The Royal Society - 2014-01-15
Over 2.5 million viewers, including many physicists, have been astonished by Steve Mould's videos of a chain flowing along its own length from a pot to the floor below. Apparently defying gravity, the chain rises above the pot as a fountain before falling down. Proceedings A has published a paper which explains why this fountain occurs by considering the forces bringing successive links into motion. In this podcast, authors Mark Warner and John Biggins explain what is going on. For more information see: http://rspa.royalsocietypublishing.org/content/470/2163/20130689 For a collection of related problems to work through go to http://www.rutherford-physics.org.uk/
4:15 Boom! Headshot!
I think something that is not being explained here is that the chain of beads that the original experiment is done with is similar to the rod analogy because a set of 3 or so beads acts as a single rod. A sort of bendy rod that propagates through the chain where the beads are pushing against the bucket.
+Christopher Soto This appears to have some validity as well.
@Christopher Soto exactly!
The gentleman doing the experiment in the stairwell with the round beads connected with a longer filament specifically says these spheres when rotated don't generate that upward thrust which got me wondering why the spheres in the original experiment did. Thank you for pointing this out!
Following up on that, could part of the upward thrust of the "rear" ball in your example (the upward ball is thrust by the one or two behind it) also be partially attributed to the design of the linking material? The chain in the original experiment, I believe, is actually a series of small spheres on a thread separated by quite short and narrow cylinders of the same material. Thereby the flexibility of the chain is lessened resulting in an increase in upward force. For example if the macaroni experiment had round pasta pieces roughly to scale with the original experiment's chain between each macaroni piece it might have produced the same results. Likewise, in the experiment with heavy beads separated by flexible filament, it might have created better results if there were a tight row of macaroni between each bead.
Right. they must try a slow motion version so that they would see how many times the beads bumps to the edge of a bucket and generate the lift up effect cause by the speed as it pulls by gravity.
the lead spheres appear to follow a curved path at the end of the demonstration.(slow down the playback)
i doubt the explanation proposed.
It looked like right before it started to curve outwards the beads kinda bundled up together. Most likely when the beads bundled together instead of directly curving over they were able to build up horizontal pressure, shooting them outwards before they then went back into usual formation.
There is a surprisingly obvious analogy which will make a lot of your viewers familiar with this concept... the kick imparted on the chain link is analogous to a skateboard ollie.
How is nobody noticing this?!
4:15 Boing! :D
@TheslowMoguys should do this so the 'mystery' would be solved! (^.^)
7:01- similar physics to that of the ollie in skateboarding
Now do it with a rope instead of spheres linked by rods.
When you explain how the chain 'pops' up from a push from the pot\table, causing the chain-rod to rotate, it reminds me of doing a skateboard ollie.
Just working out the forces and energy in an idealized scenario, I calculated that in order for the arc to not fall, the speed at which an object would hit the ground if it were falling from the initial height of the chain must be greater than or equal to the speed at which an object would hit the ground if it were falling for as long as a single link is in the air. In other words, the links must reach the ground before they would if they were to simply be dropped as individual pieces with no initial velocity.
It would be interesting, and possibly insightful, to view high-speed footage of this.
We've got it! Understanding the chain fountain.
@The Royal Society but you don't understand it, here are the facts: http://edwardwechner-13.blogspot.com
+The Royal Society
Eh, I thought your explanation was completely wrong but now I think it might just be poorly communicated. I really can't tell why the people in the video think the fountain occurs. Maybe if they described it in terms of energy instead of force, then I'd get it. Obviously the container doesn't add energy to the system, but it (and the chain) can store some like a spring does, and then re-release that energy.
+Edward Wechner
Your explanation seems refuted by the experiment where no fountain occurred.
+The Royal Society What a 'chain' of events!
+Edward Wechner They clearly explain in their paper why a chain fountain is observed in the original case.They also modeled a link of a ball chain as consisting of three identical points masses. If the links between the metal spheres approach zero then the fountain height does not depend on the absolute size of the link, so their model would still apply in the continuum or string limit b → 0'.
brilliant!
