How To Make a Self-Starting Siphon

ding-dong Michael here today we're gonna talk about this a thing that you can make at home what does it do well take a look I have here a glass I'm gonna fill this glass with water that I've dyed blue so it's easier to see all the way up to the very top of the glass just like that perfect now watch what happens when I place this tube in the glass pretty cool right the water flows out and it keeps flowing out but how is this happening I mean I just put a tube in the glass the tube has no moving parts no pump what's pushing the water out of the glass well this isn't just a - no no it is a self-starting siphon I first learned about these from the Curiosity show and I am incredibly grateful because I mean they're a blast it's almost like magic but it's not magic it has everything to do with the shape of the tube and physics now to see how it works let's keep watching because it won't run forever eventually the flow will stop and that will happen when the water level in the glass is that the same height as the exit point of the straw the flow will get weaker and weaker as we approach that point eventually it'll just turn into a few drops and then it will stop and the system will be in equilibrium perfect at this point the forces acting on the fluid cancel each other out and the fluid stops moving but what are the forces well for a siphon like this the most relevant forces are weight forces every single molecule of water and air in this system is being squeezed by the weight of everything above it the lower down a molecule is the more stuff there is above it and therefore the larger weight weighs down on it so it's under greater pressure now because water and air can flow the result of this pressure isn't just a tendency to move down when possible oh no water and air molecules can slip by each other and so when under pressure they're ready to move in whatever direction they can think about an air molecule right here by the exit of the straw it is being squeezed by the weight of air above it against all the molecules below it and if that straw was suddenly evacuated of water and air you better believe that under pressure those molecules of air outside would rush inside all right so now that we're thinking about pressure let's look at a picture all right here is a diagram of what we have been looking at a container filled with water and a tube that is also filled with water the exit of the tube is at the same height as the liquid in the container and nothing is flowing why well let's take a look at the pressures at work first of all it's important to note that pressure depends on depth and that's really it I mean it also depends of course on acceleration into gravity and the density of the fluid that you're in but those don't really change much over these small distances it's the depth that matters not the volume of water just the depth so here at the entrance where is the entrance well the entrance is deep in the container and how deep well it's this distance deep and I'm gonna call this h1 perfect now before we get too far let's talk about some other depth that exists the entrance is also in much deeper water in the tube let's divide the tube in half and now I'm going to call this half the outside half and this half the inside half so there's a lot there's a lot more water the water goes up a lot higher here in the tube so what is this depth well from the surface of the water in the container down to the entrance this is also h1 all right same depth but the water goes up higher in the tube there's also this extra depth I'll call this h2 so h2 plus h1 equals the total depth on the inside of the tube over here on the outside how deep is the water at the exit well it is let's say h3 deep this is the distance from the top of the tube to the exit now let's talk about the pressures created here we've got a pressure proportional to H one that is coming from the water in the container and that's gonna cause water to go into the straw if possible but we also have a column of water h1 tall inside the straw that's creating a pressure in the opposite direction so they both cancel out let's not forget about air when it comes to canceling out by the way there's also air pressure right air pressure pushing on the water in the container and if this straw was empty that would that would cause the water to go into the straw but there's also air out here there's also air in contact with the exit and that air pressure is equal to this air pressure so they also cancel out all we're left with are h2 and h3 the depth of water above the water in the container on both the inside and the outside of the tube if h2 is equal to a ch3 that means we have the same pressure out of the straw into the container as we do out of the straw into the environment and so nothing will move however if I pour more water into the container and say raise the level of water in it up to here so this is now all water well now there is a greater pressure out of the container because h2 has become much smaller h2 is now only this large and if h2 is smaller than h3 if the depth of water on the inside above the containers level is smaller than the depth of water on the outside there's more pressure here moving out and so the water will flow out until the water level in the container has dropped back down to the same level as the exit at which point we'll be back at equilibrium there will be this situation h2 and h3 equal depths on the inside and the outside and the water will stop moving now let's see this in real life water will flow in the direction of the side of the siphon that has the deepest amount of water in it that isn't already under water right now those depths are equal so water isn't flowing but if I add some more water to the glass the water level in the glass will go up and the depth of the water in the siphon that isn't also under water will get smaller relative to the outside so the water will flow to the outside watch this it's regulating itself it's really beautiful this will continue until once again the water level in the glass is equal in height to the exit of the straw now let's say you don't already have a straw that's full of liquid how do you get to this point well there's a couple