I have no bias in this discussion, I've always said that I KNOW nothing. I only base my opinions on what I perceive within my own environment. I do not for one moment profess to have the answers. And I have the dignity to admit that your "fly example" has got me a little stumped. I can see your point of view with regards to the environment moving with the 'object'. But I'm not sure the inside of a car and the earth can be compared. But I will again admit that you've given me food for thought there. I will think about it and get back to you my friend. And when I say think I don't mean look for a way out of it, I will do what I always do and look at both sides with an open mind
Your somewhat humble opinion and will to actually debate is the sole reason I botherd to actually reply to this post in the first place so for that part I salute you. I'm willing to debate anything, how stupid I still might find it on a personal level, as long as it's kept open minded, actual facts and logic arent ignored. I'm no physicist myself, but consider myself somewhat educated on the subject just from pure interest and curiousness as it effects us and everything around us on a daily basis. Maybe I could and should have went into more details on the aeroplane matter, considering my father actually was a pilot I'm quite familiar with planes. Though that question might actually be answerd now (with the train, fly etc)and its the followup on why the air is moving that's the issue to actually acknowledge the first question.
Also I appologize in advance for maybe not using the correct words and/or terms here, as well as spelling, cause english is not my native language. From my point of view I'm probably not the most suited to explain this either, as from experiance (regarding any possible subject) one can learn enough to understand something on a personal level, but to explain or teach something to someone in a good and easily understandable way you need to know it 10x deeper.
Doing my best to try and come up with analogies or examples that you could actually try for yourself, as I think that would be the way for you to actually feel sure about something, if you as you say base your understanding on what you percive.
You are the right the chalk line would not move. Only because I would not be in the air long enough to lose speed. If I could hover I would appear to move towards the back of the train as I slowly and steadily lost the momentum built up from being propelled by the FLOOR of the train. If what you say is correct, that the air around the earth is spinning with it, what do you propose is propelling the air? It must be a very clever force, one that can move heavy dense matter such as concrete, iron and rock and at the same time, light gaseous material at exactly the same rate whilst applying the same uniform force? Physics denies you my friend
The chalk outline would not move even if you, and sadly we can't really test this as we as humans can't hoover, managed to hoover in the train for 1 hour. The fly in the car might actually be a better example. But there's a couple of other things you could try. Take a helium filled balloon onto the train (or maybe even better, in your car), that you just hold in a thing string, fishing line or the like. That balloon would essentially be hoovering in the car/train and you could see how it behaves. If what you said was correct the line your holding it in would not be vertical when the speed is constant, and the balloon would slightly pull towards the back of the train, it does not, I can assure you but feel free to try for yourself (asuming constant speed, no open windoes or other kind of forced airflows within the train/car due to say ventilation). You could see another cool thing if you do this properly with a helium ballon in your car as well, that when you accelerate the balloon would actually move forward instead of backwards, and move backwards when you brake (completly reverse to the way you feel or see any other objects behave in the car that have higher density then air).
You could try the same thing with one of thoose new popular small drones/queadcopters, if you somehow was allowed to fly it on a train
As a third thoughtexperiment: Say we could actually get a traincart the size of a hangar, big enough to fly a model RC airplane in it. Even if that train was moving at 200mph (constant speed) it would be no different flying the model RC plane in there, then in a stationary hangar (same as the fly in the car).
Regarding the air spinning. I'm not sure I know all the correct terms and principles in english words to explain this properly but I can give it a try. Its also hard to come up with (at least for me) a good analogy for this that you could just step outside your front door and try/see, as we're talking about things on such a big scale.
The short answer, gravity and inertia. You might have played with toys like this?
http://cdn2-b.examiner.com/sites/default/files/styles/image_content_width/hash/10/09/10095f855a05759f17e9da5b5f0b840b.gif?itok=dSLvbtee You spin it on a table either with you fingers or a string, and it will spin for quite a while before coming to rest (it also show the principles of angular momentum, but thats a different matter all thoghter and not really of any importance to this discussion (the reason why it doesn't fall over while spinning)). It could actually just as well be a marble that we set spinning on the table, for this purpose. Why does it slow down? Two main things, friction on the table where its spinning, and drag in the air. But if we put the marble inside a little glas sphere with vacuum in it, and managed to levitate the marble inside that glas sphere so the marble is just floating inside that vacuum. Now if you started spinning it, it would essentially spin forever, there's nothing slowing it down. This is where we have the earth, the marble beeing earth and the vacuum sphere space, as there's vacuum in space and earth isn't resting on anything there's nothing slowing us down, not even the air/atmosphere on earth however "light/thin" you consider air to be, there is no friction on the outside (space) effecting the air.
Thanks to gravity, that's pulling the air down towards earth however, there's quite the friction between just our air and the ground. How small this friction ever could be percived on a human level if you just go outside doesn't really matter, as there is none, nada, absolutly no friction on yhe outside of the earth towards space. Air does provide quite the friction/drag even if mostly think of it as "nothing", just put you hand out the window going 60mph, quite the force on your hand.
The friction between the actual earth/ground and our air/atmosphere is rather irrellevant for this point though, as they are allready spinning/moving at a constant speed. It would only come into play if we suddenly started to accelerate or decelerate the earth's spin (jumping in the train analogy). I would imagen that the key thing to wrap your head around here is that if we go back to the marble and earth analogy, if you think of the marble and the earth, its the entire earth with the air and our atmosphere that represent the marble, not just the "solid" part of earth that we walk on.
To try and answer your question more direct then regarding the
"If what you say is correct, that the air around the earth is spinning with it, what do you propose is propelling the air?", There is no friction, no force slowing us/earth down (vacum, not resting on anything etc, like the marble levitating in the vacum glass sphere) so once we're spinning we don't need any additional force to keep spinning, we will essentially spin forever.