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Pop-Pop Boats Are Weirder Than You Think

  • Published on Sep 24, 2023 verΓΆffentlicht
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    I got a glass pop-pop boat made (or putt-putt boat, or a Ponyo boat!) to see once and for all what's going on inside!
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Comments • 0

  • Steve Mould
    Steve Mould  Year ago +2386

    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
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    • Sixten Widlund
      Sixten Widlund Year ago +11

      Nice video!

    • Robert Schnobert
      Robert Schnobert Year ago +11

      I love you, Steve! 🌈

    • khadim husen
      khadim husen Year ago +4

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

    • Little Bacchus
      Little Bacchus Year ago +12

      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
      nobody Year ago +10

      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
    arbitraryconfusion Year ago +7513

    Those glassmakers did an incredible job.

    • Freid Leming, Worlds Rootin'est Tootin'est Milkman
      Freid Leming, Worlds Rootin'est Tootin'est Milkman Year ago +146

      probably the most notoriety they've ever had

    • PleaseDontWatchThese
      PleaseDontWatchThese Year ago +140

      i would like a video seeing how they made it

    • Schnizzyfizz
      Schnizzyfizz Year ago +72

      @PleaseDontWatchThese 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.

    • Anthony Nelson
      Anthony Nelson Year ago +47

      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.

    • Comrade Garrett
      Comrade Garrett Year ago +46

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

  • Myster
    Myster Year ago +93

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

    • A random youtuber
      A random youtuber Year ago


    • Sirius My waifu
      Sirius My waifu Year ago

      Hehe~ There are more of us...

    • Plurmple
      Plurmple Month ago

      I LOVE ponyo

    • Carmelo Rodriguez
      Carmelo Rodriguez 28 days ago +2

      In 1952 I had a pop-pop boat and just thought that the way it worked was for the steam going out, just as a jet engine. Very interesting

    • Lagamerfuel96
      Lagamerfuel96 21 day ago

      I really want to drive a boat like the one from ponyo, that would just be so fun to boat around in a fire powered jet boat basically

  • Matthew Barncord
    Matthew Barncord 9 months ago +254

    for forward motion, the shape of the boat also acts as a latching/winching mechanism. It glides forward in the water easier than it glides backwards, due to the hull shape.

    • Craig Cole
      Craig Cole 9 months ago +13

      This is correct. You put a corner in the front of the boat, so it sluces easier. In the back of the boat is a wall, which absorbs energy. The greater area of the wall blocks the boat going backwards. It’s the same reason a man in a rowboat will expend WAY more energy rowing it backwards, rather than forwards.

    • Matthew Barncord
      Matthew Barncord 9 months ago +22

      @Craig Cole on the other hand, I've seen these boats made out of plain sardine cans, so there must be some net forward gain.

    • Dean Simmons
      Dean Simmons 9 months ago +2

      Well said guys! πŸ˜ŠπŸŒŽπŸ’–

    • Marco Pruscini
      Marco Pruscini 8 months ago +7

      Water on speed wants to stay in direction, here to the back, as long as it moves fast. Sucked water (or any other medium) tries to get the easiest and shortest way and that is every possible direction. That means, the reaktion force of the pressure water is forward and of the sucked water is in almost every direction and eleminates most of it by it self. May be the physical terms are not correct because of my non Oxford english...πŸ˜‰

    • GermΓ‘n ViΓ±ao
      GermΓ‘n ViΓ±ao 8 months ago +7

      That is correct but as he said, when the water is coming in the tube it has less velocity than when is going outside. If you answer me I can give you the fluid dynamic formula which models this phenomenon. You can see it when an octopus is running away, it takes water with its siphon wide open and then it makes his siphon smaller to take the water away and gain velocity.

  • Ken Karnes
    Ken Karnes Year ago +183

    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.

    • Blaise Bailey Finnegan
      Blaise Bailey Finnegan 9 months ago +10

      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.

    • Buck Fizzard
      Buck Fizzard 9 months ago +32

      @Blaise Bailey Finnegan why would you disrespect the man like that

    • Blaise Bailey Finnegan
      Blaise Bailey Finnegan 7 months ago +4

      @Buck Fizzard Because I can, homeboy.

