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What
do you mean "light"? Everyone thinks of aluminium as "light" and no-one ever questions it, because it all seems so obvious. But if you take a look at a book of physical formulae, you soon find that the silvery light metal is actually a heavyweight. It is first necessary to explain the key concept here, namely the "density" of a material. This describes the ratio of mass to volume, that is how heavy a material is relative to its size. The unit of physical density is kg/m3, but grams per cubic centimetre (g/cm3) is also used. Water, for example, has a density of almost 1.0 g/cm3 (precisely: 0.998). If we look at the metals, aluminium's density of 2.7 is very low compared to that of stainless steel at 7.9 or brass at around 8.4. However, there are also some materials which make aluminium look really heavy. Glass, for example, has a density of around 2.6, which means that "glass is lighter than aluminium!" The next shock is, "marble weights exactly the same as aluminium"; that is marble has the same density as aluminium at 2.7. So why do we think aluminium is light? Because of the way it is used in practice. Products or parts in aluminium are often made as hollow constructions or also as foils or in thin sheets. We rarely encounter aluminium in solid plates or bodies. It is therefore true: aluminium is a light metal, but it is not a light material.  Overview |
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