How does a Pythagorean Cup work?
A Pythagorean Cup - also referred to as Greedy Cup or Tantalus cup - punishes the greedy because all contain runs out if you fill it too full.
This is because the cup special construction. In the middle of the cup stands a pillar with a pipe running from the cup interior bottom, all the way up through the column and back down to the cups outer bottom.
The pipe acts as a siphon sucking out the contents of the cup when the liquid is higher than the pipe’s top point.
The siphon works only when the pipe is filled with liquid, so just take it easy on the vine and nothing will happen. when you are modest and do not overfill your cup, you can drink from it as if it was a regular cup.
Affected by gravity
When the liquid goes up to the upper point in the pipe and then flows down to the bottom of the cup, gravity will act more strongly on the long column of liquid, which flows down and out of the cup, than at the short column that stops inside the cup.
The gravity pulls more in the long column, so the pressure in the pipe is less in the upper part of the column. Therefore, the air pressure on the liquid surface, will push the liquid up the tube, and the liquid will continue to flow out as long as the cups liquid level is higher than the discharge location, which is located at the bottom of the cup.
Uses the same principle as toilets
Some modern toilets operate on the same principle: when the water level in the bowl rises high enough, a siphon is created, flushing the toilet.
The moral in this cup is obvious, don’t overfill anything in your life, or you might lose it all.
Image By Materialscientist (talk) – I (Materialscientist (talk)) created this work entirely by myself., CC BY-SA 3.0, https://en.wikipedia.org/w/index.php?curid=24162737