<P> Physical properties of elements and compounds which provide conclusive evidence of chemical composition include odor, color, volume, density (mass per unit volume), melting point, boiling point, heat capacity, physical form and shape at room temperature (solid, liquid or gas; cubic, trigonal crystals, etc .), hardness, porosity, index of refraction and many others . This section discusses some physical properties of materials in the solid state . </P> <P> The mechanical properties of materials describe characteristics such as their strength and resistance to deformation . For example, steel beams are used in construction because of their high strength, meaning that they neither break nor bend significantly under the applied load . </P> <P> Mechanical properties include elasticity and plasticity, tensile strength, compressive strength, shear strength, fracture toughness, ductility (low in brittle materials), and indentation hardness . Solid mechanics is the study of the behavior of solid matter under external actions such as external forces and temperature changes . </P> <P> A solid does not exhibit macroscopic flow, as fluids do . Any degree of departure from its original shape is called deformation . The proportion of deformation to original size is called strain . If the applied stress is sufficiently low, almost all solid materials behave in such a way that the strain is directly proportional to the stress (Hooke's law). The coefficient of the proportion is called the modulus of elasticity or Young's modulus . This region of deformation is known as the linearly elastic region . Three models can describe how a solid responds to an applied stress: </P>

Characteristics and properties of solid liquid and gas