... >> Natural Science >> Chemistry >> Expansion
Definition: The increase in volume of a body as a result of changing conditions, normally increasing Temperature or decreasing Pressure, the latter being more important for Gases. Contraction is the reverse process. In most solids and liquids, increasing temperature increases the random thermal motion of their atoms, which tend to move apart, ie expansion occurs. The amount of expansion is usually expressed as a coefficient of expansion – the fractional change in length or volume per unit temperature change – and is specific for a given material. Water is unusual in that it expands on cooling from 4 C to 0 C. This means that ice floats on water at 0 C and rivers freeze from the surface downward.
Source: Illustrated Dictionary of Science, Andromeda. London: Andromeda, 1988. Credo Reference. Web. 08 August 2012.