The slinky thing has to do with tension. Also, this
TL/DR: Things fall because they are heavier than the air they exist in
INB4 - why dont things float in a vacuum?
Answer - because you've only changed the medium the object exist is - not the object itself.
is a completely nonsensical statement. Air is compromised of gases (like nitrogen, carbon dioxide, and oxygen), which have mass as there are atoms in it which can push against things. Remember f = ma? Force = Mass x Acceleration. In order for a force to act on an object to move it in a direction, there must exist some non-zero amount of mass accelerating in that direction. Thus, it is at least theoretically possible for your claim that air is pushing objects down to be true if there was enough mass and downwards acceleration. However, a vacuum has NO mass; there are NO atoms in it to push back against the atoms comprising things like a tennis ball. Thus, if the tennis ball still falls down while its in a vacuum tube, then there must be some other force acting on it to pull it in that direction which has NOTHING to do with the atmosphere physically pushing it downwards.
Edit - I'd like to note that this explanation doesn't actually prove gravity exists, as it could still be some other force causing it (maybe magnetism? :p) All it proves for certain is that your explanation is incorrect.
This post was edited by Magicman657 on Mar 23 2017 03:19pm