The property of a material body by virtue of which it regains its original configuration
(i.e. shape and size) when the external deforming force is removed is called elasticity.
The property of the material body by virtue of which it does not regain its original
configuration when the external force is removed is called plasticity
When deforming force is applied on the body then the equal restoring force in opposite direction is developed
inside the body. The restoring forces per unit area of the body is called stress.
The ratio of the change in configuration (i.e. shape, length or volume) to the original configuration
of the body is called strain
According to this law, within the elastic limit, stress is proportional to the strain.
Corresponding to the three types of strain there are three types of modulus of elasticity
ELONGATION OF ROD UNDER IT’S SELF WEIGHT
It is defined as the ratio of the normal stress to the volume strain
It is defined as the ratio of the tangential stress to the shear strain. Let us
consider a cube whose lower face is fixed and a tangential force F acts on
the upper face whose area is A.
When a wire is stretched by a load, it is seen that for small value of load, the extension
produced in the wire is proportional to the load. On removing the load, the wire returns to its
original length. The wire regains its original dimensions only when load applied is less or
equal to a certain limit. This limit is called elastic limit
We know that some material bodies take some time to regain their original configuration
when the deforming force is removed. The delay in regaining the original configuration by the
bodies on the removal of deforming force is called elastic after effect. The elastic after effect is
negligibly small for quartz fiber and phosphor bronze
ELASTIC POTENTIAL ENERGY STORED IN A STRETCHED WIRE OR IN A ROD
OTHERWAY BY S.H.M.
Some of the important applications of the elasticity of the materials are discussed as
When a solid body slides over another solid body, a frictional-force begins to act between them. This
force opposes the relative motion of the bodies. Similarly, when a layer of a liquid slides over another
layer of the same liquid, a frictional-force acts between them which opposes the relative motion
between the layers
When a liquid flows in a tube, the viscous forces oppose the flow of the liquid,
Hence a pressure difference is applied between the ends of the tube which maintains
the flow of the liquid
The property of a liquid by virtue of which an opposing force (internal friction) comes into play
when ever there is a relative motion between the different layers of the liquid is called viscosity.
Consider a flow of a liquid over the horizontal solid surface as shown in fig
The property of a liquid by virtue of which an opposing force (internal friction) comes into play when ever there is
a relative motion between the different layers of the liquid is called viscosity
Knowledge of viscosity of various liquids and gases have been put to use in daily life. Some
applications of its knowledge are discussed as under
EFFECT OF TEMPERATURE ON THE VISCOSITY
In determining the Electronic Charge by Millikan's Experiment