TECHNICAL TERMS OF STRENGTH OF MATERIALS

Strain: 
When a single force or a system force acts on a body, it undergoes some deformation. This deformation per unit length is known as strain. Mathematically strain may be defined as deformation per unit length. 
So, 
Strain=Elongation/Original length 

Elasticity; 
The property of material by virtue of which it returns to its original shape and size upon removal of load is known as elasticity. 

Hooks Law 
It states that within elastic limit stress is proportional tostrain. Mathematically 
E=Stress/Strain
Where E = Young’s Modulus 
Hooks law holds good equally for tension and compression. 

Poisson’s Ratio; 
The ratio lateral strain to longitudinal strain produced by a single stress is known as Poisson’s ratio. 

Modulus of Elasticity (or Young’s Modulus) 
Young’s modulus is defined as the ratio of stress to strain within elastic limit.