You can try it with larger flow areas where surface tension effects will be less prominent to confirm whether it is related to surface tension. Cool video!
Practical Engineering Good call Grady. I'd be interested in seeing a side by side setup with gradually increasing cross-sectional areas, kind of like a pan flute. Edit: Also, some different viscosity liquids would be neat.
I’ve been thinking about this more and it really has me interested. Water falling from the faucet should be supercritical flow meaning the flow velocity is faster than the wave celerity. So there should be no way to affect the flow upstream with an obstruction. Maybe surface tension travels faster than waves? This is beyond my knowledge of fluids, but a really cool phenomenon.
There are two different wave speeds to worry about. There's the speed of the surface waves, but also the much faster speed of the sound waves within the fluid. It's the sound waves that transfer most of the energy and momentum. (Like, consider the bow shock of a boat. Even when the boat's traveling faster than the surface waves, which they often do, you still get a bulge in front of the bow of the boat.) But yeah, I agree that it's probably not just a surface tension effect for this reason.
To me, it just looks like the water it stacking up on itself because it’s incompressible. The flow rate wants to stay the same and the water wants to stay together, so it ripples up to create a longer path.
Wouldn't it be just that the water is slowing at the point of intersection and the ripples are pushed back up the stream? Blow air through your lips and see if you feel the wind on your chin. You introduce and obstacle slowly. Do you start to feel wind on your chin?
To my knowledge, surface tension is the speed of sound. If you had a rod all the way up to the moon, and you move the bit near earth the tip near the moon would not move faster then the speed of light.
I'd imagine it's from the particles/atoms impacting stuff, causing them to bounce back (on an atomic level, on a large scale they just flow to the side) and when they bounce back it sends energy backwards as a wave. Having a constant and mass amount of atoms hitting it like this and reflecting their kinetic energy, probably is whats causing the wave. If you increase the rate of flow by pressurizing it instead of relying on gravity, and I'm right, the wavelength should get shorter. It'd make sense that when you move your finger towards the faucet the length of the visibly wavy area increases as that's getting closer to a source where the energy can get reflected back, ant at some specific length (which you'd calculate using gravity and the mass of water maybe and such) it becomes resonant and most visible/strong, or tuned to the frequency if resonant isn't the right word, like selecting the correct/optimal antenna length for a wavelength where the waves are reflected at the exact right point and none of them cancel each other out. Calculate the "antenna length" for molecules of that weight traveling at that speed (you'd have to know the length to get the speed), and see if it creates the most stable wave even at each octave. I'd consider that reason to call it the cause instead of surface tension (though surface tension is required to get a wave instead of spatter all over the place)
Hi Steve. You should try this with something that has been coated with a hydrophobic substance. It would be interesting to see if the loss of adhesion to the obstruction would change the effect.
Or he could just use different shapes to vary the anti-node. That would hopefully set him on a path to building a relationship between boundary conditions and wave propagation. You could build a law that way.
Steve it's really refreshing to see how you can find such cool phenomena in ordinary things! Your videos always show the power of science to describe our world, keep up the good work
Reminds me of Feynman. He famously made one of his largest discoveries trying to figure out (if my memory doesnt fail me) why a medalion on a wobbling tray is wobbling with a different frequency than the tray itself.
Oh I hadn't heard of that, really cool. It just shows how looking at the world with a different, curious perspective can help us answer big questions we didn't even know we needed to be asking.
I remember wondering about this when I was a child. Then I grew up and got dull. Thanks the internet we can enjoy people like him who still kept in touch with his inner curiosity.
So often I come on this channel and the video is something I've wondered about since I was a kid, and it sort of validated that I wasn't asking stupid or pointless questions but that my parents were just too worn down to deal with them all
I think you're right. These standing waves also explain why the wavelength seems to shorten downstream. The water downstream has been accelerating under gravity for longer so is moving faster, and conservation of mass means the stream has to get thinner (you can see that in the video). This also means that there is less mass per unit length in the stream, and just like with a guitar string, less mass per unit length (a thinner sting/stream) means a higher pitch note with a shorter wavelength. So the natural wavelength of the standing wave smoothly decreases from top to bottom as the width of the stream smoothly decreases.
But what about the vertical offset difference visible on the video that happens between these two kinds of waves? The droplet creating wave has the pinch and bulge points perfectly aligned vertically, if you look at the "left and right side" of that stream. On the other hand, the waves that appear when you put an obstruction in the stream are, what seems like vertically offset, almost snaking, if that's even a word, or maybe even helixing. What I mean is, we didn't see the tridimensionality of the stream in the video, I don't quite understand why the water would make these snaking vertically offset waves given that it would cause more stress on the surface tension, so I think that the stream actually forms a helix. I hope someone understands what I'm trying to say.
I also considered the 3rd dimension aspect of it but it may not be screwy. I figure the target provides an obstruction transmitting a decelerating force up through the column of water and that probably needs a deflection in one polarity from the center and some unclear dynamic between flow and surface tension backpropagates the transversal wave in a single plane. But it's possible there is some spiraling, if the unknown dynamic allows such a standing wave configuration. One premise I like to adhere to is that if you can setup an honest simulation in a computer that produces the observed effect then you might well have explained it adequately. I suspect it would be very difficult to replicate this in a model. I'm guessing the speed of sound in both water and air are in play. While water play might seem frivolous, such a concept of a seemingly static standing wave through flow might turn out to be all important in some forward part of physics.
I think you're right about the wavelength. I also wonder if it's a helix. Might it be related to this effect in high viscosity fluids? ua-cam.com/video/zz5lGkDdk78/v-deo.html
Completely left field, but this made me wonder what properties water falling at terminal velocity would have. Wonder if that would impact this experiment....also, can water travel at terminal velocity and maintain laminar flow?
So I'm curious did your parents say this was fascinating which launched you into a physics career or did they just tell you to stop playing with the water which crushed all your scientific curiosity and now you are trying to find yourself? 🙂 Noticing this at the age of 5 is impressive!
Me too! I'm 54 years if age and have been wondering about this since I was a child. Thank you Steve for shedding light on this and helping me understand. Washing up has become interesting, (for a while)!
If you look carefully, the bubbles arr not aligned. Maybe the effect has more to do with viscous fluid coiling (like honey coiling) since water has some viscosity
Disappointed that you poured the water from a funnel, not a beaker ;) How would this work with different fluids with different surface tension? Would it be hard to get a laminar flow?
I'd guess that it's a scalable effect, i.e. that higher or lower tension will require wider or narrower flow to work, but I'm not sure what way round that would be! I'd guess higher tension would be able to cope with greater flow (as it can do more pulling) so presumably lower tension could work for even finer streams. Viscosity should also play a role, I think. :)
Dragon Curve Enthusiast I agree, but since surface area is proportional to radius squared and volume to radius cubed, I suspect the effect would be greater for narrower streams, so lowering surface tension and having a finer flow MAY lead to the same outcome.
Could you try to capture it in slow motion so we can see how the "standing wave" forms? Does it go upwards? Does it appears in the whole stream at the same time? Is is instantaneous or a "slow" process? I think it would be very interesting to see :)
Thinnestmeteor it will form from down to up, because information travels through materials at the speed of sound in that medium. So the upper part of the stream won't notice instantaneously that an object has been placed under the stream.
Anything with viscous fluids is simulated using Navier Stokes. There are many simulation schemes that use it, but surface tension is an additional effect that needs to be added into the momentum equation (the second of the three). I really want to explore this on my free time, but right now I’m having to focus on my plasma research
I'm glad you mentioned standing waves in application to guitar strings! I'm wondering if you would investigate laminar flow in wind instruments, and how air stream might interact with the standing waves within a column of air
I loved how you provoke reactions with your scene 3:20 that plays with the suggestion evoking a life familiar scene, like when we piss the wall when we were kids.... and then right next silently you gives us that look of " Is not what you are thinking" Ha ha ha ha ha is so magnificently well executed!
