Pop-Pop Boats Are Weirder Than You Think

[@SteveMould]

If you're wondering why the boat never cracked under thermal stress, it's because they made it out of quartz glass! How cool is that! You can also discuss this video on REDDIT: stvmld.com/xf-isn5j Check out Anker 521 Portable Power Station: ankerfast.club/3vq4RRe (#ad)

[@sixtenwidlund4258]

Nice video!

[@robertschnobert9090]

I love you, Steve! 🌈

[@khadimhusen]

Great video, I wonder what would happened if heat is given from the top side.

[@littlebacchus216]

How much did custom made quartz glassware cost? When I was at uni we had to sign glassware in and out and pay if we broke it... I broke so many Graham condensers.

[@nobody-ek5bx]

but what happens if you make a T sektion with the pipes unter the boat and use 4 one way valve to use the sucktion at the front and the push at the back of the boat? is it better or more eficient now?

[@arbitraryconfusion]

Those glassmakers did an incredible job.

[@reidflemingworldstoughestm1394]

probably the most notoriety they've ever had

[@pleasedontwatchthese9593]

i would like a video seeing how they made it

[@schnizzyfizz7832]

@@pleasedontwatchthese9593 Gas torches (maybe oxygen/acetylene to get extra high temp, idk what quartz glass needs to melt), bending tools and various diameter glass tubes. I saw a video from a university where they made custom lab glassware. Also proper cooling to avoid cracking as with all glass. So prob some oven to let it gradually cool. Idk what that is called, but I am very sure there is all kinds of glass making terms. Glass is a fascinating material.

[@anthonynelson6671]

Knowing just a little of how tricky glass can be I was wondering how much that little glass boat costs. I've seen how expensive high precision lab glass can be. It's an interesting yet different world of things.

[@comradegarrett1202]

@@schnizzyfizz7832 the oven is called a kiln and the process of putting glass in a kiln to keep it from cracking is called annealing.

[@PhantomSavage]

Excellent. If I ever find myself on a deserted island with an oil drum, a couple of pipes, and enough wood to make a raft and bonfire, I know how to escape.

[@JD2jr.]

Now I want to see somebody build a human-size one of these...

[@blackmber]

That’s right, put your signal fire to _work._

[@flagmichael]

@@blackmber "I don't know, Captain. The signal fire seems to be moving!"

[@besquareorbethere8093]

Hopefully you can keep that fire going long enough to cross the 7 seas.

[@mucia55]

Just tell me the exact max d of the pipes to maintain the capillary effect of water preventing the vapor to move over inside it and I'm building it.

[@Eidolon1andOnly]

I'd assume that the shape of the boat also plays a factor in its forward trajectory as the bow of the boat is more streamlined for less resistance while the stern of the boat is not.

[@khalilahd.]

Yeah I definitely agree

[@Lezenda]

oh well, there I go with my comment (17 min after you), thinking that I am the smartest :)

[@archbox8593]

In that case it would be interesting to put the tube openings in the front and see if this would make it still move forward?🤔

[@chorusofoddities]

He cut the bit where he mentioned that from the video, thinking it wouldn't interesting anyone, he said in another comment

[@bbugl]

making a symmetrical boat would be interesting.

[@kenbobca]

I am 69 years old, when I was a child my father brought home a metal Pop-Pop boat. I now have one to amaze my Grandchildren. Thank you for your video explaining how they work.

[@blaisebaileyfinnegan8202]

I'm 200 hundred years old, when I was a child my father was a mercenary returning from the Java War fighting for the Dutch and he brought home a metal pop-pop boat. I now have one to amaze my great-great-great-great-great-great grand children.

[@buckfizzard291]

@@blaisebaileyfinnegan8202 why would you disrespect the man like that

[@blaisebaileyfinnegan8202]

@@buckfizzard291 Because I can, homeboy.

[@buckfizzard291]

@@blaisebaileyfinnegan8202 well that's immature

[@amarnamarpan]

Your grandchildren are so lucky. ☺️☺️👍🏼

[@v_Shami]

I remember seeing one of these in ponyo when I was little, I thought it was so cool. Still do actually, would love to have a little boat like that big enough for me to actually fit in

[@Laurpud]

OMG, right? That would be so cool to putter around in!

[@rachelcookie321]

Wait, they have one of these in ponyo? I only watched the movie a couple years ago and don’t remember seeing this!

[@v_Shami]

@@rachelcookie321 yeah, it's how sosuke and ponyo go around to look for his mom once the water rises

[@rachelcookie321]

@@v_Shami oh, I thought that was just a regular toy boat. I didn’t realise it was one of these.

[@korwynze6288]

same i thought of Ponyo right away! ahh what nostalgia

[@chorusofoddities]

No-one could be disappointed with any good visual explanation - even if it makes your channel a 'transparent version' channel!

[@khalilahd.]

Always the best content 💛

[@desu38]

Right? It's like those cg graphics, but better.

[@amicloud_yt]

Better than "pour things out of jars" channel

[@sethgwiyo2250]

kzbin.info/www/bejne/oaLVgmWqnZx4gKs

[@desu38]

@@amicloud_yt Well, I like NileRed

[@MaxineInYourWifi]

i have only seen this toy from Ponyo and it has been in the back of my mind. thank you for the name of it, and explanation of how it works.

[@AndrewSmithThomas]

"The batteries are just there for weight" - exactly what someone would say to hide their perpetual motion machine. You can't fool us!

[@truongnguyenhongnhat6590]

ok

[@leyrua]

😆

[@truthbetold1855]

Haha yes, the ONLY thing he could find.. HAPPENED to be two AA batteries.. SUUUURRREEE LOL I think they call this hiding it in plain sight 🤣 kidding.

[@hankholschuh7987]

@@truongnguyenhongnhat6590 it was a joke genius

[@bstikkel]

If you do not believe the batteries really are only there for counterweight, have a look at the metal version. We had several of those and it really works the way it is demonstrated.

[@plaguepotato6624]

I was introduced to the Pop-pop boat from Ponyo and always wondered how it worked. Amazing video, thanks for the explanation!

[@Mattguy-lg3nr]

yea

[@spunkyspaz]

Ponyo brought me here too. :)

[@fotiacruz3911]

W movie

[@kennethsizer6217]

Same!! 👍

[@its_aj251]

Same

[@Nighthawkinlight]

I saw a clip or two in this video with the engine running with asymmetric amounts of water in each tube (3:35). That's very strange. Other thermoacoustic engines require pretty precise resonance matching between the engine cavity and the load to get any work done. In this case you've got two mismatched loads with competing resonances somehow popping at the same frequency. I'm guessing the mismatch must be minor enough to force synchronization but would like to see further tests. Does the amount of water in the tubes effect the frequency of the popinating? If you make one tube a little longer than the other so it contains more water by default will it still run?

[@SteveMould]

That's a really good point. Happy to send you the boat if you want to run some test. Drop me an email if you're interested [e-mail]

[@littlejackalo5326]

How does this comment not have a single like? Why was it buried? Nighthawk in light is a huge KZbinr who does similar videos and this comment should have way more likes..

