- It's absolutely frightening
if you think about it so I'm trying not to. - [Camera Man] Five, four, three, two, one. - This video is sponsored by KiwiCo more about them at the end of the video. No, it broke. - [Camera Man] Steve it was
really good, it was going. - Okay, so here's the backstory. I was putting together a stage show for kids years ago about polymers, and I wanted to show polyethylene oxide. See how you just tip
the beaker a little bit and all the polyethylene oxide comes out, it self siphons, how cool is that? For the stage show I wanted
to show a physical analogy for what's going on with that polymer. And I'd seen Steve Spangler
do it with Mardi Gras beads. Look, polymers are really
long chain molecules, and here is a really long chain of beads. So it's similar and it
behaves in a similar way. See how it self siphons from the pot, but that's noisy, isn't it? But I wanted to use metal
beads instead of plastic beads 'cause I thought they
would stand out better. I don't know why they're smaller. So they definitely didn't. But what's interesting is
they don't just self siphon. They do this extra weird thing. With the metal beads the
chain rises above the pot before it falls back down. Isn't that mental? So I did the first thing you do when you notice something strange, you go on Google and find out the answer, except I couldn't find the answer. I couldn't find any
reference to this effect. You might be thinking, hold on. It's easy to find, it's
the chain fountain. It's all over the internet,
except in 2013 it wasn't, I couldn't find anything about it. And I started to think, hold on, have I discovered something? Is this, is this a discovery? I wasn't using YouTube much back then. So I thought, you know, I'll post it. It might be a fun video. And maybe someone will be
able to explain the phenomenon in the comments. Well, that's not how YouTube
comments worked back then. Most of the comments were just about what my mum had been up to. There was also some suggestion
that video was fake. For example, that I just
reversed the footage, but come on, that's even
harder to explain, isn't it? By the way, I send one meter
of the chain from this video to everyone who supports me on
Patreon in the very top tier. But anyway, this video was
my first viral success. It was posted on the video subreddit and it got lots of views. It was discussed on the
ask science subreddit. There it is, just a brief discussion, really brief. I actually read the whole discussion. I don't think anyone came
up with the right answer. So I decided to film it in slow motion to see if I could figure
out what was going on. And I asked around, does anyone
have a slow motion camera and Earth Unplugged got in touch, another YouTube channel, they
said, "Come and film with us." You can watch that video though, I believe my explanation is wrong. So don't pay too much attention to it. There, it has got some pretty visuals. I had all this slow motion
footage and I poured over it. And eventually I worked out slow motion footage doesn't help. Actually, that's not fair. One way the slow motion video did help was that it reached a wider audience. It was picked up by the New York Times. It was on Japanese TV. It's been on QI, The
Action Lab has done it. King of Random. Like I don't wanna say
it's a global phenomenon, but this is a three-story
high sculpture in Guatemala by architect Axel Paredes
inspired by the slow motion video of my beads coming out of a pot. It's no big deal. It's just a three story
high sculpture in Guatemala. More importantly, the video
is watched by two physicists at Cambridge university,
John Biggins and Mark Warner. They decided they were
gonna figure it out. They have an explanation,
they've written a paper about it. It's called understanding
the chain fountain. They've made a video about that as well. I'll also link to that in the description. But ever since then, I thought I need to make a followup video about it. And I just dragged my feet
because I was doing other videos. I had other things I was interested in, but then I got an email from
Mehdi at ElectroBOOM saying, I think Biggins and Warner are wrong. I'm planning to make a video about it. I'll send people to your channel
at the end, is that okay? And I said, wait, I've been
planning to make this video for ages, why don't we
release them at the same time? So we've been sending
each other little videos back and forth, video messages
with the chain and everything and I thought we'd eventually
come to an agreement where we understood but even now we don't. So we're releasing both videos. We completely disagree on what's going on. And I had an idea, something I've learned
from YouTube recently, if you have a scientific disagreement, it's not official unless you have a wager. - Wager? - Yeah, a wager. So I propose that whichever
one of us turns out to be wrong gives the other 10,000. - [Mehdi] 10, 000? - Cents. - Cents, okay. - Canadian.