    • Buck Fizzard
      Buck Fizzard 7 months ago +24

      @Blaise Bailey Finnegan well that's immature

    • Poize
      Poize 5 months ago +8

      Your grandchildren are so lucky. β˜ΊοΈβ˜ΊοΈπŸ‘πŸΌ

  • Sanjay
    Sanjay Year ago +66

    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
      EzioBoiz 10 months ago +1

      You should already know this because this is taught in physics πŸ’€

    • Dο½…monitο½…
      Dο½…monitο½… 10 months ago +2

      @EzioBoiz Not everyone learns the same things in school πŸ’€

    • EzioBoiz
      EzioBoiz 10 months ago

      @Dο½…monitο½… wait so you're 9 year old?

    • Dο½…monitο½…
      Dο½…monitο½… 10 months ago +2

      @EzioBoiz ?

    • EzioBoiz
      EzioBoiz 10 months ago

      @Dο½…monitο½… i mean the physics taught in this video is basic physics you're taught.

  • Jordan Schaeffer
    Jordan Schaeffer Year ago +14

    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

  • NightHawkInLight
    NightHawkInLight Year ago +625

    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?

    • Steve Mould
      Steve Mould  Year ago +164

      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 steve@stevemould.com

    • Little Jackalo
      Little Jackalo Year ago +33

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

    • Let's Talk Law
      Let's Talk Law Year ago +18

      @Little Jackalo The bot presence is strong on youtube

    • Resonanttheme
      Resonanttheme Year ago +6

      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.

  • Thunder Nargundkar
    Thunder Nargundkar Year ago +35

    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

    • Apoorv Padhye
      Apoorv Padhye 4 months ago +1

      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.

  • Harry F
    Harry F 6 months ago +4

    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.

  • Tom big
    Tom big 9 months ago +33

    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.

    • mrdillus
      mrdillus 4 months ago


    • Lia Hansen
      Lia Hansen 2 months ago

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

    • Tom big
      Tom big 2 months ago +1

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

  • Dave Sunhammer
    Dave Sunhammer 9 months ago +28

    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.

    • Harry Moyes
      Harry Moyes 2 days ago

      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.

  • Raymond Fagan
    Raymond Fagan Year ago +2

    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.

  • Andrew Smith-Thomas
    Andrew Smith-Thomas Year ago +1518

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

    • truong nguyen hong nhat
    • Leyrua
      Leyrua Year ago +7


    • Truth Be Told
      Truth Be Told Year ago +38

      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.

    • Hank Holschuh
      Hank Holschuh Year ago +19

      @truong nguyen hong nhat it was a joke genius

    • bstikkel
      bstikkel Year ago +7

      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.

  • Wizard Ozark
    Wizard Ozark 7 months ago +13

    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.

    • Mcroostr
      Mcroostr Month ago +1

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

  • collomps
    collomps 9 months ago +26

    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
      Layarion 8 months ago +2

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

    • Beacon Blaster
      Beacon Blaster 8 months ago +1

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

    • DethstruXioN β„’
      DethstruXioN β„’ 3 months ago +1

      @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.

  • Peppy Zacat
    Peppy Zacat Year ago +1

    I think the motion could be as well explained with the change in the center of mass. If you have 2 masses on a boat and you change their position, the center of mass will move, leading to the movement of the boat. If you do that repeatly, the shape of the boat will lead to a forward motion. It will be interesting to do this experiment with a pendulum on a boat.

  • nsmith0723
    nsmith0723 Year ago +4

    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

  • Steve Lawrie
    Steve Lawrie 5 months ago +3

    I used to collect put-put boats as a kid: the role played by the thin metal diaphragm is crucial

  • christianlange102
    christianlange102 2 months ago +1

    For the forward motion i have another theorie that could apply. If the water is pushed out the tube, it will take the surrounding particles with it. like if you blow in an empty bag from a distance, the bag fills quicker as if you press it on your mouth and blow it like a ballon. When the water gets sucked in, a smaller volume of water gets accelerated to get sucked back in the tube.

  • Sky Trembath
    Sky Trembath Year ago +20

    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.

