The magic gravity saves the day!
Not....
Gas pressure wins every time....
The external higher atmospheric pressure air is trying to get to (i.e equalize with) the tiny bit of lower pressure air inside the glass above the water when it is turned upside down. ....and if the seal is broken the air rushes upward to the low pressure area above the water....pushing the water out of the way....before it starts to leak out.
Simple demonstrable proof that air pressure wins over any "gravity"....every time....
You assertion is false Afoaf.
Atdabeach....I think your suggestion that we should be able to measure higher pressure on the bottom wall / floor of the container vs the sides...if gravity does indeed hold earth's atmosphere from equalizing with the vacuum of space....is a good one. Good luck with that indeed.
Unless the claim is demonstrated by experiment....it's wrong.
Anyone want to tackle the mechanical gyroscope as a horizon indicator for flying around a curved surface problem?
Seems it's being avoided for some reason.....hmmmm?