- Yeah. - Obviously because you're Canadian. - Yeah, sure. - What'd you think? - I think it sounds good, especially since I'm gonna win and it's gonna pay for my lunch money. No, if we can have someone
like Neil deGrasse Tyson to settle our dispute, it would be nice. So you're on. - I'll go through Biggins
and Warner's explanation in a second, but first
one of the predictions of their explanation is the further the chain has
to fall out of the pot the higher the fountain will rise. So I went on the BBC, we went up a crane about 40
meters and we dropped the chain and the fountain rose about
one and a half meters. I won't show you that footage in case it triggers an
automated copyright thing. But also I want to try it for myself. I want to beat that record 'cause at this point I actually
think it is a world record. I contacted so many people
about getting high up somewhere and UK Bungee Club were
the first one to say yes. And they were just like, yeah,
we can do that, no one else. Is it all right to spin
round to the other side here? Do you wanna get a shot
looking straight down see where we are? - [Camera Man] I can't
even move right now. - We're 45 meters up. We're outside the O2, God,
what an amazing building. Got the River Thames over there and over there 'cause it snakes around. Honestly, I've been so
stressed about getting up here. I haven't even thought
about how high up we are. - Ready to go? - Yeah. - I don't know if that's
safe but that's all right. - [Camera Man] Steve,
it directly below you. - Yeah, great. My daughter's just in the car. She's like, " I don't wanna watch it." - [Camera Man] What are we talking about? - Yeah, I've got a thumbs
up, should we do it? - [Camera Man] Five, four, three, two, one. - [Camera Man] Oh that is great. - Yeah. No, it broke. - [Camera Man] Two, one. - Here's that attempt again,
but I'm showing you the camera that's tracking the top of
the arc so we can read off how high it got. It looks to be around 140 centimeters. This is the long one, this is 200 meters. Hopefully, we'll get a bit more height 'cause it, you know, it
goes higher and higher as it is going. - [Camera Man] Five, four, three, two, wait, wait, wait, we got, and action, go ahead. - Oh my God, that's incredible. That was amazing. I'm so annoyed that it broke though. Don't you use these links to
make sure a chain is longer and I guess I just need
to get one continuous long length of chain. How'd you feel about
doing it again next month? - [Woman] You know, I'd be
happy to do it again next month. - That was amazing though. I mean, at 170 is the highest
that got on the one show. I don't think I've seen a
higher than that anywhere else. So I'm very happy with that. I didn't know those links
would break like that. The force must be incredible on it. They take a huge amount
of force without breaking. So that, I mean, it
must've been incredible. The force on that thing. I'm glad that didn't happen
when I did it on the one show that would have been
embarrassing on live TV. This is just gonna be embarrassing later on my YouTube channel. So the chain broke on both
attempts, which is so annoying because it actually means that that one meter 70 we measured doesn't equate to a chain
fountain of one meter 70 because that one meter 70
is measured from the ground, but the chain broke halfway through. So we have to measure
from halfway down the pot. Well, so look, that's
about 30 centimeters. So you need to knock 30 centimeters off. In other words, we managed
about one meter 40, whereas on the one show they
reckon they got one meter 50. I actually think on the one show, there was some parallax issues 'cause of the way they were filming it. Whereas we tracked up with
the camera to reduce parallax. It may actually be that we
recorded a world record here, but we'll never know. To be absolutely sure I
need to come back again with one long piece of
chain, no links in there. So there's no weakness in it. I think I look for a new location as well because well, the cabin was quite tight and I wasn't able to fit
the entire experiment into a wide shot. Also, I think I can probably
find somewhere higher. If you wanna be sure
to catch that attempt, subscribe to my channel and
click the notification bell. But why does the chain go
up before it goes down? Well, I gave an explanation in the Earth Unplugged slow-mo video and I think that explanation is wrong. I said that the chain leaves the pot with a lot of upward momentum and it can't change to
downward momentum instantly because an instant change of direction is equivalent to infinite acceleration and that's not allowed. It needs to take its time. So it rises up a bit and curves down. But I don't buy that
for a couple of reasons. Well, first of all, it
doesn't work experimentally. Like you don't see the
chain fountain effect with regular chain, it only
works with bead chain it seems. Second of all, we're not asking for an instant change of direction
or infinite acceleration. The change of direction can happen over the thickness of the lip of the pot. Like this, that's not an
instant change of direction and it's the behavior we
see with regular chain. So it must be something else. Well, we should be able to figure it out by looking at the forces involved, like in this simplified view, for example, we could look at the
force in this curved part, that's causing the chain
to change direction. We can do that by zooming in
on a small section of the chain and looking at the tension at either end, there's a net force towards
the center of that arc. I won't go through the derivation, but I'll put it on the screen. The end result is that
the force on the chain is equal to the tension in the chain multiplied by that little
length that we're looking at divided by the radius of that arc. But we also know the
equation for the force on something that is experiencing
centripetal acceleration it's equal to the right mass of the thing multiplied by the velocity
of the things squared divided by the radius of the arc. So these two things must be equal. Instead of writing mass as M we can write it as the mass
