What is the relationship between altitude and density?

The relationship between altitude and density is characterized as inverse. As altitude increases, air density decreases. This phenomenon occurs because the atmosphere is held by gravity, and as one moves further away from the Earth's surface, the weight of the air above decreases, resulting in lower pressure and therefore lower density at higher altitudes.

In simpler terms, at higher altitudes, the molecules are more spread out due to lower atmospheric pressure, leading to a decrease in the density of the air. This relationship is crucial in aerodynamics, as it affects aircraft performance, lift, and engine efficiency at various flight levels. Understanding this inverse relationship is essential for calculations involving flight dynamics and designing aircraft systems that operate effectively across various altitudes.