Ch 9 covers the mechanical properties of solids — elasticity, stress-strain relationships, Hooke's law, moduli of elasticity, and the stress-strain curve for ductile and brittle materials.
Stress: restoring force per unit area (Pa). Types: tensile (stretching), compressive, shear (tangential). Strain: fractional deformation (dimensionless). Types: longitudinal (ΔL/L), volumetric (ΔV/V), shear (tanφ). Hooke's law: within elastic limit, stress ∝ strain. Modulus of elasticity = stress/strain.
Young's modulus Y = tensile stress/longitudinal strain = (F/A)/(ΔL/L). Bulk modulus B = −V(ΔP/ΔV) (resistance to volume change). Shear modulus G = shear stress/shear strain. Poisson's ratio: lateral strain/longitudinal strain. Stress-strain curve: proportional limit → elastic limit → yield point → plastic region → fracture.
Download: https://ncert.nic.in/textbook/pdf/keph201.pdf | Part II: https://ncert.nic.in/textbook/pdf/keph2ps.zip
Elastic deformation: the body returns to its original shape when the force is removed (within Hooke's law region). Plastic deformation: the body permanently changes shape even after the force is removed (beyond the elastic limit). Ductile materials (copper, gold) show large plastic deformation before breaking; brittle materials (glass, cast iron) break suddenly with little plastic deformation.
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