I've wondered this for years, but always thought it had to do with the rope coil effect, especially because when you obstruct the stream really close to the source you can almost see a steady twist in it. I would love to hear your thoughts on this theory!
I smoked for about 15 years, but happily quit smoking about 12 years ago. Your candle smoke reminded me of something I saw quite a lot when I still smoked. The column of smoke from a cigarette would sometimes create what appeared similar to laminar flow... sometimes there would appear a kind of ripple in the smoke column and interrupting it would cause the wavelength of the ripples to change. I still don't know why, but think this video might be part of that answer.
5:00 Okay it took me a while but I finally understamd why the curved has less *surface area* than the cylinder formed by the loops. The *perimeter* of the middle part gets smaller, so it has less surface than the full cylinder.
I can't believe how relevant this video is to me. When I saw the thumbnail I audibly gasped and debated whether to click it. You see I noticed this phenomenon years ago and was fascinated by it. On my last day of grade 8 I talked to my science teacher about it and he didn't know how it worked, telling me to investigate it further and maybe do a more organized study on it in the future. I couldn't get further with my knowledge, so I didn't investigate it, but I remained fascinated, occasionally turning the water on the tap in my bathroom down very low and trying it out when washing my hands. A few years later I did a science project in high school on Chladni plates, in which I researched standing waves and actually ended up having a friend who made a working Chladni plate for an in-class demonstration which I still have. And now I sit at a desk looking through UA-cam and I see this video. When you talked about forcing a node at a specific spot and having a standing wave formation, I sat for a few moments with my mouth gaped open. I can't thank you enough for making this video.
Geez, it was just this last couple of days that I figured out why some bathrooms have higher than average urinals and now I know the name for that bit of science - Rayleigh Plateau Instability.
I've spent plenty of time playing with the laminar flow in the sink and have had these questions run through my head without any answers, so thank you for explaining 30 years of curiosity.
40 seconds in I realize that that's due to water's viscosity, like pouring honey over toast Edit: And because it's laminar flow, the waves formed are non-chaotic static waves
It's surface tension. When you block the flow, it backs up the stream and it buckles. When the droplet separates from the stream, it snaps the end of the stream closed and the stream acts like a rubberband that sends energy upwards which has the effect of a momentary blockage.
55Ramius The adhesion of the water to the to an object forces the cohesive properties of water to bend in the most efficient and stable way. Where stable conformations exist, you get standing waves. Liquids with less surface tension have less surface tension because of a decrease in cohesive properties. This means fewer stable conformations resulting in fewer standing waves, particularly when the distance between adhesive endpoints (the faucet and the bowl) decreases. Mix a few drops of dish soup into water and try it out.
Steve Mould, this is one of the bloody greatest channels on the internet. You do a great job of explaining and visualising phenomenons and catching my interest. I really enjoyed this video, as I did so many of yours before. Keep up the great work! This is stuff I wish I was presented with in science classes!
Over 20 years ago, I tried to do an A-level Physics project looking at these standing waves. I didn't get very far with it, though and ended up switching to looking at how pendulums made from springs behave. I've always wondered about this, though, so thank you for investigating it.
Thats just what i tough. Flow is obstructed with finger, water molecules hit the finger, slow down and need to go around longer way, but another molecules are already hitting them and slowing down again, but there are molecules above them that have greater speed so water is piling up? I also think that this bending is in fact a spiral shaped stream, because curvature on the left doesn't cover curvature on the right side of stream or thats just the point of view.
I just checked with my own tap, and it's definitely a spiral. I don't know what that means for the different theories of why the water bends, but it did bother me that the shape with an obstruction didn't exactly match the shape that causes the breaking into droplets. If this does have something to do with Rayleigh-Plateau instability, then something has to explain the spiral shape. It's still a standing wave, just with one component that's out of phase with the other. And, notably, a spiral should be unable to cause drops of water to break off. The "piling up" hypothesis seems to fit what I'm seeing. All the outermost water is pushed outward, but its hydrogen bonds pull it back inward at the same time. Along with some small random motion to the side, this could cause orbits to form, closely followed by the orbiting water tending to favor whichever orbit happens to be densest, again because of the hydrogen bonds. A lot like the formation of planets from orbiting dust clouds. And since the water is falling while orbiting, it traces out a spiral. I wonder if a high-speed camera would show anything useful. If the water does pile up and start orbiting, I'd expect to see the spiral grow upward over time.
Using high fps camera would be nice. I wonder how long can be the stream to actually form the spiral from obstruction point to source and how fast its growing upwards. Would it be the speed at which the water falls down, faster/slower. Maybe the "frequency" of the ripples as shown in this video depends on the speed of water hitting the obstruction point, the further it is - greater speed caused by gravitation - denser the spiral. I wonder also if the direction of the spiral is always the same, and if its the same as water that you let go through a sink hole.
Could you explain the change in wavelength of the ripples as the obstruction moves further from the source? My initial thought was that the coiling radius might have been related to the velocity of water (an obstruction further from the source blocks faster-moving water, and somehow this translates to tighter coiling). However, this paper (tel.archives-ouvertes.fr/tel-00156591/document, p.24) and my own brief experimentation seems to show the correlation isn't linear. The standing wave hypothesis could explain the change in wavelength, but you would expect the change to be sinusoidal, not linear. Perhaps a tap just doesn't show a large enough sample size?
I think the reason for the tighter coiling is that the column of water, and therefore the spiral around it, is thinner. Thinking again in terms of orbital mechanics, orbiting closer to the center causes the water to orbit faster, which means it doesn't fall as far before coiling all the way around. Also, since there's less water in a slice of a thinner water column, it's less resistant to changing its direction. Of course, faster-falling water would tend to lengthen the coils, but it looks like, at least at the heights we've tested, thinness wins out. I'm no expert on fluid dynamics or orbital mechanics, so I might be wrong about a lot of this. In particular, before looking at that paper, I hadn't thought of considering the water to be like a rope. In that case, the explanation is probably more complex than the orbiting model would suggest. And I'm not really sure how to test what I've proposed.
I think you're on the right track. I think the missing piece of the puzzle is the disruption of acceleration. The column of water in free fall will get thinner and thinner as it falls and accelerates until it eventually breaks into droplets. So you're stopping the flow and forcing a rapid deceleration of the water at the end, forcing the node as you put it. The first node creates a deceleration of the water behind it, and subsequent nodes form. To prove this you could use slow motion footage and if I'm right the nodes will appear one after the other starting from the bottom. The waves get smaller as you go down the column of water because you're allowing the water to reach a greater speed before interrupting it.
I also think so. And if you look closely the the "waves" are shifted from the left to the right side of the stream unlike with the droplets. In 3d it would form a spiral, just like if you pour honey for example (just a smaller spiral).
Ricci flow, Poincare, Perelman, Bose- Einstein condensate all similar to what you research. J,P,Yodd God's finger pinch holes. Like does straw has 1 or 2 holes. Hollow grammic materialization of BE glue into 26 different mass particles. Hole in a hole in a hole. E🎱 math, primes, Riemann... all is connected. I love all your work. Learning is more fun the way you do things. Thanks!
This was very intriguing. If more videos were exploration rather then having an actual answer, I would enjoy that far more then getting an answer. It actually convinced me to get up and go to my sink and start experimenting. Sadly, my sink is not giving me a water flow like yours so I have bad results, but I plan to gather some materials to go farther. Awesome video!
I used to turn the tap down to the thinnest laminar flow stream and then slowly push my finger up the stream in order to push the waves up until they touched where the water emerged and then that would trigger the Rayleigh-Plateau instability and then the water flow would remain broken without changing the flow rate (opening the tap further). I tried the reverse and could sometimes get it to shift state back to laminar again. I didn't know any of the physics was behind it so thanks for diving deeper for us!
