class 11 || Physics chapter-09 || Mechanical Properties of Solids..|| handmade NCERT complete notes💯

Mechanical Properties of Solids A material is said to be in the solid state if all the atoms of that matter are densely packed together. A solid material has a definite shape and size. In order to change the shape and size of the solid object, an external force needs to be applied. In this chapter, we will learn about the Mechanical Properties of Solids. Elasticity and Plasticity By now, you probably know about the concept of elasticity. In layman terms, it means that some substances get back to their original shape after being stretched. You have played with a slingshot. Haven’t you? That is an elastic material. Let us get into the concepts of elasticity and plasticity and learn more about these two properties of matter. Elasticity is the property of a body to recover its original configuration (shape and size) when you remove the deforming forces. Plastic bodies do not show a tendency to recover to their original configuration when you remove the deforming forces. Plasticity is the property of a body to lose its property of elasticity and acquire a permanent deformation on the removal of deforming force. Stress The restoring force (F) per unit area (A) is called stress. The unit of stress in S.I system is N/m2 and in C.G.S-dyne/cm2. The dimension of stress = [M1L-1T-2]. Stress is given by, Stress = F/A Types of Stress Stress could be of the following types: Normal stress:- Normal stress has the restoring force acting at right angles to the surface. Compressional stress:- This stress produces a decrease in length per volume of the body. Tensile stress:- This stress results in an increase in length per volume of the body. Tangential stress:- Stress is said to be tangential if it acts in a direction parallel to the surface. Strain The strain is the relative change in configuration due to the application of deforming forces. It has no unit or dimensions. The strain could be of the following types: Longitudinal Strain: It is the ratio between the change in length (l) to its original length (L). Longitudinal strain = l/L Lateral Strain: The lateral strain is the ratio between the change in diameter to its original diameter when the cylinder is subjected to a force along its axis. Lateral strain = change in diameter /original diameter Volumetric Strain: It is the ratio between the change in volume (v) to its original volume (V). Volume strain = v/V. unit stress. σ = lateral strain/longitudinal strain = β/α = (ΔD/D)/(ΔL/L). Values of σ lie between -1 and 0.5. Relations Among Elastic Constants B= Y/[3(1-2σ)] η = Y/[2(1+ σ)] 9/Y = 3/η + 1/B σ = [3B-2η]/[6B+2η]