AQA 7408 A Level Physics · Mechanics and Materials
Materials and Young Modulus
Distinguish material properties from sample dimensions by using stress and strain rather than force and extension alone.
Stress, strain and stiffness
Tensile stress is force divided by cross-sectional area; tensile strain is extension divided by original length. Young modulus is stress divided by strain in the linear elastic region and has unit pascal.
Graph interpretation
The gradient of a force–extension graph is the stiffness of that sample. The gradient of a stress–strain graph is Young modulus. The area under a force–extension graph is the work done deforming the sample.
Practical reasoning
Measure the original length and diameter carefully, repeat diameter measurements in different orientations and avoid parallax when reading extension. Stay below the elastic limit when determining Young modulus.