So my thinking is: Since you put something in the way of the flow, the molecules get slowed down(maybe even get pushed back a little bit. So the molekules in the front of the flow get slowed/pushed back, but there are more molekules coming at unchanged speed from behind, so the molecules bottle up and need to go somewhere and form the bulge. If you look closely at 1:17-1:45 you can see, that if you hold the object in the middle of the stream, the bulges are shiftet (when there is a bulge on the right side, there is a pinch point on the other side and vice versa), because the one side is obstructed while the other can just flow normally. And if you hold the object directly under the stream you have the bulges lined up (1:36), since you obstruct the flow on both sides equally. In a confined space (a tube or a channel), if you put an obstruction somewhere, it would create turbulences, since the bottled up molecules cant go anywhere and swirl up. In an open stream however they can just form these bulges because there is nothing in the way. Can someone debate?
That is not the explanation I thought of, because the ripples become bigger as you get closer. So I figured it must be dependant on the force with which it hits the obstruction. And that increases with the height it's been falling from. If you move your finger against the stream it also makes the ripples bigger (though I'm unsure, you guys need to check) Maybe the tighter ripples are higher energy because they're a higher wavelength ? Or is it bigger ripples that have more energy ?
Great video! When I was a kid I was able to watch and play with this for hours. After watching I have the feeling that velocity has a crucial part at this phenomenon as well. As the water moves down it's velocity increases, so the stream is constantly stretching, so this is the reason it gets thinner and thinner on the way. Wherever it hits the object, the flow slows down, so it gets thicker before the touching point. Whenever the object is closer to the source, the stream thickens, whenever it is farther it grows thin. I assume when it gets thinner it gets more unstable, and after a certain length it breaks into droplets. Maybe because it reaches the speed it can not be laminar anymore, and the occurring turbulence breaks the stream up. When it's short, I also think about the stream as a water in a thin flexible and elastic pipe, wherever it's diameter shrinks I assume the momentum of the flow will produce extra pressure on the upward wall of the thin bridge, while the quick deceleration at reaching the object creates an extra pressure on the downward wall of the thin bridge. While at the object it looks like when two separate water bodies are just touching each other. I just wonder why the pattern shows up only at the end of the stream, and why it dies after a several ripples?
I love that I wasn't the only one wondering... now explain to me why a slow stream of running water flowing down a flat plate of glass so closely matches the motions/meanderings of a flowing river. Cheers!
I know this video is two years old now but I can't help but notice that the standing waves seem to spiral clockwise from top to bottom. I'd love for you to revisit this as I feel there is more going on? Excellent work btw 👌
As I've seen a couple of other people mention below, it looks like it also has to do with the viscosity of the fluid. When something is put in the way of the stream, the fluid nearest the obstruction can't get out of the way as quickly as more fluid is coming down, so it causes the stream to bulge where fluid is piling up. But that piling up also increases the pressure (due to surface tension preventing further bulging) and that increased pressure increases flow which reduces bulge. You end up with a series of bulges and pinches in a pattern that balances these two flow rates.
If the phenomenon you mentioned was related to this one, you would see the flow become thinner and thicker symmetrically. In this case it doesn't look like the stream is stretching, but rather crumpling (like soft serve ice cream). The diameter remains even, and doesn't bulge along the generated spiral. I think you were on the right track when you described the layers of laminar flow. On the outside, you have a slower-moving layer of surface-tensioned water, almost like a stretchy rubber hose. When you interrupt the stream, this water piles up on itself, but because the surface tension won't let that outer layer shatter, it keeps the inner layers flowing laminarly in a crumpled path (again, like a thin rubber hose) until it interacts with the interrupting surface. The phenomenon becomes tighter lower down because the water is moving faster, and there is more force being applied to the outer, springy surface-tension layer, causing it to compress more tightly. I imagine the fact that the cross-section is smaller lower down also means that the water can pass the obstruction easier, which lessens the l length of the pile-up further.
I have always been fascinated by these ripples. I imagined the ripples as energy reflections going back up the stream after hitting my finger. The water molecules are speeding down and hit my finger and they get reflected back up, but they run into more water that is moving down, so it makes a chain reaction moving upwards but loosing some energy as it goes up into the oncoming stream, that's why the ripples get larger as they go up.
My hypothesis on the "standing wave" is that when the flow touches an object, the water at that point drops its speed due to the adhesive property of water. So, due to this "touching" and "slowing down" the water above it somehow... bounces back up because of this "water collision" (?). Sorry if my explanation is too complicated, but it's sorta like people in a line- assuming they're all walking, when the person in front suddenly stops or slows down, the person behind collides and sorta "bounces off" of the person in front... And this is what's happening in that flow of water; that's also why the farther the object is from the start of the flow, the less "collision bumps" there are. That's just my hypothesis though ^-^
Your wonderment of the world around you is inspiring and contagious. I love how all your videos show that you needn’t have a huge lab to observe and participate in science. Thank you
I noticed this effect literally half a century as a kid playing around with the faucet. I'm not sure I understood the full context of your explanation re: pressures, but I intuitively buy the standing wave theory. It does seem to have that sense about it.
Love your videos, Steve. So glad you never grew up and became ‘sensible’! This laminar flow video which I have only just discovered reminded of another conundrum; when bubbles rise in my aquarium they do not go straight up! The bubbles seem to spiral up on a helical path that may be related to the size of the bubble. I wondered where the lateral force that wobbles the bubble from side to side comes from?
I'm really fascinated by the image at 5:52. The water stream is doesn't interact with the glass right underneath it, but is actually "sucked" onto the glass to it's side. I would assume this is also due to the high surface tension properties of water, but it's really interesting to see!
2:24 Cool thing about candles - the "smoke" that you see when you blow out a candle is vaporized wax. You can demonstrate this by blowing out a candle and then touching a flame to the stream. It will light, travel down the stream, and relight the candle.
Here is something I encountered a long ago: Get yourself a length (about 1 metre) of a hose with wavy wall (similar to these waves). Rotate that hose above your head (that causes air to be pulled through the hose via centrifugal force) or simply blow into the hose. The hose will start to "sing" (emit a tone). If you rotate it faster (or use a blower that produces high speed air stream), the tone suddenly jumps to a higher tone (maybe the original is a base frequency and the higher one is a multiple of this base frequency?). On the other hand a hose with a flat (non-wavy) wall does not sing at any speed of flow through it.
I liked watching this. Two things: - 1. At about 00:39 we see the water curve around the finger. This shows the Coanda effect, which I remember reading about in Scientific American way back in the issue of June 1966 (thanks Google) and have never forgotten. 2. I think there is a contribution of pressure change at both when a drop separates and when the flow meets an obstruction that generates a reflected pressure wave back up the stream. Backwards propagation of a pressure wave is well-known. That is why sometimes you have to brake suddenly on the motorway, then speed up to find no visible reason why people ahead were braking. I realise drop separation in a simple downwards flow and encountering an obstruction are different, but still think pressure reflection is common to both. No, three things! As I understand it, water is both one of the simplest molecules, yet still not fully understood after all these years of Chemistry and Physics. It seems we are still at the observational stage, as per this post, since computer modelling remains both varied and not resolved at the moment. As an atheist, I think water competes with the Sun as something worthy of some kind of worship :-)
I was 10 years old ... Without a cell phone or other things to do while you are at the toilet, it happens that you experiment. I realized that if I took my finger in the water from the tap in front of me, With a small amount of water flowing, it became this phenomenon. From that time until now I have thought about it without spending too much effort. Suddenly this explanation came up. Thanks
Hey Steve, i have also noticed that if reduce the flow rate of the stream until it's just at the brink of starting to break off but is still laminar, it'll remain laminar until you bring in an obstruction after which it will not go back to its state of laminar flow even if the obstruction is removed. And this phenomenon is more likely to occur if the obstruction is closer to the source of the stream. To get back to laminar flow, you have to stop the stream altogether and reset it.
