CPL » Principles of Flight (H) » The Atmosphere
24.4 The Atmosphere
24.4.2 Define air density.
Air Density ρ (rho), is a fundamental property of the atmosphere.
It refers to the amount of mass per unit volume of air.
In other words, it is a measure of how much air molecules are present in a given amount of space.
At sea level at standard temperature and pressure, air density is 1.225 kilograms per cubic metre (kg/m³).
24.4.4 Describe the effect of temperature, pressure and humidity on air density.
Air Density is affected by temperature, pressure, and humidity.
- temperature increases = density decreases
- pressure increases = density increases
- humidity increases = density decreases
24.4.6 Describe the normal changes in pressure, temperature and density with increased altitude.
Air is compressible so the atmosphere is more dense at lower levels because the weight above compresses the air molecules.
As you go up in altitude, the amount of molecules in the air decreases, so less pressure.
Less pressure = Lower density
With increasing altitude, density decreases because the decrease in pressure overrides the decrease in temperature.
24.4.8 Describe the International Standard Atmosphere.