A greedy cup
How to make a Pythagorean cup at home
It’s a cup that spills your drink when you get too greedy!
- test tube;
Cut the bottom off of a plastic bottle. Bore a hole in the cap and insert a straw approximately halfway. Put a test tube on the straw, making sure there is a small gap between the base of the test tube and the top of the straw. Use plasticine to seal the straw and cap together. Pour water into the resulting “cup” so that it doesn’t quite reach the top edge of the straw. So far, so good. But as soon as you add more water, it starts pouring out of the cup – and will continue to drain until it’s all gone!
The Pythagorean cup (also known as the greedy cup) was invented by Pythagoras, an ancient Greek mathematician and philosopher. Legend has it that it was originally intended to help people drink in moderation, allowing them to fill the cup to a certain level and no more. Filling the cup higher than this set point causes all the liquid to drain out of it. This cup seems quite ordinary, but it works according to the principles of a siphon. The straw and test tube form a channel, one end of which leads out the bottom, and the other into the cup's interior. As soon as the liquid level rises above the upper edge of the straw, the siphon engages. As the water filters out, the pressure in the test tube above the straw is slightly lower than atmospheric pressure, and thus atmospheric pressure constantly pushes the flow to continue until the cup is completely empty.