[@Lets-Talk-Law]

@@littlejackalo5326 The bot presence is strong on youtube

[@Resonanttheme]

That brought to mind a clip "Stirling Twins Pogo Engine", two syringes driven from a common chamber, one deciding to bounce higher then the other adjusting displacement.

[@Resonanttheme]

@@MadScientist267 And the heat transfer properties of quartz is different. Ideally, if you could maintain a steam hammer effect, you'd get a lot of thrust.

[@Sanjay-eb6fe]

I've played with a dozen of these when I was little. They used to keep me entertained for hours. I have forever been wondering exactly how these boats worked. At last your glass boat has put an end to that. High five !

[@ezioboiz-ieatchildren-]

You should already know this because this is taught in physics 💀

[@DemoniteBL]

@@ezioboiz-ieatchildren- Not everyone learns the same things in school 💀

[@ezioboiz-ieatchildren-]

@@DemoniteBL wait so you're 9 year old?

[@DemoniteBL]

@@ezioboiz-ieatchildren- ?

[@ezioboiz-ieatchildren-]

@@DemoniteBL i mean the physics taught in this video is basic physics you're taught.

[@jacoblawrence9145]

Another possible reason for the oscillating motion moving the boat forward: the shape of the boat generates much more drag being pulled backwards than it does being pushed forward, so the net effect over a full cycle is in the positive direction.

[@233kosta]

It's not really going fast enough for pressure drag to be significant, at that point it's mostly viscous drag which is symmetrical. Even if that wasn't the case, the boat would have to stop and reverse direction for the drag bias to have any effect at all, and it doesn't. It just keeps going.

[@fireballxl-5748]

@@233kosta Disagree. Simply disagree and would have to see empirical evidence.

[@233kosta]

@@fireballxl-5748 If you want "empirical" evidence, go run an experiment. I'm not paying for all that instrumentation just to prove a point to some rando on the internet who doesn't know what a Reynolds number is. Your choices are to either learn fluid dynamics and kinematics, or pay for an experiment everyone in the industry sees as a complete waste of effort. I suggest you start at Anderson's Fundamentals of Aerodynamics.

[@fireballxl-5748]

@@233kosta What "experiment"? Suggestion? You're the self called expert.

[@233kosta]

@@fireballxl-5748 You asked for empirical evidence, that is how you get empirical evidence.

[@JimC]

As you've probably already been told, the "water flowing into the pipes from all directions" explanation that you rejected is the same reason Feynman gave as to why his s-shaped water sprinkler wouldn't work backwards. So it might be interesting to run that experiment in a clear box, like Hero's engine in reverse.

[@anotheral]

YES SOLVE THE FEYNMAN SPRINKLER PROBLEM FINALLY!

[@Lastielion]

Any excuse for a clear box :D We all love that sweet, sweet visible physics

[@jeeeeeeeeeeezus]

You'd see nothing illuminating doing the feyman sprinkler transparently.

[@resintom852]

@@jeeeeeeeeeeezus you’re fun at parties I bet.

[@shawniscoolerthanyou]

@@jeeeeeeeeeeezus adding dyes to the water could give a qualitative feel to the asymmetric flow between in and out.

[@colincenge]

You glossed over the flexing metal making a popping sound, but that compliance is actually another spring in the system. I believe this added spring sort of amplifies the steam effect which is what makes the metal boat faster than the glass one.

[@DJZofPCB]

On the head of the nail.

[@SebastianWoodard]

man I love KZbin. you can learn so much stuff just by reading the comments

[@SebastianWoodard]

but I assume because of the motion, it creates a bit of a vaccumn to assist th oscelation?

[@DavidMartin-jr8nd]

I bet the glass boat is also much heavier. It might have worse fluid dynamics as well.

[@altruismfirst6489]

It is a basic version of a Sterling engine with the metal acting as a piston . This flex is vital as is the cooling properties were and metal pop is a frequency with some other non audible frequencies that are yet to be observed in the overall propulsion total percentages. A glass version defeats many observations and in fact indoctrinates the real working aspects of the metal original. An infrared camera using a metal unit will be interesting.

[@ShadowsOfTheSky]

I always like to put my guess for the big question on these types of videos… I’m at 7:30 and we’re about to figure it out. Basically, even though water is going in and out, theoretically putting the same force on the boat each time in opposite directions, we should stay still or perhaps shift back and forth slightly. However, because of the shape of the hull, there is very little resistance when moving forwards, and a large drag resistance when moving backwards. So even though the same force is imparted on the boat, the boat slides forwards easily, but doesn’t ever want to slide backwards.

[@bencejoful]

That was my guess as well

[@Games_and_Music]

And funnily he didn't even mention it. Although it's not the main reason, but it's definitely a big part of hydrodynamics overall. Now it might be kinda "interesting" to see a pop-pop installed backwards and see which force wins. Will the 'engine' win, or will it slowly wander backwards or sideways because of the reverse installment and contra hydrodynamics. And how much is needed to turn that result around.

[@pyrotas]

Actually more than resonance I think this is a nice example of limit-cycle oscillation, where a steady supply of energy (from the candle) produces an oscilatory motion.

[@sethgwiyo2250]

kzbin.info/www/bejne/oaLVgmWqnZx4gKs

[@velbythorngage]

Yeah I wish he'd gone into more detail there, I still don't get how a constant force from the candle results in oscillation, I'd expect the expanding gas to reach equilibrium (kind of like applying a candle to that syringe, it would expand but wouldn't oscillate)

[@acters124]

​@@velbythorngage Candle does not provide a true constant energy to the glass and gas inside. it is providing an oscillating energy to the glass and inside gas that you can visibly see. It would be great if there is a way to pinpoint heat transfer to a single point without it leaking to the surrounding environment. however, entropy will exist in any lab environment. This whole boat is a practice in how imperfections provide a oscillation in energy levels in the system. How one uses the oscillating energy is a mystery, in this example it is used to drive a boat forward. Another example of using oscillating energy sources is in an AC system. In an ac system, an oscillating energy source changes pressure from one side to another in a continuous motion.

[@sumdumbmick]

@@velbythorngage he'd have to know wtf he was talking about to go into more detail, though.

[@lucasbiaggini]

@@acters124 wouldn't a resonating frequency be constant, while random oscillations would be random? I think simply measuring the frequency of the popping sound in one of this boats could pretty much settle it.

[@TimeBucks]

Very interesting & well made as usual

[@coryman125]

Reminds me a bit of a pulsejet engine, the way it oscillates to produce a net force. Obviously it's very different in a lot of (very big) ways but I can see some similarities in how they work

[@reubeng2110]

my favorite was in the 50s and 60s scientist wanted to launch huge payloads into space using pulsed thermo nuclear explosions Kennedy shut that program down they did nuke testing and it works just like a nuclear powered missle

[@ruskiwaffle1991]

@@reubeng2110 orion right?