    • Bence Joful
      Bence Joful Year ago +2

      That was my guess as well

    • DethstruXioN β„’
      DethstruXioN β„’ 3 months ago +1

      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.

  • Keep It Simple Idea Guy

    I would argue the bristle bot is not truly oscillating motion because of the rotary nature of the weight. The weight has a tendency to hop the bristle up and forward then down and backward which has a β€œhopping forward” effect. You can change the direction it hops by changing the direction of the motor. Great vid. Beautiful glass boat. That visual took so much speculation out of the equation. Two thumbs up

  • Hey Boomer
    Hey Boomer Year ago +2

    I had one of these as a child, but had completely forgotten about it. Thanks for the memory bump, and the explanation of how it works.

  • Eidolon
    Eidolon Year ago +1554

    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.

    • Khalilah D.
      Khalilah D. Year ago +28

      Yeah I definitely agree

    • Taras Datsiuk
      Taras Datsiuk Year ago +67

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

    • Archbox
      Archbox Year ago +146

      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?πŸ€”

    • Chorus of Oddities
      Chorus of Oddities Year ago +35

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

    • Benjamin Bugl
      Benjamin Bugl Year ago +62

      making a symmetrical boat would be interesting.

  • Henry Garrett
    Henry Garrett 8 months ago +3

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

  • SilntObsvr
    SilntObsvr Year ago +1

    I'm thinking this is equivalent in operation to the thermoacoustic engines I've seen -- the extreme form of which is known as a "howler tube" -- a hot mesh inside a tube open on one end, which will oscillate in audio frequencies (depending on the size of the tube). These operate like a Stirling engine without any mechanical displacer mechanism -- which appears to be a similar effect to what's happening in your see-through pop-pop engine.

  • Richard Bussell
    Richard Bussell Year ago +2

    Would an adjustable torch effect the frequency of the pops? If so it could possibly act like a speed control.

  • TheBoatroom
    TheBoatroom 6 months ago +1

    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

  • Jasonrotfl
    Jasonrotfl 10 months ago +1

    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.

  • PhantomSavage
    PhantomSavage Year ago +2302

    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.

    • James Dreger
      James Dreger Year ago +485

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

    • Amber Black
      Amber Black Year ago +185

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

    • flagmichael
      flagmichael Year ago +253

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

    • BeSquareOrBeThere
      BeSquareOrBeThere Year ago +91

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

    • mucia55
      mucia55 Year ago +68

      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.

  • Kaizer Mordecai
    Kaizer Mordecai 10 months ago +1

    Great explanation! Now for our next question: would be possible to make a life size, working pop-pop boat?

  • Abhishek Nadkarni
    Abhishek Nadkarni 5 months ago

    Played with this boat since my childhood. Always wondered how it actually works. Thanks a lot for this beautiful explanation!!

  • M R C C M R
    M R C C M R 9 months ago

    Never heard of pop-pop boats..but the propulsion part could ALSO be explained because the back of the boat is squared off resulting in more friction. I would love to see one with a more canoe shaped design.

  • Dicerson
    Dicerson 3 months ago +1

    That's a very interesting mechanism. I wonder how energy efficient it is- that is, for however much heat you're putting in, how much force is getting put onto that boat? Would an air-based mechanism work for a wheeled vehicle if everything was scaled up? I know jet engines suck in air and push it out the other way, and I know traditional combustion engines turn pistons using explosions that expand and recede (basically just a giga-fast version of this sort of phenomenon). But if you tried to do something like that directly with the fluid mass like the pop pop boat does just on a larger scale, does that actually work?

  • Dio
    Dio 10 months ago +3

    What I wanted to know is who came with the idea of the pop pop boat in first place and added a metal plate? The guy was a genius

  • Shami
    Shami Year ago +764

    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
      Laurpud Year ago +29

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

    • Rachelcookie321
      Rachelcookie321 Year ago +9

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

    • Shami
      Shami Year ago +45

      @Rachelcookie321 yeah, it's how sosuke and ponyo go around to look for his mom once the water rises

    • Rachelcookie321
      Rachelcookie321 Year ago +12

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

    • Korwynze
      Korwynze Year ago +36

      same i thought of Ponyo right away! ahh what nostalgia

  • Blaize m
    Blaize m Year ago +1

    I made these from plastic ketchup bottles and thin metal piping from the back of a old refrigerator when I was in grade 5 for a science fair project... The pop pop boat I made didn't actually have a "tank", I just made a coil in the center from the mental piping and used that as the "tank", I found 3 loops worked best. And because it was just basically one long metal straw, I just sucked one end of the pipe with the other end in the water to easily fill it...

