# Falling chain

Thanks to reader Tadas, I saw this fascinating clip about falling chains.

I don’t fully understand the explanation because I haven’t worked out the theory myself.

But it is fun to watch.

1. Rob Grigjanis says

The chain isn’t just ‘dropped’ out of the jar. He gives it a good downward yank at the beginning. That’s when I stopped watching. And I think the links between beads have to be rigid, so that the initial momentum from the downward yank is efficiently transferred to upward momentum of the part of the chain inside the beaker, in a lever-like effect.

2. Rob Grigjanis says

By ‘rigid’, I mean not having much deformation over the length of a link.

3. Pierce R. Butler says

But, but… I can’t argue with the model that the chain produces a rod-like effect that pushes energy upwards into the part of the chain already in motion, though I would like it explained in more detail.

Howsomeverwise, as shown, the chain rises from a loose heaping of more chain -- not the flat rigid surface used to illustrate the purported mechanism. Why doesn’t the reaction energy dissipate itself into that chaotic but seemingly energy-absorbent mass rather than push upward?

Also, the demonstration cries out for more detailed close-ups -- the presenter even leaves his hand over the remaining chain during both exhibitions. I don’t think this is a hoax sponsored by the powerful but mysterious light ball-chain industrial complex, but the video apparent amateurishness does raisemy suspicions.

4. flex says

Rob,

The solution to your observation would be to take a very long length of beads (I hesitate to call it a chain, because it appears to me that the amount of angular movement allowed between individual beads is probably an important factor), long enough for some of it to extend already to the floor, and let it go under it’s own weight.

If the explanation is correct, even under those conditions the string of falling beads would rise above the lip of the container.

It seems to me that if the explanation is correct, you would also see a small change in thermal energy at the base of the container. If I remember my thermodynamics properly, if the beads are gaining energy by using the normal force, you would see a small drop in temperature. But it’s been a really long time since my thermodynamics courses.

5. blf says

There is a type of chain ferry which operates in roughly the manner hinted at. The chain is secured at both ends on opposite sides of the river. The chain normally lies flat on the riverbed. The ferry contains one toothed wheel, through which the chain is fed. To start, the wheel is set spinning in the desired direction. From then on, the ferry propels itself across the river (no motor required). The trick, as I now recall, is the “intake” chain leading from the riverbed to the ferry’s toothed wheel in the direction of travel is essentially vertical, whilst the “exhaust” chain gently slopes back down to the riverbed. Hence, there is more unsupported chain weight in the “exhaust” than the “intake”, causing the wheel to turn in the desired direction.

There are multiple types of chain ferrys. Some have motorised wheels, some (rarer nowadays) have hand-cranked wheels, and so on. There is(? was?) at least one example of the (very rare?) type I attempted to describe someplace in teh “U”K, but I now cannot recall where or it’s name — Sorry !

6. Rob Grigjanis says

Hard to ignore the similarity between this and a siphon.

7. Rob Grigjanis says

John, yes, but that’s less fun than thinking about it.

8. Tethys says

I can confirm that the bead garland arched itself several inches above the edge of my holding container. It works better when dropped from the second floor (12 feet) than it did when dropped from five feet.

9. flex says

blf wrote,

There is a type of chain ferry which operates in roughly the manner hinted at.

Huh. There is a chain ferry in Saugatuck, MI. Although it’s not clear if it’s propelled in the manner in which you say. But we’ve stayed in Saugatuck, and we’ve thought of going back sometime. There’s a couple nice little B&Bs there. Not cheap, as close as it is to Chicago, but not out of our budget range. If we go back, we’ll have to make a point to ride the chain ferry.

Thanks for peaking my interest.

10. flex says

Dammit,

“piquing my interest”. I should know better.

11. blf says

flex@10, Saugatuck Chain Ferry indicates that one is the rare hand-cranked type: “It is hand propelled! The operator turns a crank on the inside and this pulls the ferry along the chain.”

I apologise for not providing any references for the very rare type I attempted to describe… which is frustrating, as I learned about that type based, in part, on a diagram showing how it worked (in the context of a discussion about the various types of chain ferrys). Whilst I vaguely recall the forum, searches have gone nowhere. Grrrrrr…

12. DonDueed says

I’m not buying the explanation (for the reason Pierce R. Butler outlined in #3).

Rather, this is the first clear evidence that we live in a simulation. Obviously, some junior coder got assigned to work on the beaded-chain subroutine, and they made a sign error someplace.

13. Malcolm says

As with Mr Griganis to me this is just a siphon effect and the chain comes out as it does due to the stiffness of the links. The energy for this being the change in potential ebnergy in the chain.

14. says

Each time the end of the chain left the beaker, I couldn’t help but be disturbed by his lack of safety glasses.

15. DonDueed, 13

Obviously, some junior coder got assigned to work on the beaded-chain subroutine, and they made a sign error someplace.

Which is why we have some pretty awesome any% ball-chain glitch speedruns of reality.