How To Stop The Greedy Cup

hey everyone today i'm going to be showing you a few ways in which you can stop the greedy cup this is also called the pythagoras cup so what i have here is a normal looking cup except in the center there's a protrusion but other than that it's a cup you can see that it kind of has this line at the top this is the fill line if you go past this line it means you're getting a little too greedy and watch what happens if you fill it up too full so you can fill this cup up and you can see that you can fill it up just below the fill line here and nothing happens it acts like a normal cup you can drink it do whatever you want but watch what happens if you get a little bit too greedy and want more in your cup [Music] fill it above the fill line notice it starts leaking out of the bottom of the cup now [Music] what's crazy about this is that it doesn't just go below the fill line now the level of water continues to drop until it drains the entire cup [Music] so if you get too greedy and go past the fill line your cup drains completely this greedy cup is pretty cool so let me show you how it works and then i'll show you how to overcome the greedy cup so that you won't end up spilling the contents of your drink all over the floor if you get too greedy so here's a cross-section of the pythagoras cup or the greedy cup you can see that it has a tube at the bottom that goes up into a u-shape and then goes out the bottom of the cup so what happens as you fill up the cup the water level rises and it will rise up that center u-tube as well but it won't get to the top unless you over fill it past the fill line and once it's past the fill line then the water will start flowing down the other side of the u-shaped tube in there and after that that creates a siphon effect and that siphon effect can now continue until it empties the entire contents of the cup from the top to the bottom now it's rumored that pythagoras actually gave these types of cups to his students and told them where to fill it to he gave him a drink and told him to fill it to a certain line and he didn't tell him what would happen if they went past that line and then he was able to tell which students were the greedy students by the ones that ended up with an empty cup let's see if we can come up with a method to be smarter than the greedy cup now remember that as we're pouring water inside of the cup the water level inside the u-shaped tube will always match the water level outside the u-shaped tube but still inside the cup and that's because of something called pascal's law of communicating vessels it states that no matter what the shape of your container if they're all connected at some point the water levels inside of them will always be the same that's because the pressure change in water only depends on the depth it doesn't depend on how wide or skinny the vessel is so that means the pressure at the bottom of a 30 foot straw would be the same pressure as the bottom of a 30 foot deep swimming pool but pascal's law of communicating vessels is only true if the liquid inside each of those vessels is the same density so one way we can try to defeat the greedy cup is to put a really dense liquid at the bottom so let's see what happens when we pour gallium in the bottom of the greedy cup all right so i have my liquid gallium here let's pour it in the bottom [Music] then pour the water on top we can get as greedy as we want we're completely over the fill line now but it doesn't leak out so you can see that when we start off with a much denser liquid in the greedy cup that is not able to do the siphon effect because the weight of the water on top of it isn't enough to push that dense liquid up so the gallium is only going to move up the u-shaped tube until it equals the weight of water outside of the tube and because gallium is so dense it's only a little tiny bit of gallium that moves up the tube that equals the weight of water above it but if you just use only gallium in the cup then the greedy cup should work as normal because it's the same liquid outside and inside and so it has enough weight to push it up and over and start the siphoning effect so we were able to defeat the greedy cup by putting a little bit of gallium at the bottom but what if we put it in a vacuum chamber can a siphon still work in a vacuum chamber let's try it out so let's fill it most of the way up let's turn on our vacuum pump okay now let's see what happens when i try to pour it hopefully this will work let's fill it past the fill line now [Music] it still worked so how is this siphoning right now even in a vacuum the amount of liquid that's above the surface of the water in that u-shaped tube is actually below the boiling point of water itself so it should cavitate and not complete the suction or the siphoning effect i'm guessing it's because the tube is small enough in there that the capillary effect actually plays a role and it can get sucked up even below the vapor pressure of the water and because we already have some flow it can just push those cavitated bubbles so basically it's not cavitating fast enough to break the siphon you can see that the water is degassing and even starting to boil but it was still able to siphon it out i showed in a previous video that suction can't work in a vacuum chamber for example if you try to use a syringe in a vacuum chamber it doesn't work so you can see that the greedy cup or pythagoras cup still works in a vacuum chamber pretty interesting so the vacuum chamber didn't work so what's the best way to overcome the greedy cup just hold the cup like this and thanks for watching another episode of the action lab i hope you enjoyed it if you did don't forget to hit the subscribe button if you haven't subscribed yet and also you can hit the bell so you can be notified when i release my latest video and thanks for watching and i'll see you next time

Channel: The Action Lab

Views: 2,397,728

Keywords: greedy cup, pythagoras cup history, Pythagoras cup, the action lab, gallium

Id: 1NTpXcp-pKM

Length: 6min 14sec (374 seconds)

Published: Wed Jul 14 2021