Steve's videos are the explanations of the things that I found out in my everyday life. I used to turn on the tap very slowly in my bathroom, adjust the flow rate until I got the perfect ripple, and then stare at it. Often this would keep me staying inside the bathroom for an hour or two, my mother would knock on the door at a regular interval of 5 minutes. Often she screamed, "It has been so long, what the hell are you doing? GET OUT NOW!" 😂😂
On the top of a shower head, its droplets are near each other. As they accelerate downwards, they begin to separate due to gravity. Furthermore, there is an attraction between water molecules (responsible for the surface tension), which keeps the molecules in chunks, so a chain of spheres with different velocities makes this pattern. At 3:11 and 6:33 is visible that the bottom chunks are slightly wider than those on the top because they accelerated more. The big one below became so far apart that it is just about to split off. Surprisingly, at 3:16 and 5:54 the pattern is inverted, the wider ones are on the top. But is noticeable that a tilt appears; the line is bent (at 3:16) and there is a twist (at 5:54): so there is an attraction. Thus, this phenomena becomes very complex.
Another cool water faucet phenomenon I notice is when filling a container (or cup) of water. When the waterline gets close to the top of the stream, it turns from a cylinder to a cone flare at the bottom. It's like the force of the water pushing up against the stream evenly distributes across the edges, causing the sides to form a cone.
Always enjoy your videos. You actually take the time to experiment and test all the things I see as a passing curiousity. Keep doing what you're doing!
I'm already a subscriber of your channel and hadn't watched this video of yours. But recently when I was walking down a slope and water was flowing down slowly. I stopped to observe and it had these very small ripples in front of the waves. When I was searching about that I stumbled upon this awesome video of yours. You explain it really well and it has quite a lot of parallels to my question. Thank you Steve!
Really interesting video. I think the reason the ripples get more "squashed up" when you move the obstruction further down the flow is due to a doppler-like effect. The waves propagate upwards from the obstruction at some wave speed, relative to the speed of the water. When the flow is slow (i.e. nearer the tap) the wave speed is much greater than the flow speed and the wavelength we observe is hence longer. As we move down to where the flow is faster (because the water has been falling a longer time) the flow speed become close to the wave speed and so the wave fronts are closer together, giving a shorter wavelength. If you went further down, to where the flow speed was actually greater than the wave speed (torrential flow), this effect wouldn't happen.
And I discovered (probably some people have done it too) that if you get closer to the source it starts to go drop by drop then you can stop to stop the water flow and it will keep going drop by drop a few seconds and they go back in stream. Also you can open the tap a very very tinny bit and you'll see that the stream stop at some point and it becomes individual droplets. There must be some conection going there.
Hey steve, see the small patch on front of the bubble at 5:13 where the light is reflecting and refracting? I have found this interesting and beautiful for a long time. It would be awesome if you did a video on this. What I have observed is if you just have a flat vertical bubble film in a bubble wand you can observe the Colors filtering from bottom to top. First is multiple bands of teal and Pink then bands in this order: green, pink, yellow, green, blue, purple, pink, orange, yellow, light blue, dark blue, dark purple, orange-ish brown, white, silver then clear then it pops; seems to always happen in this order. The best way to see vibrant colors is hold the film so it is reflecting a bright light. If you blow slightly on the bubble film the colors swirl and look kinda like a kaleidoscope.
Something I just noticed in this video is that the reflection in the back at 5:13 is yellow-green and purple this must be from passing through a second layer of bubble on the way to the camera. So now I'm wondering how many layers you could line up and how many times the color will change or maybe end up repeating. I think the reason this happens is that gravity is pulling the small amount of water trapped between the two layers of surface tension and getting slightly thicker towards the bottom. I think the different thicknesses reflect/refract different wave lengths of light, probably even be IR/UV light being reflected from the clear part that we can't see.
It could be for the same reason that honey curls on a surface and the amount it coils after pouring changes with different viscosity. Maybe this is the water attempting to coil but due to its low viscosity it simple appears as ripples.
Very interesting. Though I feel something is missing here. You talk about the Reyleigh-Plateau instability, and how it splits the stream in chunks, due to surface tension. But I feel there is an other actor on the scene: fluid viscosity. Somehow it helps surface tension kind of pull on the liquid to keep it together, and somehow it also prevents chunks from splitting. There was a video this or previous week on Smarter Every Day where Destin explains a phenomenon that I find really similar: honey coiling when you pour it in thin laminar flows. His explanation is more centered around fluid viscosity and how it pushes the stream around to produce these coils. I can't help but think this coiling phenomenon and those standing waves in water that you show are somehow related.
You can try it with larger flow areas where surface tension effects will be less prominent to confirm whether it is related to surface tension. Cool video!
Practical Engineering Hey! It's you!
I think it is difficult to avoid turbulence while increasing the stream diameter.
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My thoughts exactly. (Actually, I assumed it was gremlins or possibly aliens (perhaps alien gremlins? hmm.). You should listen to the engineer.)
Practical Engineering Good call Grady. I'd be interested in seeing a side by side setup with gradually increasing cross-sectional areas, kind of like a pan flute.
Edit: Also, some different viscosity liquids would be neat.
I’ve been thinking about this more and it really has me interested. Water falling from the faucet should be supercritical flow meaning the flow velocity is faster than the wave celerity. So there should be no way to affect the flow upstream with an obstruction. Maybe surface tension travels faster than waves? This is beyond my knowledge of fluids, but a really cool phenomenon.
There are two different wave speeds to worry about. There's the speed of the surface waves, but also the much faster speed of the sound waves within the fluid. It's the sound waves that transfer most of the energy and momentum. (Like, consider the bow shock of a boat. Even when the boat's traveling faster than the surface waves, which they often do, you still get a bulge in front of the bow of the boat.)
But yeah, I agree that it's probably not just a surface tension effect for this reason.
To me, it just looks like the water it stacking up on itself because it’s incompressible. The flow rate wants to stay the same and the water wants to stay together, so it ripples up to create a longer path.
Wouldn't it be just that the water is slowing at the point of intersection and the ripples are pushed back up the stream? Blow air through your lips and see if you feel the wind on your chin. You introduce and obstacle slowly. Do you start to feel wind on your chin?
To my knowledge, surface tension is the speed of sound. If you had a rod all the way up to the moon, and you move the bit near earth the tip near the moon would not move faster then the speed of light.
I'd imagine it's from the particles/atoms impacting stuff, causing them to bounce back (on an atomic level, on a large scale they just flow to the side) and when they bounce back it sends energy backwards as a wave. Having a constant and mass amount of atoms hitting it like this and reflecting their kinetic energy, probably is whats causing the wave. If you increase the rate of flow by pressurizing it instead of relying on gravity, and I'm right, the wavelength should get shorter. It'd make sense that when you move your finger towards the faucet the length of the visibly wavy area increases as that's getting closer to a source where the energy can get reflected back, ant at some specific length (which you'd calculate using gravity and the mass of water maybe and such) it becomes resonant and most visible/strong, or tuned to the frequency if resonant isn't the right word, like selecting the correct/optimal antenna length for a wavelength where the waves are reflected at the exact right point and none of them cancel each other out. Calculate the "antenna length" for molecules of that weight traveling at that speed (you'd have to know the length to get the speed), and see if it creates the most stable wave even at each octave. I'd consider that reason to call it the cause instead of surface tension (though surface tension is required to get a wave instead of spatter all over the place)
#TeamLaminarFlow
How do you only have 7 likes??
still
Don't let Veritasium see this...
I love you videos, sir! thank you for your consistent effort!!
Turbulent! Turbulent! Team Turbulent!
