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Microlight » Meteorology » Air Density

Air Density

The density of the atmosphere is the mass of air per unit volume. 

Under ISA conditions, the density at mean sea level is 1.225 kg/m3.

Variation of Density with Height

The force of gravity attracts the air molecules to the surface of the earth and compresses them close together. 

As height is gained, and air pressure decreases, the number of molecules in a cubic metre decreases (the air becomes less dense), and at 20,000 ft the density is approximately half its sea-level value.

Variation of Density with Temperature

Warm temperatures cause molecules to spread out so that density is low.

Cold temperatures encourage molecules to group together so that density is high.

With INCREASING ALTITUDE:

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