[@Nikarus2370]

@@ruskiwaffle1991 Well Orion IIRC was having a rocket in space propelled by dropping nuclear bombs behind it. There was another project exploring nuclear salt water rockets. Basically a nuclear reactive uranium (or plutonium or other) salt would be dissolved into water and stored in tanks with a lot of boron or other material to lower reactivity. Basically would work by spraying the fuel out the back through a nozzle lined with a moderator (like graphite) to cause a constant flow nuclear reaction out the back of the rocket. Scott Manley has a good video about it IIRC. A 3rd, (more feasible, and tested, adn I think Space X was makign some noise about bringing it back up) option is Nuclear Thermal. Instead of mixing fuel and oxidizer to burn (to make heat) to propel the rocket. You use the heat of a nuclear reactor (one running in a controlled fasion, and not actively exploding) to heat up your propellant.

[@JohnDoe-rx3vn]

i think there's plenty of reason to call it a pulsejet

[@GeneralElecTR0N]

STIRLING ENGINE 😆

[@collomps]

I think the boat has a shape that helps forward movement and not bacwards, so it will tend to go forward even if you apply the same force in both directions.

[@Layarion]

easy to test, just put this in a box and see if it still moves

[@beaclaster]

@@Layarion one annoying thing is the word is "help" not "essential"

[@Games_and_Music]

@@Layarion Yeah, the box will still move forwards, but probably less fast, or less 'guided'. The point about the directional flow of water is still true, so, like beaconblaster said, not essential, but definitely beneficial.

[@bernieshort6311]

This was an interesting video for sure, one which I would never have believed had you not produced the glass model. From model engineer books I read as a child, some 55 years ago, I was led to believe that one tube was fixed into the cylinder at a slightly higher elevation, just a tiny amount and this in turn caused one tube to suck in water and the other to expel the water and vapour causing the forward momentum. So, I thank you for clarifying a miss held perception I have had for about 55 years or so. I am a marine engineer retired, yet I still held this belief to this day. Amazing really. Thank you for this video.

[@ransapar2259]

Oh I've always wanted one of these after watching Ponyo when they turn one giant and use it as a real boat! I wondered how well it would work if a large version was made

[@groggers]

That's where I first saw these too! Led me to buy one on a trip to Berlin, but regrettably I've not yet tried it after 4 years... I think it's about time

[@Gammix]

If it weren't for watching that movie, I probably wouldn't have clicked on this video

[@Book_Thoughts]

I found you guys! I was looking for anyone who had watched Ponyo. I want a giant one two.

[@Fuddleton]

There is a very critical part you're missing. The resonance is controlled by the bulk modulus of the fluid. In a glass chamber, you purely have the bulk modulus of the gas in the chamber. The metal pop boat has a variable stiffness based on the size of the diaphram, which tunes the resonance to that of the heat input of the system.

[@the-real-zpero]

Interesting 🤔 Explain it again, but pretend I'm 15 😁

[@caseclosed9612]

I second ZPERO's motion for elaboration, but like a layman version please lol.

[@unfa00]

What is a bulk modulus?

[@hjertrudfiddlecock4394]

@@caseclosed9612 explain it to us like we're a slow cousin! please Fuddleton

[@The_Rising_Dragon]

@@the-real-zpero So oonga bunga explanation is, that different material sound different when you hit them. Water if flow at certain speed, within certain vessel, it makes same vibration as material. Glass is not same material as plastic, so different shape required, or water need flow to be faster or slower! Capiche? EDIT: Also heat be important for good popping!

[@davesunhammer4218]

The drawings you refer to with the metal tank show a tank that is very flat with a height that is very similar to the tubing (~1D in height and only a few tubing diameters in width), and is slanted down towards the tubing. Your glass tank is several times the tubing diameter in both height and width, and doesn't have the same fluid dynamics as the metal tank. The tubing in the glass system are perpendicular and not tangental to the tank, again causing different dynamics. These changes might acount for the tank not cycing like the metal system. However, the end result is "the same" type of oscilation but different efficiencies occuring in different locations.

[@harrymoyes5069]

I think the top of the metal tank is also part of the resonant system, adding another enhancement to the system, missing from the glass boat. I'm guessing that it helps to contribute the pop-pop resonance notable in the tin boat, and absent in the glass version.

[@OntologicalQuandry]

Just a small note that the natural frequency of a system is not the same as the resonant frequency. They may be close, but they are not the same and can be calculated depending on the energy source driving.

[@SteveMould]

Good point

[@kain0m]

Also, the initial phase shift doesn't matter. If you have a energy supply coming in near the resonant frequency of the system, it will align it's phase _very_ quickly.

[@trstmeimadctr]

I would be incredibly interested to see someone make a full-size version of this propulsion method

[@icouldntthinkofagoodname7216]

I was thinking of a remote controlled rudder boat toy scale at first because the bigger it is, the cost also goes exponential.

[@educationalpurposesmostly]

came here to say this

[@TheCookiePup]

I'm worried that you would need a huge fire and/or the oscillation would be very slow, but I imagine you'd still get some forward motion.

[@pleasedontwatchthese9593]

@@TheCookiePup maybe a lot of small engines

[@SharpAssKnittingNeedles]

@@pleasedontwatchthese9593 Great idea!

[@marthabenner6528]

I've always wondered (like since I was three) if one could make a person's size pop boat. In Hayao Miyazaki's "Ponyo" the little boy has a person size pop boat, my dad thought it was the cutest thing.

[@zonesproductions]

It was the cutest thing 😄

[@JimmyZeng]

To be precise he had a regular sized pop boat, Ponyo used her magic.

[@joecool4656]

Oh you definitely could make a human sized version of this. It would work

[@BierBart12]

Imagine having a nice wood campfire in a little metal stove under the tank

[@DyersEve726]

@@BierBart12 roasting marshmallows while taking a boat ride. Brilliant, lol.

[@harryf9885]

This is very interesting, reminds me of a pulse jet, both initially seem like the forces should be balanced and no thrust should be produced, and both essentially consist of just a cleverly engineered tube.

[@jeanpaulceulemans9973]

pulse jets expell more gas mass than it takes in because the burnt fuel components are also going through the tube unlike this construction which has external combustion. That said, I still think he's wrong and the asymmetry of omnidirectional intake versus directed expulsion generates the thrust This also applies to a closed pulse jet as part of its thrust generation imo

[@gaminawulfsdottir3253]

9:41 It would be interesting to see this done with the tubes closed off by a flexible membrane, to preclude any possibility of water being sucked into the tubes any appreciable distance.

[@charlieevergreen3514]

I’m wondering if dampening the oscillation would nullify the thrust. I’m guessing it would but I’m not certain.

[@thebonedawg2808]

@@charlieevergreen3514 I'm not up on my physics but I think due to the inverse square law as soon as you close that thing the valve pressure would be so high It just blows back open, but at half pressure.

[@greenaum]

Doesn't using red water demonstrate that? You can see that most of the water in the tubes remains the same water, once it's up and going. You can see that none of the water from the tank it's floating in gets in there.