Hi Steve. You should try this with something that has been coated with a hydrophobic substance. It would be interesting to see if the loss of adhesion to the obstruction would change the effect.
Or he could just use different shapes to vary the anti-node. That would hopefully set him on a path to building a relationship between boundary conditions and wave propagation. You could build a law that way.
^ this
He should also try to distillate it with exo-ionic sub atomic particles, to increase the kessleration.
L'effetto coanda si verifica con qualsiasi fluido , anche con l'aria
3:30 - "No, I'm not pissing on the wall"
Hahahaha that face cracked me up xD
It was a definite "what am I doing with my life" face. I could relate.
I bet that is what sparked the idea.
JustKeith I dunno. Can't say I've ever managed laminar flow from my pee-pee. Not that I've really tried though.
Every guy watching this knew what he meant though!
"Steve - did you finish the washing up?"
"Ahhh, ... well, here's an interesting thing..."
Steve it's really refreshing to see how you can find such cool phenomena in ordinary things! Your videos always show the power of science to describe our world, keep up the good work
Reminds me of Feynman. He famously made one of his largest discoveries trying to figure out (if my memory doesnt fail me) why a medalion on a wobbling tray is wobbling with a different frequency than the tray itself.
Oh I hadn't heard of that, really cool. It just shows how looking at the world with a different, curious perspective can help us answer big questions we didn't even know we needed to be asking.
I remember wondering about this when I was a child. Then I grew up and got dull. Thanks the internet we can enjoy people like him who still kept in touch with his inner curiosity.
so... pee closer to the wall. got it
Not all the time, only when your stream is stable and steady or else you're going to give yourself a golden sprinkle.
that part was amazingly funny.. as he wanted to make sure nobody has any strange ideas about where that liquid comes from! :)))
urinals are usually where I make my deposits, their walls and those of bowls have a curve, I utilise that to avoid splashback: pee along the curve
@@frankzaffuto3670 Same. Gotta utilize that curve to avoid splash back. So important. 👍
@@swoop_cheetah Love the kinda scientific discussions that go on in these comments.
So often I come on this channel and the video is something I've wondered about since I was a kid, and it sort of validated that I wasn't asking stupid or pointless questions but that my parents were just too worn down to deal with them all
I think you're right. These standing waves also explain why the wavelength seems to shorten downstream. The water downstream has been accelerating under gravity for longer so is moving faster, and conservation of mass means the stream has to get thinner (you can see that in the video). This also means that there is less mass per unit length in the stream, and just like with a guitar string, less mass per unit length (a thinner sting/stream) means a higher pitch note with a shorter wavelength. So the natural wavelength of the standing wave smoothly decreases from top to bottom as the width of the stream smoothly decreases.
But what about the vertical offset difference visible on the video that happens between these two kinds of waves?
The droplet creating wave has the pinch and bulge points perfectly aligned vertically, if you look at the "left and right side" of that stream.
On the other hand, the waves that appear when you put an obstruction in the stream are, what seems like vertically offset, almost snaking, if that's even a word, or maybe even helixing.
What I mean is, we didn't see the tridimensionality of the stream in the video, I don't quite understand why the water would make these snaking vertically offset waves given that it would cause more stress on the surface tension, so I think that the stream actually forms a helix.
I hope someone understands what I'm trying to say.
I also considered the 3rd dimension aspect of it but it may not be screwy. I figure the target provides an obstruction transmitting a decelerating force up through the column of water and that probably needs a deflection in one polarity from the center and some unclear dynamic between flow and surface tension backpropagates the transversal wave in a single plane. But it's possible there is some spiraling, if the unknown dynamic allows such a standing wave configuration.
One premise I like to adhere to is that if you can setup an honest simulation in a computer that produces the observed effect then you might well have explained it adequately. I suspect it would be very difficult to replicate this in a model. I'm guessing the speed of sound in both water and air are in play.
While water play might seem frivolous, such a concept of a seemingly static standing wave through flow might turn out to be all important in some forward part of physics.
I think you're right about the wavelength.
I also wonder if it's a helix. Might it be related to this effect in high viscosity fluids? ua-cam.com/video/zz5lGkDdk78/v-deo.html
Completely left field, but this made me wonder what properties water falling at terminal velocity would have. Wonder if that would impact this experiment....also, can water travel at terminal velocity and maintain laminar flow?
Dude! I noticed this when I was like 5 and I’ve been wondering why this happens ever since! I’m 23 so a long time lol
So I'm curious did your parents say this was fascinating which launched you into a physics career or did they just tell you to stop playing with the water which crushed all your scientific curiosity and now you are trying to find yourself? 🙂 Noticing this at the age of 5 is impressive!
I spent ages as a kid at the bathroom sink experimenting with this !!! 😂
Me too!
I'm 54 years if age and have been wondering about this since I was a child.
Thank you Steve for shedding light on this and helping me understand.
Washing up has become interesting, (for a while)!
I remember being fascinated about this as a kid and playing around with it enough to get yelled at for wasting water
If you look carefully, the bubbles arr not aligned. Maybe the effect has more to do with viscous fluid coiling (like honey coiling) since water has some viscosity
Muzkaw That's what exactly what I was/am thinking! Would be interesting to see the effect with different fluids...
That was exactly what I thought of.
Philipp Reiger Oops, I messed up that sentence, please forgive me.
Agreed, that’s what it reminded me of.
Keksdieb I didn‘t correct you, it was really like that. 😂
Your videos deserve way more views, my friend. Incredible how you pull up such new stuff from regular daily life. Love your work
Thank you!
You might say that this specific field of study is... untapped.
I'll see myself out.
Disappointed that you poured the water from a funnel, not a beaker ;)
How would this work with different fluids with different surface tension? Would it be hard to get a laminar flow?
Yes! Use soapy water and see whether you get the same effect!
I'd guess that it's a scalable effect, i.e. that higher or lower tension will require wider or narrower flow to work, but I'm not sure what way round that would be! I'd guess higher tension would be able to cope with greater flow (as it can do more pulling) so presumably lower tension could work for even finer streams.
Viscosity should also play a role, I think. :)
andymcl92 my hypothesis is, that less surface tension should lead to less beading.
Dragon Curve Enthusiast I agree, but since surface area is proportional to radius squared and volume to radius cubed, I suspect the effect would be greater for narrower streams, so lowering surface tension and having a finer flow MAY lead to the same outcome.
What the hell is your profile pic
Steve holding bottle on wall and eating Pringle are soooo stupid and silly moments BUT it’s what makes your channel unique. Great videos!
"Bizarre ripples"? Well now Steve had mastered the power of Hamon
I was looking for a comment about Hamon
HAMON OVERDRIVE
MOTA MOTA MOTA MOTA MOTA MOTA MOTA MOTA MOTA MOTA
Part 3 didn't have Hamon smh
@@mayabartolabac It has, it was when Joseph Joestar was fighting DIO. He used hamon + hermit purple so he can't get touched by DIO
Could you try to capture it in slow motion so we can see how the "standing wave" forms? Does it go upwards? Does it appears in the whole stream at the same time? Is is instantaneous or a "slow" process?
I think it would be very interesting to see :)
Thinnestmeteor it will form from down to up, because information travels through materials at the speed of sound in that medium. So the upper part of the stream won't notice instantaneously that an object has been placed under the stream.
Maybe this is one for @theslowmoguys
I suggest posing this to a fluid dynamics expert. I believe we can model this using Navier-Stokes; has anyone tried that?