of ways to do that one way is to I kind of feel like this should finish it's just doing such a good job yeah hmm thank you all right so let's say your straw isn't already filled with liquid how do you get some siphon action going well let's fill this up to the brim that makes our job a lot easier because remember we only need the water on the outside of the siphon to go below the water level in the glass so the higher that level in the glass is the the less down we're gonna need the water to have gone to get the siphon to happen now if I put this empty straw in the glass not much will happen but I need the water level on the outside to get below the water level in the glass and I can do that by just like sucking on the straw like that perfect now it's working but let's say you want to siphon a liquid that you don't want in your mouth well there are a number of different options available to you all kinds of devices to draw the liquid through the siphon this is also a really fun thing to do with a straw cover one end of the straw and place it in the glass because you're covering one end the air won't be able to escape when you put it in so the air inside the straw will get compressed its pressure will be greater and it will push down on the water in the straw more so than atmospheric pressure does when you then release your finger the compressed air inside will escape and the water in the straw will rise up to the level of that it is in the glass however it won't stop there because while the water is being pushed up by pressure but what is pressure right it's force it's force per area so that force accelerates the water by the time the water reaches the level that it would normally stay at in equilibrium it still has velocity it's going to be slowing down but if I do this just right it won't slow down or get reversed until it's too late and the waters already passed over the bend and fallen down the other side below the water level in the glass let's see if I can do this I'm gonna use my thumb to cover the straw I'm gonna go in and when I release my thumb there you go the water is flowing out and nothing had to get in my mouth now that's pretty cool but what about this self working siphon how does it work because I don't even have to cover it over with my thumb where is my I found it so yeah how does a self-starting siphon work I don't need to use my finger or suck on it to get it started it just well true to its name is self starting well to see how this works let's go back to the overhead camera here's a cardboard model of the shape of our self starting siphon I'm gonna use this because this is kind of wet alright so what happens when I put the self starting siphon into a full glass of water well at first the siphon is full of air as it goes down into the glass the water in the glass enters the straw and pushes out the air but if I put this in really quickly through look what happens well there's enough pressure here for the water to get pushed all the way up to the top but that can't happen because of the bend and the straw so the water reaches this bend and it's still under pressure there's still a force acting on it so it continues to be accelerated but now it's going down oh so it's also being accelerated by gravity so it's velocity gets larger and larger and larger it turns that bend and it comes all the way up here once the water in the straw has reached this level it will not be accelerating up anymore however after all of this it may have reached we hope if I put the straw in fast enough a velocity sufficient to continue on around this third Bend before being stopped and reversed until it is low enough maybe like say here that it's below the water level in the container when that happens it will continue flowing and we've got ourselves a self started siphon to make your own self starting siphon you will need a full glass of water three bendy straws and some scissors now one of these straws will be our middle Bend and we're going to use it to ensure that one hump is higher than the other I'm going to do that by cutting the straw a bit shorter on one side of the bed that should be about enough perfect now as you can see we're going to be able to join the straws together to make an M shape where one side is higher than the other to join them I like to cut the straw at a bit of a diagonal like that so I get a nice sharp point in a gradual widening that way I can push them together let the plastic deform and they come together hopefully with a really nice airtight and watertight seal yeah is that good all right well the best way to check is to cover one end with your finger and suck on the other end if the feel is good then it should hold the vacuum I'm happy with that very good all right now let's join up the other side again I'm going to cut at a diagonal just like that and then I'm gonna push them together if you're having trouble with your seals you can always put some tape around the joint and that might be all you need to do but it's extremely important that they be air and water tight let's see how well I've done cover one end suck yeah see that that's good got a nice glue feel alright we're not quite done because I need to shorten one end I want the lower hump to be submerged in the water and right now the straws is a bit too long so when the higher hump is at the edge of the glass I think I'll need it to be maybe I don't know that short to be safe let's make sure it's gonna fit in the glass and let's make sure the seal is still good okay all right I think we're ready I think we're ready to test our homemade self-starting siphon in three two one Hey look at that how cool I love making these things so please make some at home and play around with pressure and what pressure can do it is a blast for more hands-on science check out our curiosity box stay safe out there stay dry and as always thanks for watching [Music]

Channel: D!NG

Views: 1,252,221

Rating: 4.9648366 out of 5

Keywords: vsauce, michael stevens, siphon, science, diy, at home science, learning, homeschool, physics, learn at home, science project, water pressure, air pressure

Id: 1vq_h4myH1E

Length: 13min 23sec (803 seconds)

Published: Thu Apr 09 2020

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