- This video is sponsored by Babbel, the best selling language learning app. Me and Mehdi released two
videos at the same time giving different explanations
for the chain fountain. The person with the correct explanation gets 10,000 Canadian cents
from the other person. And judging by the comment section Mehdi made the more convincing video. Dammit. Some commenters said that
not only was his explanation correct, but his approach was better. He came up with hypothesis
and tested those hypothesis. Whereas I was just
interested in trying to break a world record and frankly
that is a fair criticism. So I am back with some
hypotheses and some tests for those hypotheses and some simulations. I did offer to concede the
wager based on the fact that more people were
convinced by Mehdi's video, but he very graciously
refused saying that the wager should be decided based on science. The crux of our disagreement
is the fact that I think for the chain to rise up in a fountain there must be an extra kick-back force from the pot on the chain
as it's lifted from the pot. But Mehdi doesn't think that
extra force is required. For more details about that disagreement, you can watch the original videos. The links are in the
description and in the card. To prove his point Mehdi put
together this ingenious test. The beads on this chain
are really spaced out, which removes any kickback force. And yeah, look, here's the Mould effect. But actually what you see
here is quite different to what you see with
the normal bead chain. With normal chain it
starts off as a dribble and grows into a chain
fountain on its own. Whereas in Mehdi's test,
he imparts the shape of a chain fountain to the
chain at the beginning by hand. And that fountain then
slowly decreases in height under the influence of gravity. So my argument is that
this isn't a demonstration of the chain fountain. What it does demonstrate
is that a chain will flow through the shape that you
give it, and that shape would be maintained in the absence of gravity. In the presence of gravity,
the shape that you give the chain collapses over time. The fact that a chain flows
through its own length in this way is an important
part of the explanation. But we also need to
explain how the regular type of bead chain is able
to rise up against gravity and stay there. I think it's good, actually,
to split the explanation into two parts like this. We need to explain first how a chain, moving through its own length,
will maintain its shape in the absence of an external force, like gravity or friction. And we need to explain how the fountain is able to rise up on its own. Let's tackle the first
part of the explanation. Look, here's another demonstration
on a horizontal surface. So there's no issue with gravity here. As I pull the chain around,
it moves through the shape that I give it. Actually the shape does
collapse a little bit, presumably because of
friction in this case, as opposed to gravity. For an intuitive
explanation of this behavior you can think about it in terms of waves. Like if I whip this chain, the
wave travels down the chain. But if the chain were to be
traveling in this direction at exactly the same speed
as the wave was traveling in this direction, then the
wave would appear to be fixed in space with the chain moving through it. Interestingly, when you
look at the mathematics of a chain falling off a
table the wave speed matches the chain speed. So when Mehdi whips the
chain in this experiment, the wave he creates
travels in this direction and the chain travels in this direction. The end result is that that
wave is fixed in space. So that's the first
part of the explanation. But what about the second part? How does the fountain rise up on its own? Well that was the subject
of my previous video. I think that the chain
rises up against gravity and can hold there because of
an additional kickback force from the pot. But let's just look back
at Mehdi's spaced out bead chain experiment. He actually has his own explanation for why the chain fountain
decreases over time in his test. He puts text on screen to say
that it's because the chain is slowing down and he needs a higher drop for a higher speed. So I set up the same experiment
with spaced out beads and an eight meter drop. And I've marked every 10th
bead with black marker so we can see from the video
how fast the chain is going at different parts during the test. It's my hypothesis that even
if the chain increases in speed over the course of the test, the fountain that I impart manually
by hand at the beginning will still decrease over
the course of the test due to gravity. According to Mehdi's theory,
under those circumstances the chain fountain
wouldn't drop over time. Well clearly the fountain
does decrease in height over the course of this test. But how is the speed changing? Well if we count from this
frame towards the start of the test, it takes about 40 frames to get through 50 beads. And if you count from
this frame towards the end of the test, it takes about 30 frames to get through 50 beads. So throughout the duration of the test, the speed of the chain is increasing. And yet the fountain
that I imparted manually at the beginning still
