Density, $ \rho$

Density is defined as mass per unit volume of the substance. However, as discussed before, in the spirit of Continuum Hypothesis, it is defined as a limit. If $ \delta m$ is the mass of a small volume $ \delta \forall$ then

$\displaystyle \rho = \lim_{\delta \forall \rightarrow \delta \forall_0} {\delta m \over
 \delta \forall}$ (1.13)

Unit of density in the SI system is $ kg/m^3$ Under ordinary conditions the density of water is $ 993 kg/m^3$ while that for air at $ 15^0$C and atmospheric pressure is $ 1.23 kg/m^3$.

Density of liquids is somewhat insensitive to the changes in pressure and temperature. For gases there is a strong dependence of density on these quantities and is given by the equation of state of the particular gas.



Subsections

(c) Aerospace, Mechanical & Mechatronic Engg. 2005
University of Sydney