Fig. 2.5. Influence of the state variables on the density of air

The density of air decerases with the altitude as the density is directly proportional to the atmospheric air pressure as shown in Eq. (2.1). The variation in the air pressure with the altitude is shown in Fig. 2.6.

Fig. 2.6. The variation of air pressure with altitude at 15° c tempertaure and 0% humidity