ElectroBOOM vs Mould: Who's right? How does a chain fountain REALLY work? Mould effect explanation

In this video I try to share my hypothesis about the chain fountain effect, best known as the Mould effect. I was intrigued by the explanations provided by Mehdi from ElectroBOOM and Steve Mould, so I decided to give it a try, as I wasn't satisfied with any of them.

In my view, the main problem from most explanations is to assume that the system is in a steady state, there is an significant influence from the dynamics of the waves that form as the chain is pulled out of the container, introducing fluctuations on the tension in the chain.

We need some more slow-mo footage to analyze and new experiments trying to suppress the wave formation.

Who's right? R: Neither
How does a chain fountain REALLY work? R: A theory about waves

Contents:
00:00 Intro
00:28 Mould effect
01:10 Whip effect
03:40 Wave start
05:25 Wave growth
07:34 Simulations

[FinFET]

In my view, the main problem from most explanations is to assume that the system is in a steady state, there is an significant influence from the dynamics of the waves that form as the chain is pulled out of the container, introducing fluctuations on the tension in the chain.
We need some more slow-mo footage to analyze and new experiments trying to suppress the wave formation.

[JohnDlugosz]

7:00 The guide can contain motorized wheels, not simply passive bearings. The speed can be matched to the chain speed, so it's essentially frictionless.
In addition, it can be used for additional experiments, pumping the chain upward, thus artificially providing a "kick".
By using two such motors, the other being on the downward run, you can regulate the speed rather than waiting for the equilibrium from the weight of the chain, force two ends of the chain to pass through constant points, and study how varying the forces at these two points causes waves, builds up the fountain, etc.

[leyline]

Mehdi already tried to show the whip effect. I think the whip is only part of the motion. The whip effect does not account for the rise of the fountain. The kickback force on the bottom as you showed at 2:20 is the force that gives rise.

[bencesarosi]

The perspective of having a stationary wave across a moving chain as opposed to a wave travelling across a stationary medium is brilliant!

[R.B.]

Something you sort of allude to with your description, accidentally or intentionally, and which I have not seen discussed elsewhere, is perhaps the sides of the container introduce a harmonic effect. If we follow your suggestion that the larger wave results from the constructive interference of smaller waves, perhaps the wall of the container acts somewhat like a fret board and it causes the noise of lots of waves of different frequencies to resonate more strongly at a frequency which contributes to the constructive interference.

[williamjg]

What if you put a motor on the bottom of the string and pull it faster than it could fall on it's own. Could the wave grow even taller than all of the experiments? Thoughts on this? And if so the height of the wave would depend on the speed of the sting. Both the unevenness of the string or the weight of the sting (for overcoming friction) would explain why some work and some don't.

[joeytheetge]

Thank you. The whip effect downward force acting with angler momentum. Like a whip.
A rotating object will speed up if you pull weight to the center or slow down if you bring the weight out. Or a sail boats sail at an angle with the wind will travel faster than the wind.
The chain effect is a force pulling the chain the angle is creating an opposing force creating lift.

[aniksamiurrahman]

Maaaan, its awesome. It would've been better if there was a written article for us ordinary folks in your website.

[martinstent]

Let’s go right back to when the chain starts to fall.
Imagine a link of the chain has bumped into the lip of the glass and rebounded so that the path of the chain forms a tight loop over the glass-lip. The centrifugal force inside that loop will force it to expand in diameter until the tension in the chain (centripetal force) balances out the centrifugal force of the chain loop. Now what happens as the chain speeds up? The tension in the chain stays relatively constant because it is determined by the weight of the small length of chain still inside the glass. But the centrifugal force will increase in proportion to the speed of the chain flying around the loop. The net centrifugal force is actually acting upwards, so the loop will rise up as the chain speed increases. It’s as simple as that. No magic involved.

[joebrandon]

What happens if you drop the container while the chain is falling?

[rhythmandacoustics]

Is it really waves? This reminds me of the slinky experiment in which if it was some sort of a spring fluctuating the beads should stay longer in the air.

[lucasb.r.j.]

obviously the effect is created because of the good old ancient magic, like many papers already concluded

[deang]

Great explanation. I feel all the explanations I have viewed so far haven't mentioned wave propagation until now. Instead of dampening the wave, excite it by vibrating the base of the cup at the same frequency as that acending wave. Will that increase the amplitude? Also are the balls spinning? The vibration and wave propagation could induce a spin. Is there a gyroscopic effect also adding to the amplitude? I have seen many people explain this effect, and it seem to me it's a combination of many

[sanjuansteve]

It's all about the centrifugal forces on the mass of the beads as they make their 180 degree turn. No?

[hankdewit]

I like your wave/whipping idea and waves traveling along the chain, but I think you need to take into account that the chain is also moving.

My take on it is as follows. The "stationary" wave at the top of the loop would be a progressive wave moving backwards against the flow of the links at exactly the same speed as the links. The speed v of a wave on the chain is, v = sqrt(T/lambda), where lambda is the mass per unit length and T is the tension in the chain. So the wave speed is proportional to the square root of the tension. I think the tension is maximum at the top of the chain. If we assume it's zero at the ground it would be near T = lambda * height * g at the top. That would give v=sqrt(g * height).

Elsewhere on the chain, the tension is lower, so the speed of the wave is lower and it would be carried away to the ground. At the beaker end, the lifting of the chain is a kind of unrolling effect requiring the chain to oscillate transversely (as you say) which generates waves. Waves traveling to the right get whipped away to the ground because they travel in the same direction as the links. The backward propagating waves drift slowly into the main loop as the tension on the left side is slightly less than in the loop itself. Once they are in the loop they stay as their speed is now matched by the tension. So you could imagine the loop as a "trap" for waves generated at the beaker.

[mategart]

Interesting new info and view about this topic

[KitagumaIgen]

The Cambridge-model is a completely steady-state model - they look at the situation where the falling end of the chain has already reached the ground. As such it is completely insufficient to model the dynamics of the effect...

[GermanTutorials]

That is exactly what i have been discussing with some guys on the r/physics subreddit! Its definitely a wave phenomenon, since one can clearly see the development of a standing wave. This implies that there have to be waves traveling back and forth in the linear medium. But i did not consider the amplification aspect of the two waves being in resonance with each other, explaining the raising fountain beautifully! I, as a fellow physicist, think you are right! Though, a rigorous analytic derivation of this effect is still missing.

[Richard-Freeman]

Atomic Shrimp put one out too, the day after yours. He had a similar idea with the waves.

[My_initials_are_O.G.cuz_I_am]

Whips effect doesn't increase the amount of force, it transfers it to a continuously smaller mass, whips get increasingly thinner and the bend radius decreases, so, through conservation of angular momentum, the tip velocity increases, you wouldn't get the effect with a consistent-width cord or rope, and since the chain fountain has a consistent angle, and a consistent linear density of chain, whip effect is impossible.