decreases in height. In general though, if you could
demonstrate a very flexible chain rising above the pile on its own that would be strong evidence
against my explanation. And it's important in science to try and prove yourself wrong. Which is why I tried to
recreate Mehdi's test in the first place using
longer chain and a higher drop. But so far I haven't seen a fountain. But if you wanna try the test for yourself with an even longer chain, from an even higher drop, then
please do send me the video. Maybe post it on my subreddit. By the way, with the explanation
broken down into two parts like this, it's worth
looking at the history of our understanding of it. Because the first part of the
explanation has been known for a while. This textbook from 1860 talks
about chains maintaining their shape when flowing in steady state. It's only the second part that's new, the fact that a chain
can rise up on its own. That's why, for me, that
is the Mould effect. That's the chain fountain I wanted to take a closer look
at one particular experiment of Mehdi's that seemed to be
really persuasive for people. It's this horizontal setup
where the chains in the pile are spaced out like this. Actually, I'm just gonna
rotate this video to vertical. That way we can talk about
up and down on the screen and it's equivalent to up
and down when we're doing the experiment for real. That way everything's nice and analogous. With the chain spaced out
like this there can't be any reaction force from the
pile as the chain is picked up. It doesn't have anything to push against. So I would argue that what
we're seeing here is a chain maintaining its shape. It's the first part of the explanation. The fountain doesn't actually grow. It does appear to grow in height, but that's just because the
top of the pile is receding in this direction. If you look at the peak of the fountain it doesn't get any higher, it
actually moves down slightly. Probably due to friction. So I wanted to set up
this test for myself. In one version the pile
of chain is spaced out and in the other version the
pile of chain is bunched up. I also wanted to control
the speed a bit better so it was the same in both tests. So instead of just grabbing
the chain and running with it, I've created this motorized spool. I say motorized spool, it's
a tube attached to a drill. It's my hypothesis that
in the bunched up case, the peak of the fountain
will actually rise up and in the spaced out case it will actually recede downwards. And look, that's exactly what we see. Here are those two tests again
but this time with an object representing the lip of a beaker. To me this suggests that
for the chain to rise higher than its starting point there
needs to be a kickback force from the pile. And as before you can see the recoil of the stationary chain quite clearly. Something that's been
really helpful in the making of this video is the
Steve Mould subreddit. I'll leave a link to
that in the description. It's a great place to
discuss the sorts of things that I talk about in my videos. But when I posted the chain
fountain video it sparked loads of debate, people posting new ideas and stuff like that. Including some simulations
of the Mould effect. This simulation by Maarten Baert
is a rigid body simulation, and it really shows the
importance of the flexibility of the chain. On the left the maximum bend
between two adjacent beads is 20 degrees and on the
right the maximum bend is 90 degrees. You can see that born out in the loops of chain at either side of the pot. On the left those loops are large, on the right the loops are small. The less flexible chain on the left exhibits the chain fountain effect. The more flexible chain
on the right does not. I asked Maarten if it was
possible to extract information about the forces involved,
'cause I wanted to see if there really was this
kickback force from the pot. And he produced this animation
here where you can see the force on the bottom of
the container from each bead. And look, as each bead is
picked up there's a spike in the force. And of course every action has an equal and opposite reaction. So the bead feels a force from the pot. I also wanted to see if
it was possible to kill that kickback force in the simulation to see if it kills the fountain. One way to do that is to just
remove the bottom of the pot. Of course, if you remove the bottom of the pot then the beads
will just fall through. You have to remove gravity as well. So in this simulation
halfway through the bottom of the pot is removed and the area in red has gravity turned off. Look, you can see the
chain moving downwards. There's nothing there
for it to kick against, there's no reaction force, and so the fountain slowly recedes. Here's the simulation
again but with the floor of the pot removed from the beginning. And the fountain never happens. This simulation by Richters Finger, instead of being a rigid body simulation considers the chain to be springy. Like it resists being bent like this. And we see that when the
chain has some stiffness in this way, when it resists being bent, then we see a chain fountain. But if there is no stiffness,