Kaedenn My friend is a research fellow working in the field of mathematical modelling of the phenomena involving jets, collision of jets etc.
ya, well my friend has a vagina, but thats not helping any of us rite now is it? @@yashagrawal9309
Anything with viscous fluids is simulated using Navier Stokes. There are many simulation schemes that use it, but surface tension is an additional effect that needs to be added into the momentum equation (the second of the three). I really want to explore this on my free time, but right now I’m having to focus on my plasma research
I'm glad you mentioned standing waves in application to guitar strings! I'm wondering if you would investigate laminar flow in wind instruments, and how air stream might interact with the standing waves within a column of air
8:11 that got me laughing so much
I loved how you provoke reactions with your scene 3:20 that plays with the suggestion evoking a life familiar scene, like when we piss the wall when we were kids.... and then right next silently you gives us that look of " Is not what you are thinking" Ha ha ha ha ha is so magnificently well executed!
I've wondered this for years, but always thought it had to do with the rope coil effect, especially because when you obstruct the stream really close to the source you can almost see a steady twist in it. I would love to hear your thoughts on this theory!
I smoked for about 15 years, but happily quit smoking about 12 years ago. Your candle smoke reminded me of something I saw quite a lot when I still smoked. The column of smoke from a cigarette would sometimes create what appeared similar to laminar flow... sometimes there would appear a kind of ripple in the smoke column and interrupting it would cause the wavelength of the ripples to change. I still don't know why, but think this video might be part of that answer.
5:00 Okay it took me a while but I finally understamd why the curved has less *surface area* than the cylinder formed by the loops. The *perimeter* of the middle part gets smaller, so it has less surface than the full cylinder.
I can't believe how relevant this video is to me. When I saw the thumbnail I audibly gasped and debated whether to click it. You see I noticed this phenomenon years ago and was fascinated by it. On my last day of grade 8 I talked to my science teacher about it and he didn't know how it worked, telling me to investigate it further and maybe do a more organized study on it in the future. I couldn't get further with my knowledge, so I didn't investigate it, but I remained fascinated, occasionally turning the water on the tap in my bathroom down very low and trying it out when washing my hands. A few years later I did a science project in high school on Chladni plates, in which I researched standing waves and actually ended up having a friend who made a working Chladni plate for an in-class demonstration which I still have. And now I sit at a desk looking through UA-cam and I see this video. When you talked about forcing a node at a specific spot and having a standing wave formation, I sat for a few moments with my mouth gaped open. I can't thank you enough for making this video.
Thanks for the story! Glad you got someghing from the video :)
Geez, it was just this last couple of days that I figured out why some bathrooms have higher than average urinals and now I know the name for that bit of science - Rayleigh Plateau Instability.
I've spent plenty of time playing with the laminar flow in the sink and have had these questions run through my head without any answers, so thank you for explaining 30 years of curiosity.
40 seconds in I realize that that's due to water's viscosity, like pouring honey over toast
Edit: And because it's laminar flow, the waves formed are non-chaotic static waves
Wow. You are super smart and stuff.
It's surface tension. When you block the flow, it backs up the stream and it buckles. When the droplet separates from the stream, it snaps the end of the stream closed and the stream acts like a rubberband that sends energy upwards which has the effect of a momentary blockage.
I'm interested to see if this ripple effect happens when the obstruction is a hydrophobic surface.
these ripples have been mystifying me for 20 years!!
thanks a bunch!
What happens if the water has no or very little surface tension? Will it ripple like this?
55Ramius The adhesion of the water to the to an object forces the cohesive properties of water to bend in the most efficient and stable way. Where stable conformations exist, you get standing waves.
Liquids with less surface tension have less surface tension because of a decrease in cohesive properties. This means fewer stable conformations resulting in fewer standing waves, particularly when the distance between adhesive endpoints (the faucet and the bowl) decreases.
Mix a few drops of dish soup into water and try it out.
Steve Mould, this is one of the bloody greatest channels on the internet. You do a great job of explaining and visualising phenomenons and catching my interest. I really enjoyed this video, as I did so many of yours before. Keep up the great work! This is stuff I wish I was presented with in science classes!
As always, awesome video from Stevy
Over 20 years ago, I tried to do an A-level Physics project looking at these standing waves. I didn't get very far with it, though and ended up switching to looking at how pendulums made from springs behave. I've always wondered about this, though, so thank you for investigating it.
Isn't it just water piling up when the flow is obstructed?
Thats just what i tough. Flow is obstructed with finger, water molecules hit the finger, slow down and need to go around longer way, but another molecules are already hitting them and slowing down again, but there are molecules above them that have greater speed so water is piling up? I also think that this bending is in fact a spiral shaped stream, because curvature on the left doesn't cover curvature on the right side of stream or thats just the point of view.
I just checked with my own tap, and it's definitely a spiral. I don't know what that means for the different theories of why the water bends, but it did bother me that the shape with an obstruction didn't exactly match the shape that causes the breaking into droplets.
If this does have something to do with Rayleigh-Plateau instability, then something has to explain the spiral shape. It's still a standing wave, just with one component that's out of phase with the other. And, notably, a spiral should be unable to cause drops of water to break off.
The "piling up" hypothesis seems to fit what I'm seeing. All the outermost water is pushed outward, but its hydrogen bonds pull it back inward at the same time. Along with some small random motion to the side, this could cause orbits to form, closely followed by the orbiting water tending to favor whichever orbit happens to be densest, again because of the hydrogen bonds. A lot like the formation of planets from orbiting dust clouds. And since the water is falling while orbiting, it traces out a spiral.
I wonder if a high-speed camera would show anything useful. If the water does pile up and start orbiting, I'd expect to see the spiral grow upward over time.
Using high fps camera would be nice. I wonder how long can be the stream to actually form the spiral from obstruction point to source and how fast its growing upwards. Would it be the speed at which the water falls down, faster/slower. Maybe the "frequency" of the ripples as shown in this video depends on the speed of water hitting the obstruction point, the further it is - greater speed caused by gravitation - denser the spiral. I wonder also if the direction of the spiral is always the same, and if its the same as water that you let go through a sink hole.
Could you explain the change in wavelength of the ripples as the obstruction moves further from the source?
My initial thought was that the coiling radius might have been related to the velocity of water (an obstruction further from the source blocks faster-moving water, and somehow this translates to tighter coiling). However, this paper (tel.archives-ouvertes.fr/tel-00156591/document, p.24) and my own brief experimentation seems to show the correlation isn't linear.
The standing wave hypothesis could explain the change in wavelength, but you would expect the change to be sinusoidal, not linear. Perhaps a tap just doesn't show a large enough sample size?
I think the reason for the tighter coiling is that the column of water, and therefore the spiral around it, is thinner. Thinking again in terms of orbital mechanics, orbiting closer to the center causes the water to orbit faster, which means it doesn't fall as far before coiling all the way around. Also, since there's less water in a slice of a thinner water column, it's less resistant to changing its direction. Of course, faster-falling water would tend to lengthen the coils, but it looks like, at least at the heights we've tested, thinness wins out.
I'm no expert on fluid dynamics or orbital mechanics, so I might be wrong about a lot of this. In particular, before looking at that paper, I hadn't thought of considering the water to be like a rope. In that case, the explanation is probably more complex than the orbiting model would suggest. And I'm not really sure how to test what I've proposed.
I think you're on the right track. I think the missing piece of the puzzle is the disruption of acceleration. The column of water in free fall will get thinner and thinner as it falls and accelerates until it eventually breaks into droplets. So you're stopping the flow and forcing a rapid deceleration of the water at the end, forcing the node as you put it. The first node creates a deceleration of the water behind it, and subsequent nodes form. To prove this you could use slow motion footage and if I'm right the nodes will appear one after the other starting from the bottom. The waves get smaller as you go down the column of water because you're allowing the water to reach a greater speed before interrupting it.
Ripple, you say?
I'm amazed at how interesting you make a seemingly trivial topic! Much respect Steve.
Interestingly, the ripples don't seem the same on both sides.
It’s really fun to see analysis of things I wondered about as a kid, and haven’t known for years.
