a) Tensile stress and strain

c) stress, strain and ultimate tensile strength

di) Young modulus = tensile stress/tensile strain, E = σ/ε

tensile stress = the force applied on a material per its unit cross-sectional area

σ = F/A

• tensile stress (Pa) = force applied on a material (N) / cross-sectional area (m)

tensile strain = the ratio of the extension to the original length of a material under tensile stress

ε = x/L

• tensile strain = extension (m) / original length (m)

before the limit of proportionality → σ ∝ ε

ultimate tensile strength = the maximum stress that a material can withstand before breaking

young modulus = the ratio of tensile stress to tensile strain of a material before the limit of proportionality (the stiffness of a material)

E = σ/ε

• young modulus (Pa) = tensile stress (Pa) / tensile strain

only the material of an object affects its young modulus