if it's completely flexible, then there is no chain fountain. Richters also plotted the force
felt by the base of the pot. Look, this baseline force
here is just the weight of the chain pushing down on the pot. And obviously that weight slowly goes down as the chain leaves the pot, which is why there's a
slight gradient here. But in addition to that
there are these spikes, or at least there are spikes
in the left-hand chain where there is stiffness. Each of those spikes represents
the extra force on the pot each time a bead is
pulled up from the pile. In the fully flexible
chain there is no force and therefore there is no fountain. From these simulations it
does seem as though a force from the pot is required
to raise the fountain. It is worth saying though
that simulations are tools and they're only useful
tools in so far as they do a good job of representing the real world. So it's good to exercise caution. And actually I'll link to the source code for these two simulations
in the description if you want to take a look. In the paper by Biggins
and Warner they suggest that the stiffness of the chain
leads to a levering effect. So it seems sensible to
model the chain as a series of rods joined by flexible links. In other words, loads of little levers. It's interesting though
that if you actually build that the fountain doesn't
work particularly well. Atomic Shrimp made an interesting video where he explores, among
other things, the smooth way that the chain moves. The inflexibility of the chain
leads to this smooth motion that perhaps reduces things
like knotting and tangling. Whereas in an actual chain
of rods, the tangling is very present. I managed to find this chain
whose movement is even more limited than the bead chain. You can hardly bend it at all, really. And look, the chain fountain
is quite pronounced, even in this short length of chain. If the important thing is
stiffness then we should expect to see the Mould effect in
any chain or rope or string that has stiffness. And actually we do see it
under certain circumstances. Check out this video from YouTube channel, "HowNOTtoHIGHLINE." See how this rope develops a fountain. At this point you might be thinking, "Well if the stiffness of
the chain is so important, how does it work with regular bead chain? 'Cause regular bead
chain's really flexible." Look how much I can pinch it. Like I can't pinch it completely flat, but like that's a really tight curve. But actually what's
interesting with bead chain is when it's under tension
and you try and curve it the maximum curvature is much lower. Or in other words, the smallest
loop size is much higher. So that probably plays an important role. Thinking about alternative
mechanisms that might produce an upward force from the pot. Reddit user tnb1k produced this video that shows that when you have
a loop of chain on the ground and you pull from one
side as the loop untangles you get a kick up. To amplify that effect
they created this series of figure eight loops. And look how high the fountain goes. Isn't that impressive? You know, seeing as this
thing is already made, I might as well try it out
on the actual, you know, beads in a pot. See how high we can get the fountain. The title of this video
is somewhat adversarial, but actually having this disagreement has been really enjoyable. And that's thanks to Mehdi. If you haven't checked out
his channel, ElectroBOOM, already you really should. Also check out Atomic Shrimp's channel and the HowNOTtoHIGHLINE channel. All those links are in the description. My kids speak much better
Spanish than I do, by a long way. Because their mum speaks Spanish and because they went to a nursery where everyone speaks Spanish. And it's kind of embarrassing. So I've decided I'm
going to learn Spanish. I'm gonna do it using the
sponsor of this video, Babbel. Babbel is a language learning app. It's not just because it's embarrassing, it's because I want to be able to support and encourage their continued
learning of Spanish. I don't want them to lose
that language that they have. Also, I want to be part
of the conversations that they have with my wife. You know, my excuse was
always like, "I'm dyslexic. I find it hard to learn things by rote so I can't learn a new language
'cause of the vocabulary." But do you know what? Okay, like if you want to
learn something by rote, like vocabulary, then the
absolute best way to do it is with something called
spaced repetition. (speaking in a foreign language) (Steve speaking in a foreign language) Spaced repetition is the
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can get up to 65% off with my special URL. The link is in the description. So check out Babbel today. I hope you enjoyed this video. If you did, don't forget to hit subscribe and the algorithm thinks
you'll enjoy this video next. (upbeat music)
I like the way you and Medhi are bringing the scientific discourse to the public in this way. This is what good science communication should look like!
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great video! Mehdi convinced me with the last videos, this one has convinced me the other way. How cool to see the Mould effect in simulation form!
