Deforming Force
A force which produces a change in configuration of the object on applying it , is called a deforming force .
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 2 or Pascal and dimensional formula is [ ML -12 T -2 ]. 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 .