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Thermal expansion is a key design consideration when building a road over a bridge since the length of the bridge varies with temperature (seasonal changes) causing the pavement to crack.

Density determines how much something weighs with respect to its volume and this knowledge can be used to optimise various components, for example with engine parts in automobiles.

A lot of thermal expansion knowledge
goes into building a bridge like the one above.

Thermal expansion plays its part in material design and manufacture in industrial sectors such as aerospace, automotive, construction, food and the environment. This is true of density too since as materials expand they become less dense. Expansion and density are inversely proportional to each other (ρ= m / V).

Common applications of thermal expansion and density

Detection of structural changes in crystalline structure Accurate length determination (metrology) Thermometers (bimetal thermometers, mercury thermometers) PVT-diagrams Metal processing: casting, moulding Material design Building industry Process simulations Aerospace and automotive industry		Clinical thermometers use the thermal expansion of a liquid (alcohol or mercury) to indicate temperature.

		The metre was originally defined by the length of a platinum-iridium bar kept in Paris (see picture above) which had to be maintained at a uniform and stable temperature to prevent length changes.
Metal thermal expansion measurements showing length increasing with temperature.

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