Properties of Materials

≈ 20 min

An object is a thing; a material is what it is made of. A spoon is an object; steel, wood or plastic is the material.

Every material has properties — measurable or testable characteristics:

Property	What it means	Test
strength	resists breaking under a load	hang masses until it fails
hardness	resists being scratched	scratch it with another material
flexibility	bends without breaking	bend it and let go
brittleness	shatters instead of bending	tap it sharply
thermal conductivity	lets heat pass easily	heat one end, feel the other
electrical conductivity	lets electricity pass	put it in a circuit with a bulb
water resistance	does not absorb water	drop water on it

Engineers and designers do not pick materials by preference — they match the property to the job.

Worked example — a cooking pot. The base must move heat quickly from the stove plate into the pap, so it is made of a metal like steel or aluminium: high thermal conductivity. The handle must not move heat into your hand, so it is made of wood or a hard plastic: low thermal conductivity. The same object uses two materials with opposite properties, because it has two different jobs.

The same reasoning explains a household cable: copper in the middle (excellent electrical conductor) wrapped in plastic (excellent electrical insulator, so the current stays in the wire and you stay safe).

Why are the handles of cooking pots usually made of plastic or wood rather than steel?

Because plastic and wood are stronger than steel

Because plastic and wood are poor conductors of heat, so the handle stays cool enough to hold

Because steel is too expensive to use for a handle

Because plastic and wood are heavier, which balances the pot

What is the name for a material that lets heat pass through it easily?

A learner rubs a steel nail across a tile, then across a piece of glass, and records which surface gets a mark. Which property is she testing?

Flexibility

Hardness

Electrical conductivity

Water resistance

A learner tests how far a nylon fishing line stretches. She finds it stretches 2 mm for every 500 g she hangs on it. If the stretch keeps following the same pattern, how many millimetres will it stretch when she hangs 2 kg on it?