  • Microwave Oven
    Microwave Oven Year ago +5

    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.

  • Kyle Miller
    Kyle Miller 10 months ago +1

    The shape of the boat will influence it's motion as well. For a typical V shaped haul, it's much easier to push the boat forward, as apposed to reverse.

  • avfusion
    avfusion 5 months ago +1

    I think the net forward direction has a much simpler answer: The boat's shape makes it easier to move forward than backwards. If the boat was, say, a circle, you'd see the boat scoot around everywhere but in one single direction.

  • Ever Weaver
    Ever Weaver 9 months ago +65

    Now imagine doing this with a full scale boat

    • Space Empress
      Space Empress 9 months ago +36

      Just like in ponyo!

    • TTHJJD100
      TTHJJD100 9 months ago +7

      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.

    • Just remember who you're working for
      Just remember who you're working for 9 months ago +3

      It would be a very slow and inefficient boat

    • Michael Dougherty
      Michael Dougherty 9 months ago +13

      @Just remember who you're working for 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
      Bconroy328 9 months ago +3


  • Jierda Stormcrow
    Jierda Stormcrow 5 months ago

    I had one of these as a kid and I was absolutely certain that it worked like a pulse get, sucking water in one pipe and pushing steam out the other. My boat wasn't terribly good so it went in circles, that may have contributed to my theory

  • Raymond Mejia
    Raymond Mejia Year ago +2

    cuando yo tenia aproximadamente 5 aΓ±os de edad , este era uno de los juguetes que mΓ‘s me fascinaban , incluso llegΓ³ a comprarme uno mi MamΓ‘ , y con el tiempo se descompuso , uno crece y no lo recuerda hasta que videos como estos nos traen de regreso estos recuerdos.......tal vez no sean originarios de MΓ©xico y hayan sido una copia de algun otro paΓ­s , pero yo ya tengo 68 aΓ±os de edad ......asΓ­ que hagan la cuenta.......muy bonitos.

  • scott colbern
    scott colbern Year ago +3

    I like how he even used a see through tooth brush in his bristle bot demonstration.

  • Erik T
    Erik T Year ago

    Not sure if it was asked or if I missed it in the video but couldn't the issue between the pop pop & your glass made (which was made flawlessly!), Wouldn't the heating element size be a factor?
    Would you need roughly double the heat for the glass boat due to the size of the tank?
    Does that matter in this case?
    Like you said, clearly the glass tank doesn't move & pop like the Pop Pop's does but I'd imagine the amount of heat it's receiving is considered

  • Heika
    Heika Year ago +265

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

    • I couldn't think of a good name
      I couldn't think of a good name Year ago +24

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

    • Educational Purposes Mostly
      Educational Purposes Mostly Year ago +2

      came here to say this

    • TheCookiePup
      TheCookiePup Year ago +34

      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.

    • PleaseDontWatchThese
      PleaseDontWatchThese Year ago +14

      @TheCookiePup maybe a lot of small engines

    • S R
      S R Year ago

      @PleaseDontWatchThese Great idea!

  • Angus MacKinnon
    Angus MacKinnon 5 months ago

    Hello Steve. I was delighted to find this podcast as I remember my dad buying my brother and I, each a put put boat with exactly the same little engine in it. This was back in 1954. The only difference was that instead of a little Tea Candle, we'd use Methylated spirits in the container. The little engine was filled exactly the same as you did, with water being injected into one of the pipes at the rear, and we knew the tank was filled when water squirted out of the pipe not being used to fill the little tank. As demonstrated in your video, the little tank was slightly sloped toward the outlets, and the little boat would scoot off as soon as the water got hot; with one difference. When it ran out of water in the tank; instead of sucking the water back in; the tank would empty and the solder that held the tank to the two outlet pipes simply fell off. There was no sucking in of water as the little thing motored along. Poor old dad made a rod for his back for after each "Maiden Voyage" if we did not grab hold of the boat and remove the small pan containing the metho, the "boiler" plate would fall off. I have been looking at making a little boat for all my grandsons who would love them.

