# Mechanical Properties Of Solids Class 11 Notes Physics Chapter 9 - CBSE

## Chapter : 9

## What Are Mechanical Properties Of Solids ?

The dot mark ◉ field are mandatory, So please fill them in carefully

**To download the complete Syllabus (PDF File), Please fill & submit the form below.**
https://drive.google.com/file/d/11OVmfDC66nqufTR2A2gyeYC7ZU9v2_HP/view

- Elasticity is the property of a solid by virtue of which it regains its original shape or size after the externally applied deforming force has been removed.
- Restoring force per unit area is called stress.
- Magnitude of the stress =

$$\frac{\text{F}}{\text{A}}$$

- The SI unit of stress in Nm
^{–2}. - When a deforming force acts normally over a surface of a body, then the internal restoring force set up per unit area of the body is called normal stress.
- Strain is the deformation per unit of the relevant dimensions of the substance.
- Hooke's law states that, within proportionality limit, stress ∝ strains or stress = k × strains

The proportionality constant k is called the modulus of elasticity. It is denoted as:

- Young's modulus (Y) in case of longitudinal stress.
- Shear Modulus or Modulus of Rigidity (n) in case of tangential stress.
- Bulk Modulus (K) in case of volumetric stress.

- The limiting deforming force below which a body retains its property of elasticity and above which it loses its property of elasticity is called the limit of elasticity.
- The point on the stress-strain curve beyond the elastic limit where after the material continues to deform without an increases in load in known as the field point.
- The stress at yield point Y is called yield strength/stress.
- If there is large plastic deformation in between yield point and breaking point, the metal is said to be ductile.
- If the wire breaks into piece on reaching beyond elastic limit, it is called brittle.
- Tension and compression (Young's modulus) $$\text{Y} = \frac{\frac{\text{F}}{\text{A}}}{\frac{\Delta l}{l_{0}}}.\\\text{The unit of Y is Nm}^{\normalsize-2}.$$
- Work done is stretching a wire,

$$\text{W} =\frac{1}{2}×\text{F}×\Delta l$$

- Energy stored per unit volume of the specimen

$$=\frac{1}{2}×\text{stress × strain}$$

- Bulk modulus

$$\text{k} =\frac{\text{stress}}{\text{strain}}=\frac{\Delta p}{(-\Delta \text{V}/\text{V})}$$

- Modulus of Rigidity (η),

$$η =\frac{\text{F/A}}{\Delta \space \text{l/l}}$$

- Compressibility is reciprocal of bulk modulus,

$$\text{C} =\frac{1}{k}$$

- Poisson's ratio is defined as,

$$\sigma =\frac{\text{Lateral strain}}{\text{Longitudinal strain}}\\=\bigg(-\frac{\Delta \text{r/r}}{\Delta\space l/l_{0}}\bigg)$$

**Factor affecting elasticity of a material**

(i) Hammering and rolling

(ii) Annealing

(iii) Effect of the presence of impurities

(iv) Effect of temperature

**Application of Elastic Behaviour of Materials**

(i) In designing a building, the structural design of columns, beams and supports

(ii) Use of wire-ropes in cranes

(iii) Design of bridges