Falling Chain

[ken_roberts]

Yesterday I ran across a really neat paper, about the velocity and weight of a chain which is falling onto a scale. Now you might think it is obvious, the chain falls at the free fall rate due to gravity, but not so - it falls faster! Moreover, the weight on the scale is more than prior theory predicts

Comments

Doh... and problem solved, you'll need your calculator :)

[torpidai]

Finaly started to read about the chain experiment, just as soon as it dawned on me, no need to download PDF's anymore :S

anyhaps... For example, consider a chain attached by its two
ends at the same height and separated horizontally by a certain distance [see Fig. 1(b)]. As
one of the ends is released the acceleration of the chain tip is greater than g, the acceleration
due to gravity.2-4

Why is this any great surprise? as one end of the chain is "Fixed" the friction will never be equal in all links of the chain, (even a greased bicycle chain as I've previously suggested I'd use for such experiments.) but anyhaps, the rate of fall, I'd suggest, due to gravity, will, on links nearer the fixed end, be "wasted" on neglible heat due to friction of the links, the chain itself will be "trying", initialy to fall downwards, through a line plotted directly through it's centre f gravity (One would assume this would be the center of the chain) but no matter what type of release mechanism used (even electro-magnetic) there will be some friction drag at it's release, starting the "Whipping effect" chain (no pun intended) reaction.

As now the end of the chain has 2 forces upon it, 1) gravity and 2) An angular force in the general direction of the rest of the chain, as soon as the chain sections drop far enough to take up any slack in the joints, that loose end will be whipped round in an arc, slapping whatever is in it's way.

I'm actually pretty sure It could be modelled pictorialy with a few lines of code, but as I've still not finished a programming project I promissed a friend for her charity by last Xmas, It'd be safer not to be seen working on another :)

I told you that set of scales was a bad idea ;) It should well be "All in the math", IMHO poor experimentation and publication of it has caused people to doubt the science we were all taught in school.

I'd offer to assist, but you've seen the state of my math these days, though I'm sure it'll all work out to be a nice little formula dependent upon length of chain, (Radius of arc), co-efficient of friction in eac of the chain links, amount of friction exerted by the release mechanism upon release, a little (but probably not negligable) amount of resistance from the medium experiment performed in (Here air, but as I suggested, I'd try it in oil to slow it all down and use the really slow cheap crappy cameras I already own).

Now when are you going to do the math? and do I get my name "In lights" when you've "done the math"? hehe

Tis "just a theory", after reading a little of the ball drop conclusion I switched off, too tired at this time of night and looking up every other word because my scientific vocabulary is abysmal, made me remember why I don't regularly read papers, nor even new scientist any more.