[@gaminawulfsdottir3253]

@@charlieevergreen3514 That's what I was curious about.

[@gaminawulfsdottir3253]

@@greenaum No, I really can't tell from the dye whether outside water is diluting it, or if so, how much. Mainly I'm interested in how much of the motive force is generated by allowing water into and out of the pipes, or whether it's more of a vibratory function that can just as easily be performed by a membrane.

[@borincod]

There is a similar "cancellation" effect during expulsion phase as well as during the "suction" phase. At the final point of the expulsion phase, there is negative pressure difference in the chamber, that will later suck the water in the tube. While negative pressure difference holds in the chamber, the vapor/air inside it "sucks" boat backwards (or in other words, stronger atmospheric pressure pushes the boat backwards). So, the given explanation of the boat propulsion is not complete.

[@tau9632]

Came to the comments to say exactly this!

[@johnineson]

My gut feeling was that that explanation was wrong. For me, a more logical explanation for forward motion is the asymmetrical hydrodynamics of the boat. Going forwards, you're pushing the streamlined prow through the water, whereas backwards is is trying to force the flat stern against it. Even with exactly equal forwards and backwards impulses, I would expect net forward motion. The toothbrush is a good analogue. The bristles are sloped backwards, making the friction asymmetrical. Push backwards and they will tend to grip; forwards they will tend to glide.

[@hanvyj2]

@@johnineson a good test of that theory would be to have the tube exit the front of the boat. It should still go "forwards" if that was the case, and it was the hydrodynamics, whereas it would reverse the direction of the video exposition is correct.

[@enderyu]

Of course there is no total cancelation! The water being spat out will inevitably mix with the surroundings. Its not like it is sucking in the same water it just ejected out

[@ewicky]

I also came to the comments to see if anyone else was totally thrown off by his explanation of "only a cancellation in one of the two phases of the cycle". Like, huh?!?

[@Skarry]

Fascinating. One thing that I didn't hear you mention was that water doesn't compress, air does. You can put pressure on water but not compress it like air can. So, the air on the suction cycle acts like a pillow.

[@piconano]

I love how they reused a tin can to make the hull. Clever recycling. The glass boiler made of chemistry test tube didn't do it justice, since glass is a good insulator. It brought back memories from when I was 6-7

[@Tim.Reader]

This reminds me of Feynman’s thought experiment of what would happen to the motion of the arms of one of those rotating (“helicopter”) sprinklers if it were placed underwater and sucked water in instead of expelling it out. Would it rotate in the same direction as the expulsion case, the opposite direction, or not at all?

[@hollt693]

I wouldn't think the spring loaded diverter arm that drives the rotation would move much (if at all) if water was being sucked into the spray aperture, but I can't say that I have anything more than intuition to base that on. Am I close?

[@charlieangkor8649]

It could also sometimes rotate this way sometimes that way or not at all. If we do a similar experiment - drain a sink and ask "will the water rotate or not and which way?", it may rotate every time a different way or not at all.

[@samroyston7281]

@@charlieangkor8649 that's the opposite of a scientific answer, congratulations. Feynman's ghost is probably doing backflips and it's not even true, water drains in a remarkablely consistent direction based on your hemisphere, an observation that has helped us deduce things about gravity and fluid dynamics. If we had just said "sometimes it does one thing and sometimes it does another", we havent observed anything, we've ignored reality

[@Mister_Brown]

not at all by my account for two reasons, one the force of the water coming in at a right angle hitting the back of the tube would cancel the suction "force" (i know, i know) but the main reason is those sprinklers use hydrodynamic bearings that float on a film of water provided by the hose pressure and seize up if you don't have pressure pushing up on the arms, even worse in suction

[@bobafettjr85]

@@hollt693 I think you're thinking of a different type of sprinkler. The helicopter type doesn't have a spring.

[@timus545]

Love the "transparent version" of everything. Understood engine working from transparent engine from SmarterEveryDay channel. It's make me understand concept, always knew how engine works but never felt from inside. This is also very beautiful.

[@tombig4011]

My dad and I built one of these for a science fair in 2nd grade. Won the fair and blew the teachers and judge away. We used coiled copper wire instead of a tank.

[@mr_dillus]

Lies

[@liahansen6896]

huh, do you remember how that worked with the wire? Like did you use the wire to essentially make a tank, or something else?

[@tombig4011]

@@liahansen6896 sorry, it was small copper tube the we bent into a coil that the flame heated. Not wire.

[@dpidcoe]

I feel like this explanation was lacking the usual rigor of explanations in previous videos, and it raised more questions than it answered: - What about a symmetrical boat with the same amount of water resistance forward as backward? - What if you pointed the tubes forwards? - What if the underwater portion of the tube had a T-junction with a one-way valve so that it would suck water in from the front and push water out the back?

[@NareshSinghOctagon]

Time to hire more glass boat makers,eh?

[@prophetsspaceengineering2913]

Agreed. I could definitely see asymmetric resistance being a significant factor. Hard to tell how much of the motion can be attributed to it.

[@enaudeni]

Symmetry of the boat aids the forwards motion but to a minor degree, if the boat was square it would still move in the opposite direction of the tubes. It comes down to the characteristics of the suction vs expulsion of liquid from those tubes. On the suction of the liquid, it sucks water in from an omnidirectional area. Yet when it expels the water it is in a directional / concentrated stream, like when you squirt water from a syringe it is in a long directional stream. So the expulsion of the water has a greater directional force than the suction so will always move in one direction far more than the other.

[@andrewfleenor7459]

I like the one way valve idea. Maybe a Tesla valve or two.

[@dave7038]

Explanations like in the video are pointless without experimental proof clearly demonstrating in isolation a 'wrong' explanation failing while the 'right' explanation succeeds. Otherwise the explainer could equally well describe a mechanism involving magical fairies that just like it when the boat moves 'forward'. That's why the ball-chain fountain series was interesting and educational. This was half-assed (maybe because Steve wants some other KZbinrs to call him out on it so they can do some response videos that get more engagement, much like Derek's recent electricity video (which IMO was specifically designed to be 'wrong' in ways that generate responses (see his other videos on clickbait and experiments with video titles that maximize engagement) that generated a great deal of traffic and engagement across several channels, much more than if they just posted a single correct, well-researched video).

[@thundernargundkar9618]

I remember when me and my dad would make these out of old soda cans. We would have to buy pre-made tubes and tanks but it was still fun. He said that these were a very common toy in India and other places in Asia

[@ApoorvPadhye]

This video unlocked a core memory for me as a child. I remember my dad bringing such boats from a regional fair nearby the city and showing me how it works. I wasn't allowed to touch it as I was very small and the boat used to be hot from recent usage. They went away as I grew up and I subsequently forgot about them until now.

[@Fernando_S]

I still have my dad's pop pop boat from the 1950's. It was his toy as a child. And it still works very well. Nowadays, my two 5 year old boys are the ones that play with it.

[@viplovchauhan1896]

Thanks!

