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.