Matching a metal to its use

1. Every use of a metal places demands on it, such as being light, carrying a current or surviving contact with water.
2. The metal chosen is the one whose physical properties best meet those demands.
3. Four properties explain the main uses of aluminium and copper: density, electrical conductivity, ductility and resistance to corrosion.
4. A full explanation of a use names the metal, the use and the property, and then says how that property helps the product do its job.

Aluminium in aircraft

1. Aluminium has a low density of about $2.7{g/cm}^3$, compared with about $7.9{g/cm}^3$ for iron and about $8.9{g/cm}^3$ for copper.
2. A metal with a low density gives a part of a particular size a small mass.
3. Aircraft bodies and wings are made mainly from aluminium, because its low density keeps the mass of the aircraft as small as possible.
4. A lighter aircraft needs less fuel to take off and to stay in the air, so it is cheaper to run.
5. Burning less fuel also means that less carbon dioxide is released on each flight.
6. Iron or copper parts of the same size would make the aircraft roughly three times heavier, and it might not be able to take off at all.

Aluminium in overhead power cables

1. The thick cables that hang between pylons and carry electricity across the country are made from aluminium.
2. Aluminium is a good electrical conductor, so an electric current passes along the cable easily.
3. Aluminium also has a low density, so a long cable is light enough to hang between pylons without sagging badly or snapping under its own weight.
4. Copper conducts electricity even better than aluminium, but copper is more than three times as dense.
5. An overhead copper cable would be so heavy that stronger pylons would be needed, placed closer together, and the copper itself would cost more.
6. Aluminium is therefore chosen because of two properties working together: low density and good electrical conductivity.

Aluminium in food containers

1. Aluminium is used for food containers such as drinks cans, takeaway trays and kitchen foil, because it is resistant to corrosion.
2. Food and drink are often damp, salty or slightly acidic, and these conditions make many metals corrode.
3. Aluminium resists this corrosion, so the container does not weaken or leak, and metal compounds do not get into the food.
4. An iron container would be a poor choice, because iron corrodes quickly in contact with water and air.
5. Aluminium foil and trays are also light and easy to shape, but the property that explains their use for food is their resistance to corrosion.

Copper in electrical wiring

1. Copper is used for the electrical wiring in homes, appliances and electronic devices.
2. Copper is a very good electrical conductor, so current flows through the wire with very little resistance.
3. Copper is ductile, so it can be drawn out into long, thin wires without breaking.
4. Both properties are needed, because a metal that conducted well but snapped when drawn out could never be made into wire.
5. Copper wire is also malleable, so it can be bent around corners and into terminals without cracking.
6. Inside a cable, each copper wire is covered with plastic, because plastic is an electrical insulator and stops the current from reaching anyone who touches the cable.
7. The density of copper matters much less here, because wires in a building are short and are supported along their whole length.