Differentiate between Strength of Materials and Engineering Mechanics

There are three fundamental areas of mechanics of solids are statics, dynamics and strength of materials.

Strength of materials is basically a branch of `Solid Mechanics'. The other important branch of solid mechanics is Engineering Mechanics: statics and dynamics. Whereas `Engineering Mechanics' deals with mechanical behavior of rigid (non-deformable) solids subjected to external loads, the 'Strength of Materials' deals with mechanical behavior of non-rigid (deformable) solids under applied external loads. It is also known by other names such as Mechanics of Solids, Mechanics of Materials, and Mechanics of Deformable Solids. Summarily, the studies of solid mechanics can be grouped as follows. 

Since none of the known materials are rigid, therefore the studies of Engineering Mechanics are based on theoretical aspects; but because all known materials are deformable, the studies of strength of materials are based on realistic concepts and practical footings. The study of Strength of Materials helps the design engineer to select a material of known strength at minimum expenditure. 

Studies of Strength of Materials are applicable to almost all types of machine and structural components, all varieties of materials and all shapes and cross-sections of components. There are numerous variety of components, each behaving differently under different loading conditions. These components may be made of high strength steel, low strength plastic, ductile aluminum, brittle cast iron, flexible copper strip, or stiff tungsten.