I think I was leaning more towards Steve's explanation last video itself, because it seemed like the bigger argument was regarding the difference in definition/understanding of the Mould Effect.
I think Mehedi (and me too initially) understood that it was the shape the "chain" made as it fell - the raised arc. However Steve's video made me understand that the Mould Effect is when the chain Continues to Rise (there is an increase in the height of the arc) as the chain continues to fall.
So Steve's explanation that in Mehedi's case, the chain never "rose" beyond a particular point of "height" was the point that cleared up the definition for me.
Have not yet watched the end of the Video so forgive me if this is already discussed.
My thoughts as to why the kickback occurs in the bead chain is due to how the chain resist being bent. I think as long as the chain resists bending beyond the angle of the arc upwards there will be almost a spring board effect from the bead which has just lifted from the base of the beaker(or beads piled on top of the surface of the base of the beaker) against the next bead in the chain which is still in contact with the base.
In short we could consider any line like this as a section of nodes and linking lines. If we assume that each link only has a certain degree of movement when attached the centre of the node when we can view the bead chain as only two nodes and one link and extend indefinitely. The limit to degree of movement(angle it can stray from perpendicular from the node) is what can cause the spring board effect.
This would also explain why the beads dont rise in Medhi's spaced out chain as the link between each node is not rigid and therefore offers no levage. This would also explain why when dropped from the horizontal arangement the mould effect still occurs as because as soon as one of the nodes needs to rise up even a little higher than the available degree of movement in any given link-node that helps boost the next node higher and therefore increasing the spring board effect.
So far this would in theory cause the moudl effect to increase in height indefinitely which is why i offer the following explanation.
I believe that once the bead chain has obtained enough speed and hight it reaches a stabalisation wherein the speed itself keeps it in that arc with diminished input from the spring board effect when leaving the base as the length of beads now moving upwards in the arc would offer slight dampening as the link can recess slightly inside each bead.
Open for any thoughts or questions as I could be completly wrong.
I'm 100% convinced you're correct. When I watched Mehdi's video I noticed that with the chain pulled on the floor at no point did the "fountain" rise - it was constantly moving towards the direction of the pull. You only have to see that Olympic twirly ribbon event to see how a pulled chain should expect to behave under those conditions. The only times the fountain has risen *against* the direction of pull is when it's been able to kick back against something - itself or the pot. Which is what you'd expect, something pushed *this* way can only be because of a reaction *that* way.
This is science. Exciting to follow. Great work! Mehdi’s a super smart guy too and it looks like you won this round, but I hope you guys do more challenges! Seriously thank you for caring about effects that might seem silly or pointless to most ppl.
Btw I’d sign up for Babbel but they don’t support the language I want to get better at - Punjabi.
I'm a little anxious about how different chains are getting run under different controls... So some comparisons don't seem to truly isolate a principle. The comparisons are sometimes changing two or three things at once.
The one I most want to see...the super floppy homemade chain with the painted black beads. That gets pulled off of a horizontal surface instead of out-of-a-beaker and hitting a lip.
I'm not convinced the early effect of the lip is not important. It forces the first leader of chain to go up no matter what.
Hmmm as to the 2d experiment comparison, I think it's not correct to say that they are comparable - in one the chain is bunched up near the top of the imaginary container, in the other the chain is spread out much lower. So in effect you have much more potential energy in the first system. Intuition is telling me that the second chain would have to travel quite a bit faster in order to maintain the same fountain height since it has to travel a longer distance - no matter what causes the effect. So I think the experiment neither proves nor disproves the origin of the fountain as the "kick" that causes the chain to rise might simply be overwhelmed by the extra distance the chain has to travel which causes it to lower instead of growing. Does it make sense?
Btw can someone explain to me in a more intuitive way where the "kick" comes from in Steve's theory? I am left deeply unsatisfied by the action-reaction explanation. In my current understanding it seems analogous to saying that it's the ground that pushes a basketball player when they jump to score a point. Sure, from physics standpoint you can say the ground pushes with equal and opposite force the foot of the player but that doesn't mean the energy is provided by the ground. And to me that seems to be a crucial difference.