What happens to air density as altitude increases?

As altitude increases, air density decreases. This phenomenon occurs because the atmospheric pressure diminishes as one moves higher into the atmosphere. At higher altitudes, there is less air above a given surface than at lower altitudes, which results in a lower weight of air pressing down and consequently a decrease in air density.

Factors contributing to this decrease in density include the reduced number of air molecules per unit volume as you ascend and the fact that the atmosphere becomes less compressed at higher altitudes. This understanding is crucial in fields such as aviation and meteorology, as it affects factors like aircraft performance, weather patterns, and the behavior of unmanned aerial vehicles (UAVs).

The other choices do not accurately reflect the behavior of air density with altitude. Air density does not increase or remain constant with altitude, nor does it fluctuate significantly; it consistently decreases as altitude rises.