Stress & Elasticity

Elasticity
Elasticity is that property of the object by virtue of which it regain its original configuration after the
removal of the deforming force.
Elastic Limit
Elastic limit is the upper limit of deforming force upto which, if deforming force is removed, the body
regains its original form completely and beyond which if deforming force is increased the body loses
its property of elasticity and get permanently deformed.
Perfectly Elastic Bodies
Those bodies which regain its original configuration immediately and completely after the removal of
deforming force are called perfectly elastic bodies. e.g., quartz and phosphor bronze etc.
Perfectly Plastic Bodies
Those bodies which does not regain its original configuration at all on the removal of deforming
force are called perfectly plastic bodies, e.g., putty, paraffin, wax etc.
Stress
The internal restoring force acting per unit area of a deformed body is called stress.
Stress = Restoring force / Area
Its unit is N/m or Pascal and dimensional formula is [ML T ].
Stress is a tensor quantity.
Stress is of Two Types
(i) Normal Stress If deforming force is applied normal to the area, then the stress is called normal
stress.
If there is an increase in length, then stress is called tensile stress .
If there is a decrease in length, then stress is called compression stress .
(ii) Tangential Stress If deforming force is applied tangentially, then the stress is called tangential
stress.