Investigating the elastic and plastic extension of metal wires

In the experiments P7.1.4.1 and P7.1.4.2, the extension of iron and copper wires is investigated by hanging weights from them. A precision pointer indicator or the rotary motion sensor S attached to a CASSY measures the change in length Δs, i. e. the extension

After each new tensile load

the students observe whether the pointer or the rotary motion sensor returns to the zero position when the strain is relieved, i.e. whether the strain is below the elasticity limit σ_ε. Graphing the measured values in a tension-extension diagram confirms the validity of Hooke's law

up to a proportionality limit σ_p.