Topic 6: One-Page Revision Sheet

Chapter 6: Mechanical Properties of Solids – One Page Revision

1. Mechanical Properties of Solids

Study of behaviour of solid materials when external forces are applied to them.

2. Elasticity

Property of a material to regain its original shape and size after removal of deforming force.

Plasticity

Property of a material to undergo permanent deformation.

3. Stress

Internal restoring force per unit area developed in a body.

Stress = Force / Area

SI unit: Pascal (Pa)

Types of Stress

• Longitudinal stress
• Volumetric stress
• Shearing stress

4. Strain

Ratio of change in dimension to original dimension.

Strain = Change in dimension / Original dimension

Strain has no unit.

Types of Strain

• Longitudinal strain
• Volumetric strain
• Shearing strain

5. Hooke’s Law

Within elastic limit, stress is directly proportional to strain.

Stress = k × Strain

k = Modulus of elasticity

6. Stress–Strain Curve

• Straight line region → Hooke’s law valid
• Proportional limit → stress ∝ strain
• Elastic limit → body regains original shape
• Yield point → plastic deformation begins
• Breaking point → material breaks

7. Young’s Modulus (Y)

Ratio of longitudinal stress to longitudinal strain.

Y = (F / A) / (ΔL / L)

Y = (F × L) / (A × ΔL)

SI unit: Pascal (Pa)

8. Nature of Young’s Modulus

• Measures stiffness of material
• Higher Y → more rigid material
• Lower Y → more elastic material

9. Important CET Points

• Definitions of stress, strain and elasticity
• SI units of stress and Young’s modulus
• Hooke’s law validity
• Identification of points on stress–strain curve
• Numericals using Y = (F × L) / (A × ΔL)