The coin can be at any angle and the environment has no air friction
123923
We have to insure that the coin is fairly weighted. (if one side is heavier then the other, it could land wrong.)  The horizontal surface must be completely flat.  The coin should be dropped on edge, in a repeatable fashion. (So that whatver drops it isn't angling it or affecting it.
250418
The vertical rise must not exceed the head of water, or the riser will not work.
577588
absistence will cost you nothing.
85042
yes it means that the system is either in equilibrium or no force is being appplied on the point.(i.e. , no charge is present)
154590
NO BALL.\nIT NEVER CHANGED.
585392
In cash, no checks, credit cards or pop bottles.
2915
It's kind of neat. Only a round cover will not fall through the hole it covers. Any other shape, if turned the wrong way can slip through the hole and fall.
125941
There is no smoke. It's electric.
479841
the weight of the object has nothing to do with it.
596104
You float without weight there.
415008
it's clean,not expensive,nonexplodable,and environmental friendly.
319441
the servant,  there are no corners in a circular room
122618
Imagining the world with no hypothetical situations is a hypothetical situation itself.  It's an impossible paradox.
417057
because that defies the laws of inertia and motion
411995
It is a ratio so there are no units.
503908
There is no danger at all.
79881
Never heard of this one.  I would venture to say that this would be caused by vibrations picked up through the liquid on which the block floats causing the block to randomly tip.  If it slides the coin enough in one direction it will continue in that direction because of gravity and eventaully fall off.