The ratio of longitudinal stress σ (force F divided by area A, i.e. σ = F/A) to longitudinal strain (change in length δL divided by original length L, i.e. δL/L) in the presence of lateral strain: E = (F/A)/(δL/L). If there were no lateral strain, Young's modulus would be equal to the axial modulus.
Subjects: Earth Sciences and Geography — Mathematics.