What is the relationship between altitude and air density?

The relationship between altitude and air density is that air density decreases with altitude. As you climb higher in the atmosphere, the weight of the air molecules above you decreases, leading to a reduction in pressure and density. This is because the atmosphere is held to the Earth by gravity, and as you go higher, there is less atmosphere exerting pressure, which results in fewer air molecules per unit volume. Consequently, as altitude increases, the air becomes thinner, meaning there are fewer molecules of air, which translates to lower density.

This concept is critical for pilots because it affects aircraft performance. For instance, as air density decreases, engine performance and lift generated by the wings can deteriorate, impacting takeoff and climb rates. Understanding this relationship helps pilots make informed decisions about flight operations at different altitudes.