It looks to me like it has to do with the viscosity. Does it change with temperature?
I also think so. And if you look closely the the "waves" are shifted from the left to the right side of the stream unlike with the droplets. In 3d it would form a spiral, just like if you pour honey for example (just a smaller spiral).
Ricci flow, Poincare, Perelman, Bose- Einstein condensate all similar to what you research.
J,P,Yodd God's finger pinch holes. Like does straw has 1 or 2 holes.
Hollow grammic materialization of BE glue into 26 different mass particles.
Hole in a hole in a hole.
E🎱 math, primes, Riemann... all is connected.
I love all your work. Learning is more fun the way you do things. Thanks!
0:30.
HA, now I can unlock your phone
This was ALOT more maths and science than I was expecting...
Interesting.
I totally love your educated approach to things you're maniacally fixated on.
3:28 I had to rewind to understand that glare. I was thinking applications of industry, not urination.
This was very intriguing. If more videos were exploration rather then having an actual answer, I would enjoy that far more then getting an answer. It actually convinced me to get up and go to my sink and start experimenting. Sadly, my sink is not giving me a water flow like yours so I have bad results, but I plan to gather some materials to go farther. Awesome video!
Since I’m a kid I had to watch the video three times to understand 😩😫
So much science has been put into a running tap. I'm impressed.
*notices the bulges in laminar flow*
Scientist: õwó what's this?
The guitar string example is pretty on point, it's also consistent in that as you move your finger closer, the frequency of the wave increases.
Wait, printers actually work?
No no, I'm just saying *if* they worked, this would be how.
PC LOAD LETTER
I used to turn the tap down to the thinnest laminar flow stream and then slowly push my finger up the stream in order to push the waves up until they touched where the water emerged and then that would trigger the Rayleigh-Plateau instability and then the water flow would remain broken without changing the flow rate (opening the tap further). I tried the reverse and could sometimes get it to shift state back to laminar again. I didn't know any of the physics was behind it so thanks for diving deeper for us!
>bizarre
>ripples
This IS a JoJo reference, admit it.
So my thinking is: Since you put something in the way of the flow, the molecules get slowed down(maybe even get pushed back a little bit. So the molekules in the front of the flow get slowed/pushed back, but there are more molekules coming at unchanged speed from behind, so the molecules bottle up and need to go somewhere and form the bulge. If you look closely at 1:17-1:45 you can see, that if you hold the object in the middle of the stream, the bulges are shiftet (when there is a bulge on the right side, there is a pinch point on the other side and vice versa), because the one side is obstructed while the other can just flow normally. And if you hold the object directly under the stream you have the bulges lined up (1:36), since you obstruct the flow on both sides equally. In a confined space (a tube or a channel), if you put an obstruction somewhere, it would create turbulences, since the bottled up molecules cant go anywhere and swirl up. In an open stream however they can just form these bulges because there is nothing in the way.
Can someone debate?
That is not the explanation I thought of, because the ripples become bigger as you get closer.
So I figured it must be dependant on the force with which it hits the obstruction.
And that increases with the height it's been falling from.
If you move your finger against the stream it also makes the ripples bigger (though I'm unsure, you guys need to check)
Maybe the tighter ripples are higher energy because they're a higher wavelength ? Or is it bigger ripples that have more energy ?
Besides the science in your videos, I really enjoy your explorations of the boundary conditions between under- and over-played humor!
A question I never would have thought to ask, but which I've always wanted the answer to
Great video! When I was a kid I was able to watch and play with this for hours. After watching I have the feeling that velocity has a crucial part at this phenomenon as well. As the water moves down it's velocity increases, so the stream is constantly stretching, so this is the reason it gets thinner and thinner on the way. Wherever it hits the object, the flow slows down, so it gets thicker before the touching point. Whenever the object is closer to the source, the stream thickens, whenever it is farther it grows thin. I assume when it gets thinner it gets more unstable, and after a certain length it breaks into droplets. Maybe because it reaches the speed it can not be laminar anymore, and the occurring turbulence breaks the stream up.
When it's short, I also think about the stream as a water in a thin flexible and elastic pipe, wherever it's diameter shrinks I assume the momentum of the flow will produce extra pressure on the upward wall of the thin bridge, while the quick deceleration at reaching the object creates an extra pressure on the downward wall of the thin bridge. While at the object it looks like when two separate water bodies are just touching each other.
I just wonder why the pattern shows up only at the end of the stream, and why it dies after a several ripples?
I love that I wasn't the only one wondering... now explain to me why a slow stream of running water flowing down a flat plate of glass so closely matches the motions/meanderings of a flowing river. Cheers!
Man I love your comedy, specially the moment of “ No, I’m not pissing on the wall, damn it”.
You are awesome 🙇
I know this video is two years old now but I can't help but notice that the standing waves seem to spiral clockwise from top to bottom. I'd love for you to revisit this as I feel there is more going on? Excellent work btw 👌
As I've seen a couple of other people mention below, it looks like it also has to do with the viscosity of the fluid. When something is put in the way of the stream, the fluid nearest the obstruction can't get out of the way as quickly as more fluid is coming down, so it causes the stream to bulge where fluid is piling up. But that piling up also increases the pressure (due to surface tension preventing further bulging) and that increased pressure increases flow which reduces bulge. You end up with a series of bulges and pinches in a pattern that balances these two flow rates.
If the phenomenon you mentioned was related to this one, you would see the flow become thinner and thicker symmetrically. In this case it doesn't look like the stream is stretching, but rather crumpling (like soft serve ice cream). The diameter remains even, and doesn't bulge along the generated spiral. I think you were on the right track when you described the layers of laminar flow.
On the outside, you have a slower-moving layer of surface-tensioned water, almost like a stretchy rubber hose. When you interrupt the stream, this water piles up on itself, but because the surface tension won't let that outer layer shatter, it keeps the inner layers flowing laminarly in a crumpled path (again, like a thin rubber hose) until it interacts with the interrupting surface.
The phenomenon becomes tighter lower down because the water is moving faster, and there is more force being applied to the outer, springy surface-tension layer, causing it to compress more tightly. I imagine the fact that the cross-section is smaller lower down also means that the water can pass the obstruction easier, which lessens the l length of the pile-up further.
I have always been fascinated by these ripples.
I imagined the ripples as energy reflections going back up the stream after hitting my finger. The water molecules are speeding down and hit my finger and they get reflected back up, but they run into more water that is moving down, so it makes a chain reaction moving upwards but loosing some energy as it goes up into the oncoming stream, that's why the ripples get larger as they go up.
My hypothesis on the "standing wave" is that when the flow touches an object, the water at that point drops its speed due to the adhesive property of water. So, due to this "touching" and "slowing down" the water above it somehow... bounces back up because of this "water collision" (?). Sorry if my explanation is too complicated, but it's sorta like people in a line- assuming they're all walking, when the person in front suddenly stops or slows down, the person behind collides and sorta "bounces off" of the person in front... And this is what's happening in that flow of water; that's also why the farther the object is from the start of the flow, the less "collision bumps" there are.
That's just my hypothesis though ^-^
I highly recommend reading Pollack's 4th phase of water. This has bearing on so many things as to bring you to wonder.
I did notice this effect when I was a kid. I’m glad other people notice these sorts of things and investigate this
If you look at the ligh in the stream it seems to be bent, not bulging. The surface tension may be enough that the water behaves more like a chain.
Your wonderment of the world around you is inspiring and contagious. I love how all your videos show that you needn’t have a huge lab to observe and participate in science. Thank you
I don't know why but every time I watch a Steve Mould video I get inexplicably paranoid of jumpscares... No idea why.
Oh, it's coming...
I noticed this effect literally half a century as a kid playing around with the faucet. I'm not sure I understood the full context of your explanation re: pressures, but I intuitively buy the standing wave theory. It does seem to have that sense about it.