per unit length of the chain multiplied by that little
length that we're looking at. So now we can cancel those two Ls but here's the crucial part. We can also cancel the Rs and
that's really significant. It means that the radius of curvature doesn't play any role in these dynamics. Like the radius doesn't have to go up when the velocity goes up or the radius doesn't have to change as the tension changes. There's nothing like that. What it suggests is that for a chain moving through its own length the chain can turn through
an arbitrarily sharp corner, not infinitely sharp, but
anything less than that is okay. So long as the chain is strong enough to withstand the tension. And it really does put
another nail in the coffin of the explanation that I
gave on Earth Unplugged. The chain doesn't need time or space to minimize the tightness of the curve. It can be arbitrarily tight, it can flow straight over
the rim of the beaker and that doesn't cause any
problems mathematically. What we really need to
do is look at the tension in the chain just after it's left the pot, because we can know that
tension in two different ways. We can work it out as the tension
required to move the chain up to a certain speed and we
can work it out in terms of balancing the tension at the top and the weight of the chain in between. Again, I won't go through the derivation, but I linked to Biggins
and Warner's paper. And what find is that the
tension just above the pot is equal to this. The force required to bring
the chain up to speed. And this the tension at the top minus the weight of the chain
between the top and the pot. So these two things are equal, but we already know the tension at the top because we worked it out earlier. So let's substitute that in. Look, these two things cancel out. So that tells us that
lambda HG must be zero. In other words, the height
of the fountain must be zero. So by looking at the
forces in this naive way, we see that there can't
be a chain fountain, but we noticed one experimentally. So there must be another
force coming from somewhere, either from the ground or from the pot. Experimentally, the
chain fountain gets going before the chain has even
reached at the ground. So it must be coming from the pot but how can the pot be
producing this extra force? Well, the Biggins Warner approach is to model the chain of beads
like it's a chain of rods. We'll discuss whether that's
reasonable in a second, but first let's look at
the consequence of it. Look, here's a simplified view. You've got some chain that's still at rest and you've got some that is in motion. Look, this rod is about
to be pulled into motion by this rod. The center of mass of the rod is here and it's gonna be pulled from this end. That means that when the
rod comes into motion, it won't just move up it will also rotate. So that part of the ride ends
up lower than it was before. But actually that can't happen because the rods are resting
on the rods beneath them or resting on the bottom of the pot. So instead of this end of
the rod ending up lower than where it was, it pushes
down on what's beneath it. And every action has an
equal and opposite reaction. So what's beneath it pushes back up and then we have our additional force. Here's a great demonstration
of the effects. A block of wood is shot with
a bullet from underneath dead center on the block of wood. And obviously it shoots up into the air. But look, what happens when
you shoot the block of wood at one end instead of in the middle, it actually goes higher than when you shoot the block of wood from the middle because
of that kickoff effect. Thanks to James Pantaleone of that video, the link to his paper
on the chain fountain is in the description. Is it reasonable to model the bead chain like a chain of rods? Well, what's interesting
about the chain is it's very flexible, but if you try to bend it
beyond a certain curvature, beyond a certain tightness, you can't, it becomes stiff beyond
a certain tightness. So if we look at the
chain of beads like this, look, this corner is at maximum tightness, meaning that these few
beads here are a rigid body. Again, you can consider
the center of mass. You can consider the fact
that it's being pulled from this end. And so there will be a
downward force from this end just like there was
with the chain of rods. So it's not a perfect analogy
for what's really going on, but the mechanism is still there. Actually, this explains why you don't see the chain fountain effect so
much with the plastic beads. With plastic beads you can pinch the chain completely flat against itself. There's no maximum curvature like there is with the metal bead chain. Actually, there's another possibility for how the additional
upward force is created. Imagine two rows of beads
inter locked with each other. As the chain is being removed from the pot sometimes it's pulled
horizontally like this. If the beads are interlocked like this, there will be a kick upwards as the top row of beads is pulled along. That's two possible mechanisms
for the additional force. There may be others. These two may be insignificant
compared to those others. It would be reasonable to try
and measure this extra force. You know, the pot is pushing up and the chain is pushing down. So in your hand, the
pot should feel heavier than it would if it wasn't
for the chain fountain. It's obviously going to be very subtle and not something you can
detect with your hands. Also, if you put it on
scales and take readings, well, that's difficult as well because the mass of the
pot is constantly changing as the chain leaves. I haven't seen any successful attempt to compare the two scenarios. But what if you could remove gravity and remove the bottom of the pot, you should expect the pile
of chain to move downwards. And actually you can kind of do that by switching to a horizontal
orientation for the experiment. Look, here's a pile of chain on the table. I'm gonna pull it from this end and we'll see what happens