Great video, and very cool experiments. I wonder how that interesting standing wave on the left side of the parabola comes into play as well.
4:14 it was close
Great explanations!
Pretty damn interesting thanks
The type of chain in the original video is called BALL CHAIN which consists of spheres interconnected with rods. It is not a chain of beads, it is a chain of alternating beads and rods.
정말 유익한 강의입니다!!
MOULD EFFECT!
Super-interesting! Thank you for sharing!
But what actually happens... in physical terms, is way more complex then described in the ''explanation video''!
When beads are connected using the rigid fixed distances, the chain becomes another physical entity - the wave!
Therefore - chain should not be approximated with ''falling ball'', as it's not a single object anymore. It's more than only a sum of connected objects. Chain is actually a ''collective object'' and - when it's set in the motion - it's been upgraded into the wave : )
Once the physical chain becomes a wave - full-scale explanation of it's behaviour - can't be covered by ''wiring'' only simplified mechanical theories of Newtonian physics...
When set in motion - we should assume that the chain has dual nature: It's both physical object made of many (but same) individual objects, and... it's also a wave : ) And the fun just starts here...
If your explanation is accurate, then you should expect that the links on their way up and out would be crammed together. You could use a high resolution, high-speed camera to record the chain fountain to prove this behavior.
An enlightening tour round this curious effect. Even I could understand it...sort of!
What if the macaroni beads were separated by longer and flexible lines between them? You second sample is made of spherical beads, and so are the self-siphoning beads in the original Mould video.
pure awesomeness
I've heard similar explanations for perpetual motion! Pot power LOL.
A Skateboard can explain this effect well...
Interesting stuff
great video!
Gravity visualized.
Could you put it on a scale and measure that force?
Very clear and understandable explanation.
Ciekawe, ciekawe :)
Pozdrowienia dla SciFuna ;)
I found something similar to this while watching a video on cannons. They have these types of cannons where the projectile is attached to a long bundle of string, when the cannon shoots it pulls the string with it. The string in the video I'm talking about is wrapped up in a circle and as the projectile fires, almost the exact same thing happens here. It pulls it out of the bundle, and as it goes over the edge, even tho the projectile is hundreds of feet in the air the string jumps up over the edge as shown here. The guys who ended up explaining why this happens to the beads in this video talk about how 3 of the beads together form basically a block that can't bend or something like that. Anyways, I'm trying to figure out why this would happens with a string that has no beads, think of it as like a burlap type string. Here's the video I'm talking about, the same thing happens at 10:24-10:29 . While watching it, it doesn't have as a great effect as the beads in this video and I think that's because of the fibers on the string being caught and pulling it down but you can definitely see the same effect happening if you repeat the clip a few times.
https://www.youtube.com/watch?v=KDpCJfvP0O8
"Driven around"? What does that mean?
does this work with ropes?
I think it should. Why don't you give it a try
It would have been hilarious if he didn't catch the ball 3:19
Have you considered that the change in direction of a mass would produce a resultant outward force? The momentum of each bead makes it travel in a straight line unless a force is applied.
As each bead is forced into a curve at the top by the weight of the downward side there will be a resultant outward force which has a vertical component supporting the loop. Basically the same effect that produces centrifugal force on the rim of a wheel.
The height will be dependant on the speed which in turn is dependant on the vertical drop.
EDIT below. Looking at the original video, I find it interesting that near the end of the run, the height of the fountain decreases. That shoudn't occur with the given geometry. Could this observation help in a better explanation?
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In addition, this configuration of chain is easily something that can support (be a mediun) a transverse wave, so I believe the wave angle needs further examination. There &will* also be a charactic impedance of the chain for this transverse wave. Unfortunately, the vertical falling section of chain does not appear to have any wave along it., so propagation from that end is unlikely if not entirely impossible. The curved section, however, has the ability to be the source of a wave.
Interesting...
I've never heard of the coal belt paradox...
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My original thoughts centered around the simple thought that the velocity of the falling chain is such that it imparts that same velocity on the shorter rising section. Since the shorter section is shorter and more importantly lighter, it will acelerate to a higher speed than the long section is falling at ...until gravity slows it and that point is above the jar rim. This certainly makes sense viewing only the vertical velocity component of the chain, no?