Love your videos, Steve. So glad you never grew up and became ‘sensible’! This laminar flow video which I have only just discovered reminded of another conundrum; when bubbles rise in my aquarium they do not go straight up! The bubbles seem to spiral up on a helical path that may be related to the size of the bubble. I wondered where the lateral force that wobbles the bubble from side to side comes from?
I'm really fascinated by the image at 5:52. The water stream is doesn't interact with the glass right underneath it, but is actually "sucked" onto the glass to it's side. I would assume this is also due to the high surface tension properties of water, but it's really interesting to see!
One of my goals in life is to get Coffee with Steve and talk about the wonders of life
Your conclusion and link with black hole makes me think about the wobbling plate of Feynman
2:24 Cool thing about candles - the "smoke" that you see when you blow out a candle is vaporized wax. You can demonstrate this by blowing out a candle and then touching a flame to the stream. It will light, travel down the stream, and relight the candle.
Here is something I encountered a long ago: Get yourself a length (about 1 metre) of a hose with wavy wall (similar to these waves). Rotate that hose above your head (that causes air to be pulled through the hose via centrifugal force) or simply blow into the hose. The hose will start to "sing" (emit a tone). If you rotate it faster (or use a blower that produces high speed air stream), the tone suddenly jumps to a higher tone (maybe the original is a base frequency and the higher one is a multiple of this base frequency?). On the other hand a hose with a flat (non-wavy) wall does not sing at any speed of flow through it.
Curious people like you are a pleasure to watch
I liked watching this. Two things: -
1. At about 00:39 we see the water curve around the finger. This shows the Coanda effect, which I remember reading about in Scientific American way back in the issue of June 1966 (thanks Google) and have never forgotten.
2. I think there is a contribution of pressure change at both when a drop separates and when the flow meets an obstruction that generates a reflected pressure wave back up the stream. Backwards propagation of a pressure wave is well-known. That is why sometimes you have to brake suddenly on the motorway, then speed up to find no visible reason why people ahead were braking.
I realise drop separation in a simple downwards flow and encountering an obstruction are different, but still think pressure reflection is common to both.
No, three things! As I understand it, water is both one of the simplest molecules, yet still not fully understood after all these years of Chemistry and Physics. It seems we are still at the observational stage, as per this post, since computer modelling remains both varied and not resolved at the moment. As an atheist, I think water competes with the Sun as something worthy of some kind of worship :-)
I was 10 years old ...
Without a cell phone or other things to do while you are at the toilet, it happens that you experiment. I realized that if I took my finger in the water from the tap in front of me, With a small amount of water flowing, it became this phenomenon. From that time until now I have thought about it without spending too much effort. Suddenly this explanation came up. Thanks
Hey Steve, i have also noticed that if reduce the flow rate of the stream until it's just at the brink of starting to break off but is still laminar, it'll remain laminar until you bring in an obstruction after which it will not go back to its state of laminar flow even if the obstruction is removed. And this phenomenon is more likely to occur if the obstruction is closer to the source of the stream. To get back to laminar flow, you have to stop the stream altogether and reset it.
Steve's videos are the explanations of the things that I found out in my everyday life. I used to turn on the tap very slowly in my bathroom, adjust the flow rate until I got the perfect ripple, and then stare at it. Often this would keep me staying inside the bathroom for an hour or two, my mother would knock on the door at a regular interval of 5 minutes. Often she screamed, "It has been so long, what the hell are you doing? GET OUT NOW!" 😂😂
Great editing. And explanation, superposition of videos, and the case studied, and the subtle jokes.
On the top of a shower head, its droplets are near each other. As they accelerate downwards, they begin to separate due to gravity.
Furthermore, there is an attraction between water molecules (responsible for the surface tension), which keeps the molecules in chunks, so a chain of spheres with different velocities makes this pattern.
At 3:11 and 6:33 is visible that the bottom chunks are slightly wider than those on the top because they accelerated more. The big one below became so far apart that it is just about to split off.
Surprisingly, at 3:16 and 5:54 the pattern is inverted, the wider ones are on the top. But is noticeable that a tilt appears; the line is bent (at 3:16) and there is a twist (at 5:54): so there is an attraction. Thus, this phenomena becomes very complex.
Another cool water faucet phenomenon I notice is when filling a container (or cup) of water. When the waterline gets close to the top of the stream, it turns from a cylinder to a cone flare at the bottom. It's like the force of the water pushing up against the stream evenly distributes across the edges, causing the sides to form a cone.
Always enjoy your videos. You actually take the time to experiment and test all the things I see as a passing curiousity. Keep doing what you're doing!
I'm already a subscriber of your channel and hadn't watched this video of yours. But recently when I was walking down a slope and water was flowing down slowly. I stopped to observe and it had these very small ripples in front of the waves. When I was searching about that I stumbled upon this awesome video of yours. You explain it really well and it has quite a lot of parallels to my question.
Thank you Steve!
Really interesting video. I think the reason the ripples get more "squashed up" when you move the obstruction further down the flow is due to a doppler-like effect. The waves propagate upwards from the obstruction at some wave speed, relative to the speed of the water. When the flow is slow (i.e. nearer the tap) the wave speed is much greater than the flow speed and the wavelength we observe is hence longer. As we move down to where the flow is faster (because the water has been falling a longer time) the flow speed become close to the wave speed and so the wave fronts are closer together, giving a shorter wavelength. If you went further down, to where the flow speed was actually greater than the wave speed (torrential flow), this effect wouldn't happen.
6:30 OMG this is so amazing! I never thought of that!!
And I discovered (probably some people have done it too) that if you get closer to the source it starts to go drop by drop then you can stop to stop the water flow and it will keep going drop by drop a few seconds and they go back in stream. Also you can open the tap a very very tinny bit and you'll see that the stream stop at some point and it becomes individual droplets. There must be some conection going there.
I love that you show your humour through your videos. I'm hooked!
Hey steve, see the small patch on front of the bubble at 5:13 where the light is reflecting and refracting? I have found this interesting and beautiful for a long time. It would be awesome if you did a video on this.
What I have observed is if you just have a flat vertical bubble film in a bubble wand you can observe the Colors filtering from bottom to top. First is multiple bands of teal and Pink then bands in this order: green, pink, yellow, green, blue, purple, pink, orange, yellow, light blue, dark blue, dark purple, orange-ish brown, white, silver then clear then it pops; seems to always happen in this order. The best way to see vibrant colors is hold the film so it is reflecting a bright light. If you blow slightly on the bubble film the colors swirl and look kinda like a kaleidoscope.
Something I just noticed in this video is that the reflection in the back at 5:13 is yellow-green and purple this must be from passing through a second layer of bubble on the way to the camera. So now I'm wondering how many layers you could line up and how many times the color will change or maybe end up repeating.
I think the reason this happens is that gravity is pulling the small amount of water trapped between the two layers of surface tension and getting slightly thicker towards the bottom. I think the different thicknesses reflect/refract different wave lengths of light, probably even be IR/UV light being reflected from the clear part that we can't see.
It could be for the same reason that honey curls on a surface and the amount it coils after pouring changes with different viscosity. Maybe this is the water attempting to coil but due to its low viscosity it simple appears as ripples.
Very interesting. Though I feel something is missing here. You talk about the Reyleigh-Plateau instability, and how it splits the stream in chunks, due to surface tension. But I feel there is an other actor on the scene: fluid viscosity. Somehow it helps surface tension kind of pull on the liquid to keep it together, and somehow it also prevents chunks from splitting.
There was a video this or previous week on Smarter Every Day where Destin explains a phenomenon that I find really similar: honey coiling when you pour it in thin laminar flows. His explanation is more centered around fluid viscosity and how it pushes the stream around to produce these coils.
I can't help but think this coiling phenomenon and those standing waves in water that you show are somehow related.