Here's why:

* Gas dynamics focuses on the behavior of gases in motion, including their properties, forces, and energy transfer.

* Aerodynamics, a closely related field, specifically deals with the motion of air and other gases around objects.

However, gas dynamics encompasses a broader range of phenomena beyond just air, including:

* Compressible flow: When the speed of gas flow is high enough to cause significant changes in density.

* Rarefied gas dynamics: When the gas molecules are far apart and their collisions are infrequent, such as in high-altitude flight.

* Plasma dynamics: The study of ionized gases (plasma), which are influenced by electromagnetic fields.

So, while aerodynamics is a key aspect of gas dynamics, the latter is a more general term encompassing all aspects of gas motion.