This also seems to be supported by the higher fountain for the longer drop.
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EDIT: However, the up and down speeds are the same or the chain would either continuously climb higher as a function of time, so that's a bad hypothesis. In additionm since in what one might call the 'steady state' the chain is at a constant height, until the very last bit (in the original video)...strange. This is one of those thing like airfoil lift. quite complex and requiring several inter related phenomena.
This one will keepo folks awake at night...
... EDIT: I also do not appreciate the conparison to the ball trajectory @ 3:17-3:44. The vertical compoment of the chain velocity does indeed stop at the top. However, I agree that is is a poor analogy in the first place.-- Cheers
Actually the point where the chains push down decrease in height, so that the floating bit sinks down
@Liu Samuel I don't follow that logic. The length of falling chain, for all practical purposes, is constant. There is no reduction in the dowanward falling length. Once the first link hits the ground, the geometry is constant until the last link is lifted...
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Correct me if I am wrong, BUT ...The chain resting in the jar and the chain already on the ground can have no effect on the dynamics, .
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I'm ready for this going the route of the 'Bernoulli Principle' and Wing lift...
What you are saying certainly makes sense, but I think the place where a resultant force is applied at(which is the pile of chain resting beneath) is constantly changing in height. In the mechanics bit I think they just model it as a fixed point. Rather than something to do with dynamics or mechanics, I guess the problem might have been where the chain fountain dilemma came from: in adequate detail of modelling. Well I don't know I may be BSing, forgive me haha😄
@Liu Samuel I now have seen other examples where the height does not appreciably change at the end. I always considred the height to be from the current surface of the pile of chain in the beaker.
i could see some really good discussions on this ....reminds me of siphoning diesel ....just lacking the liquid and....hoses ....right?
In an idealized model, the upward and downward velocity of the growing fountain is 1/13*(2sqrt(10)-1)g*t and 1/13(7-sqrt(10))*g*t, respectively. A very nice problem.
i think they need to watch a slomo vid..
Interesting video.
Entertaining. Now I know physics is fun!
Getting SmarterEveryDay
how crazy is it that iv just come form watching a smarter every day video about fluid mechanics with the guy in the start of this video(steve), I then watched a video on his channel about the chain and now I'm watching this video where you commented, 5 years ago about smartereveryday, the channel I originally came from.
I wasn't aware that common core was International
Maybe I'll try the macaroni chain with Iris(6) and Juno(3)!
Slinkys do this too
So if one would put the pot on a weight while a bead fountain is running, will the pot be heavier than expected because the beads push the pot down while they are going up into the air?
I don't think so, as the pot would empty out at the same time...
You should also check my other comment.
Very good question. Idt his hypothesis is correct though.
He's assuming that the fulcrum would be the center of the rectangle, however, in reality it would be the bottom left corner. In his ruler example he forced the fulcrum to be the center of the ruler.
Maurício Girardi Schappo - 2014-05-18
It is a very clear and nice explanation. And it's been cleared demonstrated by experiments. Nevertheless, I don't think that it is the table which kicks the original chain, because the original chain is made of spherical beads (and not of cylindrical rods). As John Biggins noticed in his very clear and nice explanation, the spherical bead rotates around it's own symmetry axis, and doesn't try to push the table down while being pulled up by its immediate lifted neighbor.
Instead, the beads of the original chain are closely connected to each other, such that when one tries to curve the original chain, it will not curve in angles greater than a specific degree. It is easy to notice that: you just need to put the tip of the original chain at rest on the edge of the pot: the chain will curve, but it won't curve 90 degrees, as the greatly spaced chain of beads would do. Rather, the original chain would form a circular curve around the edge of the pot.
Thus, the extra kick in the original chain (made of spherical beads) might come from the next bead in the chain (the second one in the queue to be pulled off), and does not come from the table or from the pot, as very well explained for the rod assembled chain of macaroni. Again, just because you have a bend limit for the chain of tightly close spherical beads.