The atoms in solids are held together by interatomic forces. The average locations of the atoms in a lattice do not change with time. Since the atoms are almost lacking in mobility, their kinetic energy is negligibly small. It is this lack of mobility which makes a solid rigid. This rigidity is the cause of elasticity in solids. In some solids such as steel, the atoms are bound together by larger interatomic forces than in solids such as aluminium. Thus, the elastic behaviour varies from solid to solid. Even fluids exhibit elasticity. All material bodies get deformed when subjected to a suitable force. The ability of a body to regain its original shape and size is called elasticity. The deformating force per unit area is called stress. The change in the dimensions (length, shape or volume) divided by the original dimension is called strain. The three kinds of stresses are tensile stress, shearing stress and volumetric stress. The corresponding strainsare called tensile strain, shearing strain and volume strain. According to Hookes' law, within the elastic limit stress is proportional to strain. The ratio stress/strain is called the modulus of elasticity. Figure shows the strain-stress graphs for materials A and B. From the graph it follows that

The atoms in solids are held together by interatomic forces. The average locations of the atoms in a lattice do not change with time. Since the atoms are almost lacking in mobility, their kinetic energy is negligibly small. It is this lack of mobility which makes a solid rigid. This rigidity is the cause of elasticity in solids. In some solids such as steel, the atoms are bound together by larger interatomic forces than in solids such as aluminium. Thus, the elastic behaviour varies from solid to solid. Even fluids exhibit elasticity. All material bodies get deformed when subjected to a suitable force. The ability of a body to regain its original shape and size is called elasticity. The deformating force per unit area is called stress. The change in the dimensions (length, shape or volume) divided by the original dimension is called strain. The three kinds of stresses are tensile stress, shearing stress and volumetric stress. The corresponding strainsare called tensile strain, shearing strain and volume strain. According to Hookes' law, within the elastic limit stress is proportional to strain. The ratio stress/strain is called the modulus of elasticity. Fig. is the load extension curve fora metalic wire. Over which region is Hookes law obeyed?

The atoms in solids are held together by interatomic forces. The average locations of the atoms in a lattice do not change with time. Since the atoms are almost lacking in mobility, their kinetic energy is negligibly small. It is this lack of mobility which makes a solid rigid. This rigidity is the cause of elasticity in solids. In some solids such as steel, the atoms are bound together by larger interatomic forces than in solids such as aluminium. Thus, the elastic behaviour varies from solid to solid. Even fluids exhibit elasticity. All material bodies get deformed when subjected to a suitable force. The ability of a body to regain its original shape and size is called elasticity. The deformating force per unit area is called stress. The change in the dimensions (length, shape or volume) divided by the original dimension is called strain. The three kinds of stresses are tensile stress, shearing stress and volumetric stress. The corresponding strainsare called tensile strain, shearing strain and volume strain. According to Hookes' law, within the elastic limit stress is proportional to strain. The ratio stress/strain is called the modulus of elasticity. The metal shows plastic behaviour beyond point