  • Maximilian Walker
    Maximilian Walker Year ago +4

    Beautiful little glass boat those guys made! Though I do have an idea for a true recreation of the pop-pop boat that can have more of a way to deform. Using clear plastics similar to straws would help for the tubes/enclosed space, and making the boat itself out of the same or similar materials would help. Getting a heat-resistant plastic would also help with this as well, to make sure the flame doesn’t burn through the plastic. I think I know why you didn’t do this, since the plastics burning is uh t o x I c but it would be interesting to see one with a high melting point that wouldn’t produce too much toxic gas and smoke.

  • silversonic1
    silversonic1 10 months ago +1

    The shape of the the boat also helps it move forward. The aquadynamics are favorable for forward motion, as the front is in a more curved and arrowhead shape and the back is more squared. The more squared back can't move through water as easily as the curved front, so you can get more net motion forward than back.

  • Naveen Surya
    Naveen Surya Year ago +1

    This was my dream boat as a child.
    Now, I've almost understood how it worked.

  • Kmuzac
    Kmuzac Year ago +3

    I always thought that they worked because of the pop and that's sort of accurate. Water gets pushed out horizontally but the return pressure pushes against the popper vertically, allowing it to move forward. It's cool to see that it's just the air pocket though. Love the channel and this video made me a subscriber πŸ˜πŸ‘

  • RouxTheKitsune 3300
    RouxTheKitsune 3300 3 months ago

    I kinda knew how this worked back when I was a kid and watched "Ponyo"
    In the film, the kids had a pop-pop boat but it was huge
    One big enough to find two kids
    And they kinda showed how the thing worked
    They even had to get a new candle at one point to "refuel" the engine
    They had a little rudder to steer, and the temperature difference powered the engine
    It was a cool idea that makes mw want a man-sized Pop-pop boat to drive myself on the lake

  • Chorus of Oddities
    Chorus of Oddities Year ago +639

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

    • Khalilah D.
      Khalilah D. Year ago +3

      Always the best content πŸ’›

    • desu38
      desu38 Year ago +5

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

    • amicloud
      amicloud Year ago

      Better than "pour things out of jars" channel

    • desu38
      desu38 Year ago

      @amicloud Well, I like NileRed

  • juscoz customs
    juscoz customs 5 months ago

    Now I am curious to see how far this can be scaled. could it be made into a full size boat like in the movie Ponyo? or does this only work because the tubes are such a small diameter the water surface tension helps to keep the air inside?

  • Daniel Cascaddan
    Daniel Cascaddan 4 months ago

    Thank you for explaining that. I had never seen one of these boats and came across it a couple of days ago. I could not figure out how it works and another video basically said that it was magic, without actually using the word magic, which was highly frustrating. Now I have some understanding.

  • Bren Krasmer
    Bren Krasmer Year ago

    Another factor in the oscillating momentum leading to forward motion could be the design of the boat itself. The angled front has to put less effort into displacing water, whereas the flat back essentially provides a wall preventing backwards momentum, as the angle to displace is much greater than the front.

  • Liquid Audio
    Liquid Audio 10 months ago

    Fascinating, I was scratching my head pondering the dilemma of how it moved forward vs just back and forth. Very cool!

  • Ian Bruce
    Ian Bruce 10 months ago +1

    Thank you! I was always unsatisfied with the standard explanation! I was particularly delighted by the explanation of how the forward motion is caused--a crucial aspect that is totally ignored in the standard explanation.

  • JimFC Gregg
    JimFC Gregg Year ago +461

    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.

    • Alex G
      Alex G Year ago +24


    • Lastie
      Lastie Year ago +11

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

    • Abao the Great
      Abao the Great Year ago +2

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

    • Resin Tom
      Resin Tom Year ago +8

      @Abao the Great you’re fun at parties I bet.