[@infpail7232]

I bet the shape of the boat helps too. Since there’s more drag when the boat is accelerated backwards, it will have a slight preference to move forwards with the periodic motion from the tubes. Could be worth building a setup where the tubes are mounted in reverse to see if the drag being different is dominant over the argument you made for the collision between water and air. Great Job on the video! Edit: I said it was the first video I’ve seen on this channel. Turns out that was a lie. You got a new sub today

[@quartercast]

I agree. Movement is due to the streamlined shape of the boat. Same as the biased shape of the toothbrush bristles leading to forward motion of the bristlebot. I'm also not convinced with his first argument that jetting does not have an effect, I believe it would have an effect, regardless of conservation of mass in the reciprocating volume of water.

[@Dino14345]

If you move side to side on a small sailboat, you will go forward

[@marcfruchtman9473]

Thank you for the transparent view. I found it to be very helpful in explaining the oscillation of the liquid and how far the liquid actually travels back toward the tank. (As others have mentioned, the dye was also very helpful!)

[@NFMorley]

Really interesting - Thanks Steve. I remember playing with these with my grandpa as a little kid in the park beside their house! I think he did explain to me at the time how it worked, but all I'd ever remembered was that it was a bit similar to a Sterling Engine, so nice to see a clear model in action.

[@sukyoungkwon5784]

재밌게 상세한 설명 감사합니다.(62년생인데...어렸을때 마당에다 큰고무통에 물에띄어 신기해하며 놀랐던 추억이 생각나요)

[@SnahLhug]

I would love to see these two boats with a high speed infrared camera. This way we could also have a look at how temperature oscillates.

[@greenaum]

I would guess it hovers around 100C very closely. The latent heat of boiling / condensing is quite a lot, and while that's going on, over and over, there isn't enough energy moving either way to let the temperature change much. I wonder how big you could build a pop pop boat? Would a really big one work? I would guess either "no", or "you'd need a nuclear reactor".

[@The-KP]

High speed infrared camera, OR a fast thermochromic dye, one that activates at near 100C and beyond. Either would provide an experimental dataset to help push beyond the thought experiments provided in this excellent video.

[@JordanSchaeffer]

I used to make bristle bots all the time as a kid and something that is really important is that the bristles are all angled in the same direction. That ensures that it is depressed forward when it vibrates before the bristles spring back to their original position with the brush slightly moved from where it was before

[@matthewbarrowcliffe1091]

I think you missed something… the shape of the boat. I would like to see the test done with a rectangular boat to see if the lack of a bow makes a difference.

[@SteveMould]

I cut that from the video actually! I wasn't sure if it would interest everyone. But yeah, I think it probably enhances the effect.

[@matthewbarrowcliffe1091]

@@SteveMould my curiosity is about whether or not the pipe exiting the bow would allow the effect to be reversed, perhaps not efficiently. I may build myself a couple to experiment.

[@JCisHere778]

I don't think the shape of the boat will have that much of an effect. Most energy will probably not be dissipated through friction but through the surface waves

[@WJS774]

@@SteveMould Cutting that was probably a mistake, I swear like half the comments here are some variation of "you're wrong, it's actually the shape of the boat".

[@jele38]

Now imagine doing this with a full scale boat

[@FrogEmpress]

Just like in ponyo!

[@TTHJJD100]

Well the issue here with the pop pop boat is you still need heat that causes this process. Thus you still need a fuel like coal, gas, or wood. So we're back at the problem of needing a finite resource.

[@JustRememberWhoYoureWorkingFor]

It would be a very slow and inefficient boat

[@michaeldougherty6036]

@@JustRememberWhoYoureWorkingFor But at least you wouldn't be slap-chopping manatees and whales with a propeller. I wonder how well a solar powered heating filament could work, in place of a flame. I'm sure there could be a market for an environmental and sealife friendly put-put boat.

[@bconroy328]

Ponyo!!!!!!!

[@DJTI99]

Theoretically, how large could you make a pop-pop boat and still have it work?

[@DragonFiesta]

this is what I want to know aswell

[@_Matchu]

as big as my p... house

[@thomasbarlow4223]

Here come the new latest and greatest winter boats all over Wisconsin

[@ChickenDeranged]

ha ha, the answer to this is in a movie called Ponyo... lol

[@Aquanorte]

At least as big as titanic .. it had a similar working principle

[@jaronjohnson4366]

This is really cool! I just rewatched Ponyo and, towards the end, the main character's little boat (which I now is a poppop boat lol) gets made big enough for him to ride as a method transport. So I wonder how big a poppop boat could actually be 😂

[@sethkeown5965]

i didnt and havent wanted to watch ponyo. can you sell me to watch it?

[@SovietMarmalade]

@@sethkeown5965 what??

[@sethkeown5965]

@@SovietMarmalade ive bot seen ponyo, i want to hear a sells pitch that will get me to watch it.

[@a1esandra]

@@sethkeown5965 underwater town fantasy and the satisfaction of seeing a working Lifesize toy boat :3

[@a1esandra]

Right I've never seen this toy before but when it showed in ponyo I was so fascinated I'm so glad this video conveniently showed up on my feed

[@1.4142]

The first explanation is somewhat correct. After the first exhaust phase, water is sent backwards while the boat is propelled forwards, conserving momentum. When the boat draws in water a second time, it doesn't come from water used back in the first cycle, but local water ahead of the first cycle. In this sense, it's like climbing a ladder.

[@blackmber]

Ooh nice analogy.

[@megamaser]

Bingo

[@emersonpage5384]

that's interesting, because if true it would mean if he continued running the experiment with colored water inside the tubes, eventually the tubes would be filled with only clear water.

[@DaP84]

It should cancel out the energy/momentum regardless? When you push on something there is an equal and opposite force acting on you = how the boat starts moving. The same, but opposite physics phenomena should happen when the boat pulls water back into the pipe, regardless of which water it sucks in. So why doesn't these two opposite forces cancel out each other? So the analogy of climbing a ladder with your claim of "intake of local water" goes against basic physics. Must be some other factor that does it

[@1.4142]

@@DaP84 The key to the answer is the center of mass of the boat-water system. After the first cycle, if the boat were to draw back in the water expelled from the first propulsion, it would go back to its initial position. But by using local water ahead of the first, the center of mass of the boat-water system has moved forward.

[@danielescobar7618]

Never have even heard of pop pop boats. Amazing

[@itsawonderfullife4802]

The first explanation of how the propulsion works was actually quite right and also more easily understood using conservation of momentum. He didn't realize it (and was too dismissive of the first explanation) but his own (second) explanation was also a different version of the same first explanation. Remember, the initial momentum of the system (water-tank plus the boat) was zero and so (by conservation of momentum) it must remain zero at all times: 1. During the exhaust phase, collimated water clearly flows backward (along a single direction in 3D) and so the boat must glide forward (to conserve momentum: the two momenta sum to zero) and thus the boat receives a net momentum forward (water-tank plus the boat still has zero momentum). 2. In the suction phase, the inward rushing water comes from all directions and so the boat does not receive a net momentum in any particular direction (various momenta all sum to zero again but because the water on the whole has zero net momentum (rushing in from nearly all directions) the boat does not receive any net momentum either). 3. But it matters not, because the net momentum received during the exhaust phase is enough to propel the boat forward. NOTE much more than the various speeds (magnitude of velocities; Of the water molecules and the boat), it is the direction of various velocities that matters most.

