Stress, Strain & Elasticity — A/L Physics

What must I remember about Stress, Strain & Elasticity?

• Elasticity Concepts: Property of a material body to regain its original size and shape upon removal of deforming forces; Plasticity refers to permanent deformation without recovery.
• Stress (σ): Internal restoring force per unit cross-sectional area: Stress = F / A (scalar, SI units N/m² or Pascal Pa); Types: Tensile/Compressive stress (normal to area) and Shear stress (tangential to area τ = F_tangential / A).
• Strain (ε): Fractional deformation produced by stress: Tensile/Compressive Strain = ΔL / L0 (dimensionless); Shear Strain = tan θ ≈ θ (radians); Volumetric Strain = ΔV / V0.
• Hooke's Law: Within the proportional limit, tensile stress is directly proportional to tensile strain: Stress ∝ Strain => σ = E * ε, where E is an elastic modulus.

Test yourself (1 minute)

1. Stress-Strain Curve Features

   1) Proportional Limit (Hooke's law strictly obeyed); 2) Elastic Limit / Yield Point (beyond which permanent plastic deformation sets in); 3) Ultimate Tensile Strength (UTS, maximum stress material can bear); 4) Breaking / Fracture Point.

2. Ductile vs Brittle Materials

   Ductile materials (copper, mild steel) exhibit extensive plastic deformation range between yield point and fracture; Brittle materials (glass, cast iron) fracture abruptly with negligible plastic strain just past elastic limit.

3. Elastic Hysteresis

   Energy dissipated as heat per unit volume during a cyclic stress-strain loading and unloading cycle, represented by the enclosed loop area on stress-strain plot (prominent in rubber, used in shock absorbers).

Practise Stress, Strain & Elasticity questions today

Source: NIE G.C.E. (A/L) Physics Resource Book - Unit 10: Mechanical Properties of Matter

What comes next?

Next in the syllabus

Where does Stress, Strain & Elasticity fit in the syllabus?

Unit 10.1 · Year 2 · Term 3