    • Shawn S
      Shawn S Year ago +5

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

  • Andy Plays Games
    Andy Plays Games Year ago

    I'd be really interested to see a scaled up version of this. Maybe even normal boat sized with manual controls for direction, maybe even solar-powered electronics. That leads to the question: Could this be a sustainable method of normal boat travel? and What would the effects of expelling this heated water be on sea life and the health of the waterway in general if many many boats like this were being used?

  • Plumb Bob
    Plumb Bob 7 months ago

    They operate very similarly to a stirling engine. The column of water in the tubing is the piston that responds to the vapor expanding and contracting.

  • Colin McKenney
    Colin McKenney 10 months ago

    Most honest sponsorship/review out there. Love your videos and appreciate your approach to this.

  • Rich bob
    Rich bob 7 months ago

    It is such a pleasure to see science video on Clip-Share by someone who is actually very well educated for a change. I have had so many cannels I like end up going full sensationalism. Too many times channels like infographics (and the plethora of other ones from the same guy) just make stuff up and embellish. I am so sick of thinking I am learning something only to later find out it was all completely wrong. I feel like I can actually trust this channel because Steve is genuinely very intelligent and has a masters degree in physics from oxford which is about as good as it gets for education.
    Thanks Steve, keep up the fantastic work!

  • Happy Fox
    Happy Fox 4 months ago

    Cool video, played with one when I was a kid. Always wondered how it worked. Now, have you tried putting the boat in a bigger boat, to see that they don't move ?

  • Fabio Cavaliere
    Fabio Cavaliere Year ago +263

    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.

    • Nicolas Thorngage
      Nicolas Thorngage Year ago +4

      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)

    • bootylicious
      bootylicious Year ago +5

      ​@Nicolas Thorngage 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.

    • Mick , yet another one
      Mick , yet another one Year ago +2

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

    • Lucas Barbosa
      Lucas Barbosa Year ago

      @bootylicious 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.

  • JosΓ© Luis Cordova

    You know, we have to give credit to this man. What a great explanation for just wanting to hide the fact that the boat uses batteries to run

      GIRISH DHOND 10 months ago

      How to get the one, please reply

  • Alexander Lawson
    Alexander Lawson 10 months ago

    Something else that would help with the forward morion of the boat (vs reciprocation) is the shape of the body in the water. Aerodynamic in one direction and a bluff body in the other, reducing drag in the forward direction, and increasing it in the reverse.

  • Joe O
    Joe O 3 months ago

    I would like to see a version of this where the front and back of the boat are the same shape.
    I think forward goes because it's pointed and it's easier for the boat to move, but backwards it's up against a flat back and resists movement slightly more.

  • riks
    riks Year ago +1

    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

  • Dmitry Zinenko
    Dmitry Zinenko 11 months ago

    The moka pot has a very similar working principle to what's explained at the beginning of the video. I once thought that the coffee in it is extracted by steam, which then cools down and condenses in the upper chamber, but in fact it does not even have to reach the boiling point to work.

  • Fuddleton
    Fuddleton Year ago +175

    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.

    • ZPERO
      ZPERO Year ago +32

      Interesting πŸ€”
      Explain it again, but pretend I'm 15 😁

    • Case Closed
      Case Closed Year ago +11

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

    • unfaπŸ‡ΊπŸ‡¦
      unfaπŸ‡ΊπŸ‡¦ Year ago +5

      What is a bulk modulus?

    • Hjertrud Fiddlecock
      Hjertrud Fiddlecock Year ago +5

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

    • The Rising Dragon
      The Rising Dragon Year ago +14

      @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!
      EDIT: Also heat be important for good popping!

  • joemck85
    joemck85 Year ago

    Also consider that the boat is, well, boat-shaped. The pointy bow is more hydrodynamic than the flat stern. So when water is expelled from the tubes, it can move forward more easily than it can move backward when water is sucked back in.

  • Skarry, Terran Envoy to Star Pilot Alliance

    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.

  • scorellis
    scorellis Year ago

    It seems like one could construct something like this with closed tubes (they’d have to be quite long, I think) because radiant cooling. As long as there is more force in one direction than the other. A thing will move. For example, sitting in a boat with a shotgun braced against the forward wall, and an impenetrable target placed against the back of the boat, it should move the boat forward-there will always be more energy released from the barrel of a gun than goes into the kinetic energy of the bullet. If the boat is long enough, and the boat has an open surface, the energy of the bullet striking the back of the boat is negligible.

