6.1.5—The terms stress, strain and the Young modulus
- Syllabus
- 9702–2028–2029
- Objective
- 6.1.5
- Level
- AS
Stress is force per area, strain is extension per original length, and Young modulus links them
Stress σ=F/A and strain ε=x/L are dimensionless ratios of deformation. Young modulus E=σ/ε measures a material’s stiffness in the linear elastic region.
Use cross-sectional area and original length, not the deformed dimensions, and keep stress in pascals.
A wire’s stress doubles if the same force acts on half the area; its strain depends on extension relative to its starting length.
Strain has no unit, while stress and Young modulus are measured in Pa; Young modulus is not the same as spring constant.
ConceptA-Level CAIE Physics AS