamental property of all matter by an object, the stress is called tangential stress. This
virtue of which an object regains its original shape is seen when an object is twisted.
and size when a deforming force is removed. When
the deforming force is applied to this object, it Strain
displaces the molecules of the object from their The change in size or shape of an object due to the
original states. Consequently, a force of reaction deforming force is called strain and is measured as
called restoring force is produced. This is due to the the ratio of change in size of the object to the
intermolecular forces with which the object tends to original size.
regain its original state.
By the deforming force we mean that it is an Longitudinal Strain
external force being applied to an object to make it It is defined as the change in length per unit original
deform. length. It is also known as tensile strain. That is,
change in length L l
longitudinal strain
Difference between Elasticity and Plasticity
(1) Elasticity is the (1) Plasticity is the original length L L
property of an object property of an object
by virtue of which it by virtue of which it Volume Strain
can regain its original can't regain its original It is defined as change in volume per unit original
shape and size when shape and size when volume. That is,
the deforming force is the deforming force is change in volume V
removed. removed. volumetric strain
original volume V
(2) For the same amount (2) For the same amount
of a deforming force, of a deforming force, Shear Strain
less extension is more extension is
It is defined as the angle through which a line
produced in it. produced in it.
originally perpendicular to a fixed face is turned.
(3) Elastic object follows (3) Plastic object doesn't
The angle is called the angle of shear.
Hooke's law within follow Hooke's law.
elastic limit.
Hooke's Law
Original Hooke's Law
Stress Within elastic limit, the force F applied to stretch an
The internal restoring or elastic force acting per unit elastic wire is directly proportional to the extension
area of a deformed object is called stress. Since in x in the wire. That is,
equilibrium, the internal restoring force is equal to Fx
the deforming force in magnitude, stress is or F = kx
measured as the deforming force per unit area of the where k is proportionality constant called force
object. That is, constant whose value depends on the nature of the
deforming force F wire. It is measured in newtons per meter (N/m).
stress
area A
F Modified Hooke's Law
or stress Young modified the original form of Hooke's law
A which states that within elastic limit, stress is
There are two types of stress. directly proportional to strain. That is,
stress strain
Normal stress or stress constant strain
If the deforming force is applied normally to the stress
surface of an object, the stress is called normal or constant E
stress. The stretching of a rod or a wire by pulling strain
its ends produces the tension in it. So the normal where E is called the modulus of elasticity. There
stress is also called tensile stress. are different types of modulus of elasticity.
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