Materials and their properties
What this domain tests
Materials questions test whether you can classify materials, match properties to service conditions and justify a choice with evidence, not just name a material.
Classification and properties
- Timber: hardwood from broad-leaved trees (oak, beech, ash); softwood from conifers (pine, spruce). The terms describe botany, not hardness.
- Metals: ferrous metals contain iron (steel, cast iron) and are magnetic; non-ferrous metals include aluminium, copper, brass and titanium.
- Polymers: thermoplastics soften on reheating (PP, HDPE, acrylic, PVC); thermosets cure permanently (epoxy, polyester resin, melamine); elastomers are rubber-like.
- Composites: two materials combined so the properties are better than either alone (GRP, carbon fibre; MDF is a wood-based composite). Define properties precisely: strength in tension, compression and bending; stiffness; hardness; toughness; malleability (hammered into shape); ductility (drawn into wire); conductivity; thermal expansion; density; corrosion resistance.
Worked example
A toy hammer for a nursery. The head needs toughness and impact resistance and must be non-toxic; the handle needs stiffness and a smooth, splinter-free surface. Beech is hard, tough and takes a safe finish, but a solid beech head is heavy for a toddler and can bruise. Polypropylene is tough, low-density, colour-fast and can be injection moulded with a soft-touch overmould, so the head and handle are specified in PP. A steel head would be durable but fails the safety criterion. The reasoning is criterion-led: safety and mass rule out metal before cost is considered.
Traps
- Saying a softwood is always softer than a hardwood.
- Calling a thermoplastic a thermoset.
- Giving a property without linking it to the product’s use.
- Forgetting finishes, joints and manufacturing method when justifying a choice.