Density of air cannot be measured, this size directly is defined by means of formulas. Two types of density of air differ: weight and mass. In aerodynamics most often use the mass density of air.
1. For a start sort out the main concepts. So, the weight density of air is the weight of 1 m3 of air, size is designated by letter g. g = G / v. Here g is the specific weight of air, it is measured in kgf/m3, G is air weight, it is measured in kgf, v is air volume, it is measured in m3.
2. Take into account that air G weight - size changeable and changes depending on various conditions, for example, from the geographic latitude and force of inertia which arises at rotation of Earth round its pivot-center. On poles of the planet of G is 5% more, than in the equatorial zone. Under standard atmospheric conditions, that is with a barometric pressure of 760 mm Hg and temperature of +15 °C, 1 m3 of air has weight density of 1.225 kgfs.
3. Remember that the mass density of air is a weight of 1 m3 of air, size by the Greek letter of river It is known that body weight – a constant is designated. Unit of mass it is considered to be the mass of the weight from iridisty platinum which is stored in the International Board of Weights and Measures in Paris. The mass density of air r is calculated on a formula: р = m / v. Here m is the mass of air, v is its density. Mono to determine the mass density of air, knowing its weight density on a formula: p = v / g.
4. Note that density of air is capable to change when its pressure and temperature change. At the changing indicators the mass density of air is calculated on a formula: p = 0.0473 x V / T. Here In - barometric pressure, is measured in mm Hg., T-air temperature, is measured in Kelvins.
5. Keep in mind that density of air increases with increase in pressure and fall of temperature. In this regard, the greatest density of air happens in frosty weather, and the smallest – during heat. Density of damp air is less, than dry. The it is higher than a distance from the earth, the air density as pressure at the same time too decreases is less.