I have a few questions that share a similar theme. 1) Is wind just fast-moving air particles? 2) When you're in a stationary car and it begins to move, does the back of the car push the air particles inside the car forward (I know they're always moving but is there some sort of net movement so that relative to the car, it's no longer moving?) 3) If you have a balloon floating in a car (let's say it's not touching anything) and the car accelerates, if the acceleration is great enough, would it be possible that the air particles being pushed to the front be enough to move the balloon a little? 4) So assuming that this is how wind works and if we can treat the air particles this way, if a really long train with a really long, narrow opening rolled past and you stuck your arm inside the opening, would you feel the the force of the air particles inside the train moving against your arm like a wind (assuming very little seeping)? Would it roughly the same speed as the train?