[@jeffreylebowski4927]

But the water rushing in has to ultimatly assume the momentum that the direction of the pipes demand - even if the water is sourced from all around the pipe opening in the beginning, for it to be able to flow into and along the pipe it will need to get collimated anyways... it doesnt really matter how long the column expands outside of the pipes, within the pipes the water is a column and is streamlined.

[@megamaser]

@@jeffreylebowski4927 the water outside the pipe absolutely does matter because it affects the pressure on the boat which is another way to analyze this problem. But conservation of momentum also works. You just have to consider momentum of the entire system including the water outside

[@dominicread797]

Momentum isn't conserved because you are adding energy to the system. Without the candle the momentum would remain at zero.

[@megamaser]

@@dominicread797 Momentum is always conserved! Doing work doesn't change this

[@maxwang956]

@@dominicread797 Momentum is not energy. Momentum is conserved even in situations where energy is not. Backwards momentum generated by the boat is absorbed by the water and it's container, the same way that backwards momentum you generate while walking is absorbed by the earth. The change is negligible because of the difference in mass.

[@mrmaniac3]

Man, these are giving me visions of full scale, and even giant vehicles operating with these kinds of propulsion systems, perhaps in the style of those in classic Ghibli films. Imagine hopping on the pop-pop boat to be ferried across the channel to the opposite coast, at the edge of the desert where you catch a ride on a bristle bot for the trip to the oasis in the center

[@clownsabound]

there actually was a life sized pop-pop boat in a ghibli film called ponyo! its the reason why i clicked on this video funnily enough 😅

[@coloradolove7957]

Let's keep working on this....

[@ennoshita7495]

@@clownsabound same :)

[@MarkStiles]

This seems similar to those u-shaped pulse jet engines, though they typically mount the combuster on one of the pipes and one acts as an intake while the other is the exhaust but the noise produced is effectively the same resonance effect

[@tjtotheb]

this was my favorite little treat as a child when I’d go to the model train expo with my father and brother. Thank you for bringing back a great memory

[@sofiarocha9907]

When I watched Ponyo last year, I has a slightly different theory on how those work so it's nice to have it all laid out like this

[@codegeek98]

🤔 I don't remember those I will take this excuse to rewatch it

[@The2x4]

Very interesting & well made as usual! I don't quite accept the "collision" on the intake being that important of a factor for moving forward (and having no "anti-collision" on the output.) Just like the oscillating syringe example, the pressure and vacuum forces both slow and stop the motion, then reverse it, with seemingly equal force.

[@tau9632]

Exactly!

[@enderyu]

Why would you assume equal forces? You are grabing mostly still water around the boat and throwing it backwards creating net thrust. The ejected water will inevitably mix with the surroundings, and the still water around it will present less resistance and thus will end up being sucked into the boat, instead of somehow being ignored and forcing the boat to suck the same water it just spat out

[@maxwang956]

"Just like the oscillating syringe example, the pressure and vacuum forces both slow and stop the motion, then reverse it, with seemingly equal force." You're missing one thing: when the vacuum forces stop/slow the outward motion, there is less water in the tubes than during the reverse motion, because some of the water was pushed out!

[@RaccoonHenry]

that transparent boat is beautiful! and as a Ponyo fan this might be my favorite of your videos so far!!

[@siriusmywaifu4043]

This does put a smile on my face. 😊

[@wizardozark2735]

A mechanic you failed to mention about the metal pop pop boat is the top piece of metal in the chamber pops in and out just a little bit. This assists the positive and negative flows of the water. That's one of the reasons the metal one moved faster. Weight is likely a factor as well I'm sure.

[@_..-.._..-.._]

He mentioned that, maybe not that throughly, but it was said.

[@AabhasLall]

This was and still is my favourite toy! I always wondered why they don't use this kind of tech to power actual boats. Effeciency, perhaps? I would love to see some madlad making a huge boat which uses spent nuclear fuel to push boats around. Popping sound optional. Or something similarly bonkers yet fun.

[@raghubharadwaj7122]

spent nuclear fuel on regular boats 😂 noice

[@Nineninetails]

I was right there with you until you said spent nuclear fuel. The spent rods dont put out much to any heat. That is why they are considered spent even though they are still radioactive.

[@aquafyre99]

This exact concept was mentioned very briefly in the Harry Harrison Stainless Steel Rat sci-fi series. Not spent fuel, but a small nuclear source, as a simple, reliable backwoods boat engine.

[@AabhasLall]

@@Nineninetails Ah, interesting. I just knew that spent rods are to be placed in cooling ponds for 5-8 years. But nuclear powered popping boats sound nice, both conceptually and literally! :D

[@radadadadee]

Not sure how you can you stop the boat with nuclear rods

[@crow2250]

Ah I remember watching ponyo as a little kid, and up until now I thought that maybe the boat they used existed to some extent, but I never thought it would be exactly as theovie portrayed it, very nice!

[@SurajGrewal]

With? You never had one as a kid?

[@rickus7843]

Ponyo!! Was my first thought!

[@hk372]

The only thing I knew about these boats was that they were in that ghibli movie Ponyo, and I've always wanted to know how they worked, thanks for this!

[@observingrogue7652]

I'm here from your life size poppop boat video. All this reminds me of Colin Furze's pulse jet bike.

[@khalilahd.]

I love that I never know what I’m going to learn about when you upload a video 💛 it’s always a surprise and yet I’m never disappointed 😅

[@michaegi4717]

I'm not fully convinced about the expleantion how the movement of the boat happens. You forgot to mention that the exhausted water (outside boat) has much higher speed than the inhaled water (due to same direction) outside of boat. This shall result in a positive momentum over time, right? Did someone try to build a symmetrical pop-pop-boat, does this really not go forward?

[@jwhite5008]

Also not convinced. I think it's possible that the "exhale" momentum is greater because swift unidirectional water jet is more laminar and so travels farther and transfers momentum deeper and thus better to the entire water tub, whereas slower and less directional suction is more turbulent so sum of momentum vector is not necessarily the opposite of the pipe. Kind of like if you have a reversible vacuum cleaner, you can blow stuff faaar away easily in reverse mode, but it's relatively harder to suck stuff that is not in immediate proximity of the end of the vacuum tube.

[@MarcusHawksley]

@@jwhite5008 the explanation makes sense and balances the intake forces against the cessation of intake. However I would have thought that the jet of water Vs suction would also contribute to movement, could this also be the opposite of the intake, where the water mass is not stopped by the boat, leaving the boat with forward momentum?. I would like to see some measurements taken with accelerometers and of the magnitude of the exhaust. I'd also like to see the numbers for the momentum of the water in the tube. However I am lazy and hopefully someone else will do it and KZbin will show it to me.