to the pile of chain. And they're like, you can see the recoil of the pile of chain which
is exactly what we need if there is an extra force there. You can even see the point
where the chain kicks back. It's just where the chain is
being lifted from the pile and it moves up and down the
pile as it's being pulled. At this point, you might
be thinking, well, hold on where does the extra energy come from? And that's a good question. Often with problems like this, you can look at it from
a force point of view or an energy point of view. And actually it's a
good idea to look at it from both perspectives. It's a good way to test your working out because it needs to make sense
from both points of view. Well, the whole process is driven by gravitational potential energy. The chain starts off
at the level of the pot and ends up at the level of the floor. It loses gravitational potential energy, and that's converted into kinetic energy. Again, I won't go into the
mathematical derivation because this video is already quite long and it's all in the paper which is linked in the description. But the upshot is that half the gravitational potential energy is lost as heat and the rest
is turned into kinetic energy. Interesting side note, there
are loads of dynamic problems where half the energy is lost to heat. For example, pouring
sand onto a conveyor belt or connecting a charged capacitor
to a discharged capacitor. But anyway, half the energy
is up for grabs in some sense. And the mechanisms I've
described in this video that might account for the
extra force from the pot are able to reclaim some of that energy. So it doesn't look like
we're breaking the law of conservation of energy. I recommend you watch
Biggins and Warner's video on the subject as well, the
link is in the description, but I will just play a snippet from it. This is Martin Warner
talking about the project. - We could blend this research project 'cause nobody understood the Mould effect. - I mean, Einstein doesn't
even have an effect named after him. I'm not saying I'm better
than Einstein, it's just. You know, Mould is a
difficult surname to have when you're at school. I've always worried about my kids telling people that that's their surname, but now it's like, oh,
that'd be great, won't it? They go into school
say, "My name is Mould." And people will be like, "Hold
on, as in the Mould effect?" No? And they'll be like,
"Yeah, that's my dad." That's how that will go. Right, there's something
that I really, really want to happen as a consequence of this video, will you help me? You know, we talked about
the fact that these R values cancel out at the start of the video and the consequences of that. Well, another consequence is that you can have any
arbitrary arrangements. You know, the chain can be going like this through space, right? And it will, the chain will just continue to move through that. And we've seen that actually
in the slow-mo video. The chain gets into
these different patterns. The pattern remains while
the chain moves through it. What I really want to see is on the International Space Station an experiment with chain. So I want one of the astronauts to have just the chain floating there, you know, and just to pull on one end
and to see what happens, to see if the chain will
float through that shape. If anyone knows how to get the attention of someone on the International
Space Station let me know. The main thing that me and
Mehdi disagree on is that I think there needs to be this extra force from the pot, and he doesn't. You know, disagreement is a
really good thing in science. So I really want you to
go and watch his video. See what you think about it. Obviously, leave comments, be civil, come back here and leave
comments here as well. And he has loads of great videos. We've collaborated in the past. If you're not subscribed
to his channel already, you really should be. Do you think this is more fun than watching daddy
throw beads off a crane? - Beads off a crane? Nothing, I've been getting
Kiwi crates for my kids for almost a year now. So I'm really glad that they're
sponsoring one of my videos. KiwiCo put together these projects. They come in the post once a month. Everything you need for the
project is there in the box. There are eight different
subscription lines for every possible age group. For me, I get these crates because I love to see
them getting excited about making and building, like
those are my fondest memories from childhood. And, you know, I think we
need more makers in the world. But two things that
really stick out for me the first is it's not just the build, there's always a STEAM angle to it. Science, technology,
engineering, arts and math. So for example, you're
building a kaleidoscope, but you're also learning about symmetry or you're building a robot but you're also learning about coding. The second thing is the replay value. You're not just building
something and then that's it. Like for example, with this one, there's a puzzle element at the end, you work through these puzzle cards to try and get the little robot
from one end to the other. And every crate comes with a magazine full of additional ideas to
explore and things to do. You know, I love the long
summer holidays for my kids, but it's kind of crazy
that we take them out of formal education for
such a huge stretch of time. Like we really needed
to their brains working in that period. And I can really
recommend KiwiCo for that. Like start your subscription
at the start of summer. See how you feel when you
get to the end of summer. You'll probably wanna keep going, but for that stretch of time, it's gonna be a great
way to keep them away from TV and screens. And you can get the first month for free if you go to my special URL, kiwico.com/stevemould, the link is also in the description. So check out KiwiCo today. I hope you enjoyed this video. If you did, don't forget to hit subscribe and Todd thinks you'll
enjoy this video next. Who is Todd? (upbeat music)
I think Mehdi is half right, but his video is kind of self-disproving.
