Upside-Down Water Phenomenon

Discussions center on a physics puzzle or GIF showing water not spilling from an inverted bottle or cup, with debates on mechanisms like atmospheric pressure, vacuum, surface tension, siphons, and air bubbles.

📉 Falling 0.3x Science
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Keywords

AFAIK YMMV i.e water air cap drops bowl tension beneath select opening gravity

Sample Comments

aspaviento Sep 10, 2021 View on HN

What about... turning it upside down and let graivity do its job?

sixtypoundhound Oct 27, 2012 View on HN

Is this a case of water finding it's own level?

tantalor Feb 26, 2023 View on HN

Doesn't model air pressure, so no siphon :(

richardfey Nov 6, 2021 View on HN

I wonder if it has something to do with surface tension

JWLong Dec 3, 2010 View on HN

Please expound upon why it doesn't hold water...

amelius Jun 9, 2018 View on HN

Wouldn't this design create a vacuum in the reservoir?Edit: (reservoir = bottle)

zeristor Jul 13, 2025 View on HN

Wouldn’t the end up floating into the air?

aprao Mar 23, 2018 View on HN

That's an informative but unsatisfying gif. What if the residue on the top leaks down?

barrkel Jun 1, 2014 View on HN

If the siphon is in the middle of the cup, it won't be activated by tipping, because tipping won't increase the level at the centre.

m0zg Dec 9, 2019 View on HN

I don't think this would work without air.