[@nirodper]

yeah his first explanation was right. The same happens on a ventilation fan: the exhaust side is collimated and directional as the air particles travel due to the momentum transfered so it reaches long distances, while the intake side isn't as the air particles travel due to a difference in pressure so you can't feel the airflow if you're not right next to it. If the momentum was the same the boat would stop between pulses

[@timotay22]

I second your thought! Due to Helmholtz vorticity equation, an approximately inviscid flow that starts with no vorticity can create no vorticity, and impart no net force to objects surrounded by that flow. Sucking flows in a high Reynolds number regime (i.e. this put put boat) don't create this vorticity, so no net force arises. (Similar, but more rigorous argument to Steve's "sucking from all directions" argument.) That's why you don't feel much when you stand on the sucking side of a fan. Alternatively, blowing imparts a ton of vorticity to the surroundings (equivalent to Steve's "columnar" description of the outlet jet). So the outflow does generate a force on the boat. For a similar phenomenon, look at the "Feynman sprinkler."

[@SwoopWoW]

Yea, that explanation is incorrect. Momentum is mass x velocity. Mass stays the same, but velocity of the expelled water is higher. When you suck in the water the pressure difference can be at most 1 bar. (=vacuum in tank) When you expel the water the pressure in the tank can be much higher though, leading to higher exhaust velocity and thus forward thrust. Same principle as the thrust reverser on a jet engine.

[@FogyArts]

I remember seeing this toy in the movie Ponyo and I always wondered how it worked.

[@vikramadityasaini]

Thanks for the explanation, however i had never filled my pop boat with water, just light it under see the magic. In fact we used to light it in air and once lit place the boat in water, it's easier to light the thing while firmly holding in hand rather than dancing in water

[@AG-pm3tc]

I never heard of scientific glass blowing team, that sounds like the strangest hobby ever, but the really made something pretty

[@explosiverift2037]

Labs have them sometimes.

[@DocBree13]

It’s also a career, for some

[@johnmf6096]

My BIL is a scientific glassblower by trade and it IS in fact a career.

[@AG-pm3tc]

@@johnmf6096 can you tell us a bit more? what use cases employ your ability? how you got into it?

[@5naxalotl]

lab glassware is traditionally hugely expensive and large universities often have a glass blower who can do repairs, when it's not an item that can be mass manufactured in china there are a whole bunch of youtube videos of lab glass blowing. it's exactly as amazing as you'd think it is so you really should check them out

[@arktom7335]

Your videos are always the best💯 I do receive a notification each time you post a new video.. We'll have regrets for things we did not participate in...Investment should always be on any creative man's heart for success in life.

[@HLO-iy2bp]

Agree with you digital currencies that were once viewed as mysterious by many in the past went sky high making millions of dollars for a lot of people including I. It'll definitely do that soon

[@betheluktu7647]

I wanted to invest more in crypto, but the fluctuations in crypto value discouraged me into dumping.

[@philip1258]

@@betheluktu7647 Crypto trading is the best investment anyone could get into. As it could make you rich in a blink of an eye, trading with an expert is the only key to successful trading

[@georgebasonathan4784]

I have heard a lot about investments with Mr Arjun B Jagat and how good is he, please how safe are the profits?

[@charles2395]

@@georgebasonathan4784 Investing in crypto as a newbie was very difficult due to lack of experience which resulted in losing my funds.....but Sir Arjun B Jagat restored my hope

[@Tacospaceman]

I knew it. I’m so glad you’re doing this video rn dude. These were one of my favorite toys to play with. And the movie ponyo really made me love them

[@Lgg130]

I wonder how a large scale version would behave in the sea. Massive oscillation plus noise should make for a nice trip to the Maldives.

[@JustRememberWhoYoureWorkingFor]

It would be very inefficient

[@Kahsimiah]

The hydrodynamic shape of the boat helps in going forwards, instead of backwards, too. The bow has very little resistance, whereas the stern is pretty much a flat surface, increasing the resistance to make a backwards motion.

[@Boris_V]

How would it ever go backwards if it's propelled at the back?! The shape of the boat helps it go forward instead of in circles.

[@Kahsimiah]

@@Boris_V please watch 0:55 - 1:25 again. The water is pushed out, as it heats up at the top and becomes steam. But the steam gets cooled down by the pipes and collapses, becoming water again, so the same amount of water is being sucked in again. So there is some propelling going on, but also a reversed, negative motion, which would significantly weaken the forward motion, if the bow and stern were equally shaped. Now I didn't say the boat could move backwards, but shaped like it is, it will be a lot faster than a boat with an eqally hydrodynamic bow and stern. By making the boat more hydrodynamic in the front and as little hydrodynamic as possible in the back, it will always go forwards easier than backwards, helping the little motor picking up speed.

[@Leonardokite]

When you did your bird whistle video I bought some on Amazon and then I saw a video where a guy had a bunch of 3D printed whistles and that was one of them. I then 3D printed my own warbling bird whistle. My grandkids love them!

[@SteveMould]

Cool!

[@DaveVelo1]

Hmm, I think you're missing a crucial part of the boiler. That would be a spring steel plate used in clicker toys fitted to the top of the boiler. When pressure builds inside the boiler, it causes the steel spring to bend (click) into another position expanding the space within thus pulling cool water in. Pressure then decreases, the clicker returns to it's natural state forcing water out the tube.

[@hereiam2005]

The glass chamber does not have any such mechanism yet works just fine.

[@DaveVelo1]

@@hereiam2005 Not really.

[@hwgusn]

The glass one is cool, but I also like the little flutter of the metal one on the top.

[@CoolAsFreya]

The explanation I was always given as a kid was that the water came in one pipe and out the other, but that never made sense to me! Thanks for revealing the real mechanism!

[@anders8347]

Damn, what an interesting vid and mechanism, but I do have a quick question. Would air in the tubes cause the boat to travel at a different speed compared to when the tubes are completely filled with water?

[@pleasedontwatchthese9593]

I wonder if the tub water was colder if it would change its speed

[@josep43767]

@@pleasedontwatchthese9593 I assume colder water or hotter reservoir would increase the speed since there's a bigger energy difference. At least a Stirling heat engine works this way.

[@AlbertaGeek]

Good point. I was also thinking that the air-to-water ratio in the tank played a significant part. Perhaps further experimentation is needed.

[@benzina5917]

I remember playing with these as a kid and my Dad made me one out of brass. Wonderful memories and I'm going to call my parents now :)

[@Jasonrotfl]

I built one when I was a kid out of thin galanized steel and a coil of thin copper tube I got at a hobby store. Was really heavy but worked suprisingly well with a sterno can heating the coil.