  • Zeng Wenxin
    Zeng Wenxin 5 months ago

    The oscillation always begins by pushing water. So within each push-suck cycle, the boat first pushes the water, gaining some momentum, then sucks the water back, losing that momentum. During this cycle the boat moves forward a little bit, like the brush head. At a higher frequency then it looks like moving forward continuously.

  • Sina Alex
    Sina Alex 5 months ago

    Thanks a lot for this scientific explanation of such a simple toy boat. In my opinion there is physics all around us every day and everywhere, and much more than we realize.
    I'm sure, later in life kids might regret some day, when they didn't pay attention during physics lessons.
    By the way, this Anker power station is great. I got one too. It's very useful for a camping weekend to power some lights or other stuff.

  • Colin Engebretsen
    Colin Engebretsen Year ago +126

    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
      DJZofPCB Year ago +6

      On the head of the nail.

    • Sebastian Woodard
      Sebastian Woodard Year ago +7

      man I love Clip-Share. you can learn so much stuff just by reading the comments

    • Sebastian Woodard
      Sebastian Woodard Year ago +1

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

    • David Martin
      David Martin Year ago +8

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

    • Altruism First
      Altruism First Year ago +8

      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.

  • Arnav Dixit
    Arnav Dixit Year ago +1

    I love how steve makes simple things complicated.
    Luv u steve πŸ’–

  • Doc Jackal
    Doc Jackal 9 months ago

    Great video. I used to play with them in my childhood and I was pretty intrigued how it worked. Thanks to you now I know. Might get a couple of pop pop boats to play with too πŸ€ͺ I also watched your entire advertisement of Anker.

  • Peter
    Peter 7 months ago

    Another interesting video. Thank you. With regards to converting reciprocating motion into forward motion, have you had a look at children's flicker scooter (e.g. clip-share.net/video/eUKlmfbJyIQ/video.html)? There's no obvious equivalent to the impact that you identify with the pop-pop boat, but side-to-side motion still seems to make the scooter move forwards rather than backwards. Would be interested in your thoughts.

  • Will Fox
    Will Fox 5 months ago

    In my teaching days we use to make these with the kids but the 'engine' was just a length of copper brake tube formed into a coil for the boiler with the ends soldered into the back of the tin boat. Without the flexible tin on top of the boiler they didn't pop so audibly but still worked. Also we didn't fill the tubes with water, just tilted the hull slightly so one exhaust was under water and the other not so a few drops of water entered one end, that was enough to set them off.

  • ArcadiaCv
    ArcadiaCv 10 months ago

    Shape of the boat might also contribute to the forward motion as well. The back of the boat is flat and has higher surface area and resistance when moving backwards, while the front is curved and pointed and lowers the resistance when moving forward.

  • PJ818
    PJ818 9 months ago

    I was thinking the forward motion may have had something to do with the front of the boat being streamlined, where the back of the boat is a blunt, flat surface that would be resistant to motion in that direction.

  • Jacob Lawrence
    Jacob Lawrence Year ago +269

    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
      233kosta Year ago +24

      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.

    • Fireball XL-5
      Fireball XL-5 Year ago +6

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

    • 233kosta
      233kosta Year ago +21

      @Fireball XL-5 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.

    • Fireball XL-5
      Fireball XL-5 Year ago +2

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

    • 233kosta
      233kosta Year ago +11

      @Fireball XL-5 You asked for empirical evidence, that is how you get empirical evidence.

  • Andrew Brown
    Andrew Brown 7 months ago

    Awesome glass job. Surface area must count for a lot in the tank as well.

  • Humbal Tariq
    Humbal Tariq 6 months ago

    The one thing you missed is the aerodynamic design of the boat when considering why the boat moves forward and not stay in its position. While you give a much more complex answer to that question, I think the answer is very simple. Considering that both push and pull forces are equal, it is alot easier for the boat to move forward due to less water resistance while moving forward, which is not the case while being pulled backwards. And to experiment whether this holds true, invert the boat design with the pipes popping in the front.

