In high school I've been told that the molecules of gases have generally speed of severals kilometers per second. Hence why the wind is not always present, and why not that fast? (I guess it has to see with the huge number of particles... I never studied such a system in Physics yet, I believe but I might be wrong.) Also why when I open a bottle of perfume I cannot smell its odor if I'm at say 2 meters from it? (It's like the big molecules of perfume cannot move that fast at all since there are too much other molecules or so). Thanks. P.S.: I've asked this question to my teacher when I was younger and it seems he misunderstood the question. Answering that the wind was a depression or something like that. Which do not say why the wind is not as fast as most molecules in air so most molecules forming the wind itself.