- if there is no wind, air particles are still moving, but we take the average movement on all point we get a field of null velocities.
- given this answer, it seems that NASA call "air particles" a fluid particles and not real particle, but I'm not quite sure.
In short, is the NASA definition making confusion between "streamline" and "line of flow", "air particles" and "small volume of air containing several air particle whose average movement follow a streamline"? Are the terms used by NASA the correct one?
EDIT: I asked NASA and they respond with a redirection to a definition that speaks of flow and "massless particle" without defining either one. Yet speaking of "massless particles" clearly states they are not actual air particles. I still feel as if I'm in front of circular definitions, concept A defined by concept B, and concept B defined by concept A, if ever defined.