  • Sam Hill
    Sam Hill Year ago

    I think because the 'tank' in the metal boat has a lower volume than your glass boat, it's not an issue that the tank is only partially full.

  • Jacob KjΓ¦rulf
    Jacob KjΓ¦rulf Year ago +2

    After watching one of your recent videos, I was wondering on how fluid viscosity has an influence on say a greedy cup, how high or low does the viscosity of the fluid have to be before the reaction is broken

  • K B Teja
    K B Teja 6 months ago

    I guess the other reason for the boat to move forward is if you see the shape of the boat, the forward part of the boat does not have resistance due to water while moving forward because of its bow shape compared to its stern which has more resistance due to water.

  • coryman125
    coryman125 Year ago +266

    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

    • Reuben G
      Reuben G Year ago +6

      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
      Ruskiwaffle1991 Year ago +3

      @Reuben G orion right?

    • Nikarus2370
      Nikarus2370 Year ago +7

      @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.

    • John Doe
      John Doe Year ago +3

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

    • πŸŽ–οΈΧ’'Χ•Χ‘_Neuromancer2077
      πŸŽ–οΈΧ’'Χ•Χ‘_Neuromancer2077 Year ago


  • JackBond1234
    JackBond1234 Year ago

    I assumed the boat was propelled because the water inside first is expelled, and when it's sucked back in, that only stops the new forward momentum, so it's oscillating between forward motion and stopping rather than forward and backward motion that fully cancels out.

    PRASSMAN CREATIONS 2 months ago

    The pop pop works because of the 2 different metals the boiler is made of.
    I think it''s steel on the top & brass on the botom.
    The water keeps the brass cool whilst it's in the boiler thus keeping it "small".
    When the water boils out the brass heats up from the flame & expands thus pulling water back in again
    The water cools the brass, it "shrinks" agian over & over

  • Tennouseijin
    Tennouseijin Year ago

    I've seen explanations about the last topic that go like this - if you were trapped on a frozen lake that is perfectly slippery, such that there is zero friction between your shoes and the ice, if you tried to walk, you'd stay in place (or, well, fall, but stay in place). However, you could escape the situation simply by... breathing.
    Now, I'd have to see some actual calculations to estimate how quickly an average person would be able to move in such a precarious situation. I guess it would be hard to reach any appreciable speed that way, because air resistance would still slow you down, and I don't think you'd be able to accelerate very quickly. But, at least in theory you should be able to reach some non-zero average velocity.

  • Thom Vogan
    Thom Vogan 18 days ago

    I'm wondering if this effect only works at small scale or could it be somewhat larger

  • KingShin
    KingShin 10 months ago

    I think the momentum cancellation is a bit dodgy. What I think is happening, is that that the water being pushed out propels the boat forward, and the water being sucked back in brings the boat to rest. So in one cycle, the exact same amount of water is being expelled and sucked in, but the boat has moved forward by some distance. And the cycle repeats.

  • INFPail
    INFPail Year ago +48

    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
      quartercast Year ago +5

      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.

    • Ed
      Ed Year ago +2

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

  • Vikramaditya Chaudhury

    As a child, this tinplate toy was a must have every year during my annual vacation to Varanasi, India. I still have a few left, preserved somewhere within my chattel.
    Thank you for posting this video.

  • Syed Rizvi
    Syed Rizvi Year ago +1

    Until now, I used to think that due to unevenness (asymmetry) in piping geometry, the hydraulic system creates a draught. That is, water flows in through one of the pipes and steam+water mixture leaves through other. Due to the exit momentum being more than the opposing entry momentum, there is a resultant forward force. BUT, Alas, it is much more complicated than that!

  • Jason Schultz
    Jason Schultz 10 months ago +1

    I can't help but wonder how the boat would act if it weren't designed to cut through the water like a normal boat. Maybe just reverse the motor in the same boat and see what happens?

  • Nils Gensert
    Nils Gensert 3 months ago

    Could the forward motion also come from the hydrodynamic shape of the boat? Like a hooked arrow head that goes forward easier than it goes backwards, the backwards motion would simply be resisted stronger than the forward motion.