He does do a good job of showing that a chain loop will hold its shape just due to momentum (and I think he's 100% right about that) but in the floor test and the whiteboard test, the loop never rises like it does with the metal beads.
That suggests that there is still a missing force pushing the loop up, which is nicely explained by the pushback force.
In Steve's video, the demonstration of the beads being kicked backward shows that it is contributing at least some force. This force is small, but the loop moves up slowly, so that's what we would expect.
EDIT: Also, I don't know if I buy Mehdi's explanation of the friction on the rim as stopping the loose chain from rising. As a chain bumps along the edge, it will get kicked up into the air. It will then either rise if there is another force (like the segmented chain), or slowly drop back down (from friction or other losses) if there isn't, and hit the edge repeatedly (like the loose chain).
You talked about doing the experiment in weightlessness, and mentioned doing it on the ISS, but there's actually a way to achieve weightlessness down here on the earth as well. I was reminded of a video by Veritasium where he achieves it by using an airplane. Here's the organization's website. They conduct flights for the general public, but they also seem very keen on scientific research, (and it'd also make for a very interesting video,) so it looks like they're very fit for the job
Steve, I think you (or Mehdi) should try the horizontal experiment starting with the "reserve" of chain straight and without loops. That way there can be no "pushing off effect" and you can check if it's just momentum.
The problem I see with the horizontal test is that in the regular effect, the chain is accelerating constantly due to gravity, while in the horizontal test, the human will probably reach a speed plateau.
I think Medhi is on the right track because he looks at it dynamically, where as Steve has more a static approach. I think acceleration is key here. Based on the observation of need to kickstart the effect with shorter chains, I think acceleration produces the fountain and constant speed can sustain it.
Medhis horizontal floor experiment could be repeated with a chain driven by a sprocket. This way you can control the accelleration and see the effect it has on the "height" of the Mould effect.
Main explanation
I guess I'm going to throw my two cents in. Sorry if someone else has already suggested this. I haven't read all the comments but I'm like 99% sure I know what's going on.
Imagine a short rope being pulled down over a pulley by a heavy weight. When the pulley runs out of rope we expect it to whip up at the end. This is because the force accelerating the end of the rope quickly changes from being pulled up by the pulley to being pulled down by the falling weight. The acceleration changes almost instantly, but the new acceleration is only the provided by the free-falling weight, so its not infinite. The end of the rope continues moving upwards for sometime until the acceleration catches up with it and it starts falling. The key is that the end of the rope continues moving upward for some time before falling down.
Now replace the pulley with the lip of a container. In this case, everything still behaves the same, just with some added friction that results from removing the proverbial perfectly massless, perfectly frictionless pulley.
Now replace the rope with a heavy chain. Each link in the chain has some significant amount of mass that cant be accelerated quickly. Working backwards from the end of the experiment, the last bit of the chain will be whipped upwards as always. Just before we reach the end of the chain, those next-to-last links are STILL being whipped up by the tension from the links before it, they are just ALSO being weighed down on the opposite end by the weight of the links they are pulling on. As they continue to rise, they effectively have to pull more and more mass as they pull upwards on more links below them. Eventually, the downwards acceleration catches up with it and the link starts moving downwards, but it never whips up like the end of the rope because of this extra baggage. If the upwards force on the chain link is enough that it doesn't start heading downwards until after it goes past the lip of the container, you get the chain fountain effect.
