# Mechanical properties of matter

• stress, strain, Young modulus
• force-extension graphs, energy stored

For many students, this topic will be the first time in physics they have been asked to explicitly link microscale structure (molecular bonds) with observed behaviour (stiffness and other characteristics). Their familiarity with the language used will vary depending on previous study, which will include design and technology, engineering and science. It's often worth spending a little time making sure that everyone is happy using the scientific terms precisely, as many of them have everyday uses which are not quite correct. You may like to remind them that they already know the terms mass, weight and gravity are used in a very particular way by physicists; the terms stiffness, stress and strength are the same. A possible structure might include:

• to recap Hooke's Law and other previous work done describing the behaviour of materials that stretch
• having students calculate stiffness of lab springs/materials using obtained data and apply experimental language to their work
• being precise when introducing and defining the terms stress and strain. You can show how they are related by the Young modulus for a given material, and how this is independent of the shape of the sample
• checking understanding of mathematical relationships, units and symbols is a good opportunity to discuss techniques for revision, as well as having a clear physics benefit
• students taking practical measurements to calculate Young modulus and compare this to accepted values
• discussing the relevance of material characteristics to their uses, being sure to include a range of applications from prosthetics, sports equipment design and consumer products as well as civil engineering
• students are often keen to use simulations and computer models in design and analysis; discussions of the benefits and limitations of this can be illuminating
• students being confident with the derivation and calculation of energy stored by a spring and knowing they must be able to find an approximate answer by using the area under a force-extension graph

Whilst this list provides a source of information and ideas for experimental work, it is important to note that recommendations can date very quickly. Do NOT follow suggestions which conflict with current advice from CLEAPSS or recent safety guides. eLibrary users are responsible for ensuring that any activity, including practical work, which they carry out is consistent with current regulations related to Health and Safety and that they carry an appropriate risk assessment. Further information is provided in our Health and Safety guidance.