[@nsmith0723]

I think it's the same effect as blowing a small flame out with a phone speaker. Even though the speaker both pushes and pulls, the net effect if stronger in one direction

[@GeorgeWBush-gx3zy]

This is a big ask but I think it's something right up your ally that you'd love to dive into. Could you make a video on supercavitation or just cavitation in general. Supercavitating projectiles and torpedoes have always been a huge fascination of mine and its a relatively new technology so there is lots to learn :)

[@spddiesel]

The original boat tank is very thin, about the same thickness as the pipe, compared to your glass one. This may make it easier to push out more air, especially if one tube extended all the way to the back of the tank.

[@agniveshF]

Also something as simple as the shape of the boat where the front allows for less water resistance vs the back of the boat would contribute to the impulse (change in momentum) to forward motion, even in the hypothetical condition that the forces cancelled each other out

[@Alexmaystudio]

Thanks for making this video. My grandad made a boat like this for me and I was a little too young to remember his explanation of how it worked. He was an engineer at Marconi and even made his own TV before anyone else in his town had one. Needless to say the boat was a work of art.

[@gamertherapyconsoleyoursel5804]

I'd love to see this tested across different hull designs to prove the resonance theory.

[@Mrugendraa]

A simple explanation by me🙃🙃🙃: it produces just back and forwards oscillations, and the main reason which pushes the boat forwards is ---> 1) the watter coming out of the end of both tubes goes straight direction i.e. 180⁰ angle only (becauseof momentumof water) , so it creates the much pressure which propells the boat forwards, but 2) while the contraction cycle the water gets sucked in but this water comes in not in straight direction, it comes from all direction of the both ends of the tubes , (in least resistant way) so the pullback force is less for 180⁰ angle as the force is diveded on other angles i.e. sideways. that difference between forward and backward pull forces makes boat to travel in forward direction. its like vacuum cleaner motor needs more energy to suck 1kg mass from a large distance. but blower motor consuming same energy can propell the same 1kg weight from same larger distance easily.

[@ArunNalluri]

i had this when i was a small child here in India, i always thought it pulled water in from one tube and pushed it out of the other, great video!

[@incandescentfennec6916]

I'd love to see if/how this engine works on something of a more practical size, imagine a rideable pop-pop boat!!

[@axuwu6939]

Same!! Mostly I just want to know if that one scene in Ponyo would be possible

[@BrentBestwick]

I was hoping for some additional discussion / experimentation about how to change the resonance frequency (water/air proportion? exhaust tube length?) and the resulting effect on boat speed. Also, the glass blowing was indeed phenomenal.

[@5naxalotl]

i think the issue there is that nobody really designs in the resonant frequency. whatever geometry you choose, the system will find a resonant frequency that couples the energy into eficient fluid motion. even the flexible steel membrane that people often describe as an oscillator isn't actually tuned ... it's supplying a non-linear effect that would function in oscillators with a range of frequencies. imo it's an interesting question, but poorly studied since tinkerers can get the result they want with trial and error

[@Sam_Chintapalli]

0:14 "this channel is becoming a transparent version of things" lol 🤣🤣🤣😂😂😂

[@BobClemintime]

Not convinced by the “collision” theory for propulsion. May make more sense thinking about how some of the energy from the sucking moment goes into compressing the gas, which doesn’t happen on the push stroke since water is relatively incompressible. But I think the asymmetric drag resistance of the boat may be important

[@SmDJeremy]

Relatively incompressible? I'd say incompressible. :p I'm betting the shape/size of the tank makes all the difference.

[@pedrosmith221]

5:20, every time I light a candle I see that movement of a particle going really fast towards the wick and getting expelled over and over. You could explain that in another video!

[@Leptons_]

To anyone who can't see what this comment is talking about, it's in the *bottom left corner* of the screen. There's a small black spot floating in the molten wax of the candle.

[@kain0m]

That's just the convection of the molten candle wax becoming visible because there is a particle floating in it. The wick is hot, also the wax near it is being heated by the flame. The hot wax rises to the surface (due to lower demsity), drawing cooler wax along with it. That results in the hot wax being pushed outside, where it cools down and sinks again.

[@marcin_szczurowski]

"During the expulsion phase, there's no cancellation of momentum (...)" Actually, during the suction phase, when water going into the tubes, it eventually stops because of higher gas pressure inside the tank. But during the expulsion phase, water is stopped by the pressure in the tank being lower, which pulls in water inside. I see these as more or less symmetric and I think the first explanation is what's actually happening.

[@maxwang956]

"But during the expulsion phase, water is stopped by the pressure in the tank being lower, which pulls in water inside." The asymmetry here is that there is LESS water to be stopped in this phase than the other one, the column of water is shorter after some of the water was expelled.

[@marcin_szczurowski]

@@maxwang956 You get the same amount of water going through pipes outlet both ways. Pressure is a force over pipes cross-section. The latter one doesn't change, but the force oscillates along the pipe axis. Or, translating it to thought experiment, let's assume a long tube with some section in the middle filled with water. It water will oscillate inside, the tube will vibrate in its axis of rotation, but not move forward. Pressure / force-wise, this looks like a closed system. For propulsion there needs to be some kind of interaction with environment. For rockets we lose mass. In case of that boat, mass remains unchanged, so the interaction with surrounding environment have to look different. The first explanation take advantage of roughly isotropic suction and anisotropic exhaust. in a couple of oscillation cycles, water from around the pipe is being pushed behind the pipe, and moving mass uses force. Like a rocket thet sucks air from sides and expels it through the engine.

[@maxwang956]

@@marcin_szczurowski The boat looses mass during the out-take and gains it during intake, the forces in these two processes are not symmetric.

[@nicoracien1924]

Use to do big offgrid parties and we were warming up a big pool with a 45gallons steel drum, using this theory. We call it the popcorn heater

[@TKTrooper]

Such a brilliant glass model. I wish it was an available item to buy

[@gaylebordeaux7632]

It was sold as a toy in early 50’s, they sold for about 85 cents, produced by Japan. When my son was 6 years of age, about 1976 I built one. He so enjoyed it he has it today. The boat was built with a coffee can and copper tube, more fun to build then to play with. Give it a try!

[@kriskeersmaekers233]

I'm not convinced about the forward motion explenation. Can you make a model with plastic tubes that you can reverse?

[@microwaveoven9170]

I was wondering why the pop-pop boat was so familiar, and then I realized it's the same one from Ponyo, and I've always wondered with mechanics behind it were.

[@siriusmywaifu4043]

Same. 😂

[@sk-sm9sh]

I feel like I wasted my life. I had lived bit over 30 years and had never ever heard or seen of pop-pop boats. This has saved me. Now I know what is pop-pop, how it works and I even know that pop-up boats made from glass don't make pop sounds. Thank you

[@afandianto]

I remember my parent give this at my childhood Btw in indonesia we call it "kapal otok-otok"

[@irchonite1953]

that's so cool! :)

[@Caio0365]

When you were explaining why the boat doesn't reverse due to the reciprocating motion, the first thing that crossed my mind was the shape of the boat. It's pointy in the front and all squared in the back, so it takes more energy to reverse then to go forwards, so it ends up only going forwards due to the momentum and water resistance combined.