Why this effect doesn't happen all the time
There are a couple of things that make this hard to achieve with most setups. You won't see any effect at all until the upwards acceleration on each link is enough to keep it moving beyond the lip of the container. In order for it to be interesting and viral-worthy it also needs each link to go significantly higher above the lip of the container than the rattling of the chain would provide alone.
The higher the chain fountain effect goes, the more force is working against it. The links at the top of the arc are being pulled down by the weight of the rising chain below, its own mass, and the force provided by the falling chain on the other side. The extra mass to lift lowers the maximum height of the arc.
Each link in the chain must be massive enough that it takes some time for the acceleration to reverse its velocity. Otherwise it can just change direction over the lip nearly instantly.
At the beginning of the drop, the lip of the container is close to the topmost resting link. However, there aren't a lot of chain links pulling down on the other side either, so there isn't much upwards force. At the end of the drop the resting links have much farther upwards to go to reach the lip of the container, which counteracts the upwards force provided by the weight of all the falling links.
Friction adds an additional downwards force on each link. As Mehdi pointed out, most "normal" chain links will bang on the glass repeatedly due to their shape, especially because normal chain links cant lie flat on top of each other. This wastes a significant amount of that force on each impact.
Additional evidence that didn't fit in the main explanation:
The higher the chain was dropped from, the higher the arc was able to get. This is because the upwards force pulling links out of the container keeps increasing until the bottom of the chain hits the ground (or until it is equalized by friction). If the force were being provided by the container, the height of the drop wouldn't matter.
The distortions in the chain fountain are preserved as the chain moves because the force moving the links is the tension from the link before it. As the imperfect, tangled links in the imperfect container move upwards they cause the perturbations that make the pretty patterns. Each link is pulled directly towards the one before it so the shape is maintained until more perturbations are added.
The plastic balls didn't work well because they weren't heavy enough. Switching to the metal ones added the required mass to make the effect interesting.
I'll see if I think of other things to add. Sorry I don't have any calculations. I'm very much an armchair physicist. Thanks to both Mehdi and Steve for the interesting experiments.
EDIT: formatting. Also Thank you for coming to my TED talk.
Medhi is… 100% wrong. He fundamentally misunderstands the effect. In short all of his tests show the apex of the loop traveling in the direction of the primary momentum. But in the mould effect the apex of the loop is traveling in the opposite direction as the primary (or net) momentum. (Feel free to call this the Moses formulation of the Mould Effect)
Let’s examine a few of the Medhi tests. In each of his “successful” tests the apex of the loop is traveling towards the direction of the primary momentum. A loop is created first (either by picking up the chain and throwing it down or by laying out a loop on the 2d plane) and then the loop persists. But the loop never gets higher than the point he starts with. If he had placed a “lip” at that point where the loop starts in each test the chain would be banging on the top of the lip for the entire duration.
Issues of “lack of acceleration” do not solve this. The 2d test should show the effect from any amount of force applied. At the very least this because it’s impossible to not accelerate. So while Medhi may have had constant velocity through a good portion of his tests he could not have had constant velocity through all of them. If acceleration were the issue then those 2d tests would have show at least some positive movement of the loop. But they do not.
The vacuum example is the only one where the loop does move up… but the “chain” is moving the wrong direction. The loop is created and moves in the same direction as the primary momentum. (Which is the long portion of the vacuum hose moving fast). This is the opposite of the mould effect.
The math bears this out that it cannot be momentum based either. A chain only transfers momentum under tension so the mid point on the loop cannot have a velocity away from the net force applied to the chain. The next chain will but without an additional force applied to it besides the net tension the force in the direction away from the net force on the chain should be at most equal to the force pulling the apex in the direction of the net. Hence it cannot have a higher relative position on momentum alone once it becomes the apex position
So there must be some other effect giving the chain a positive force. It may not be the lever force but without a better explanation it sure looks like that lever force.
I think you're both right. I think you're talking past each other. It's just a standing wave. It's like when your hose is on the ground and you need to get it over a rock so you flip it and a wave travels down the length of the hose. Mehdi is driving that point home. But Mould is interested in why the ball chain wave rises, and I think it rises because of the factors he's mentioned, but those factors aren't what sustain the wave, they are the factors that grow the wave. Mehdi is talking about what sustains the wave and Mould is talking about what grows the wave.
Going to be honest, I agree with Mehdi's conclusions on this one
my money is on electroboom