Chain fountain (Mould effect)
Why does a chain of beads poured out of a beaker rise up in an arc above the rim before falling, as if pulled up by an invisible force?
History and references
Settled in 2014 by John Biggins, Mark Warner (University of Cambridge).
YouTuber and physicist Steve Mould popularized the startling 'chain fountain' in 2013, initially proposing his own (incorrect) explanation involving the chain locking together in the container. Cambridge physicists John Biggins and Mark Warner formalized the problem in 2014, showing mathematically that as each link is yanked from the pile, a reaction force pushes it upward beyond what simple momentum transfer would predict, and this extra 'pick-up' force is what holds the arc up above the beaker's rim. Follow-up papers (e.g. Hanna 2018, and later 'reexamining the chain fountain' studies) have refined and debated the precise microscopic origin of this extra force, but Biggins & Warner's basic account of an anomalous upward force at pickup is the widely credited resolution.
A toy-store bead chain, poured out of a pot, reveals a genuine and previously unrecognized force in classical mechanics.
Explanations that circulated
- Steve Mould's own initial on-camera explanation (that the effect was due to the chain's links locking/interlocking in the pot) was shown by Biggins & Warner to be incorrect; the real driver is an extra upward force generated as each link is picked up from the pile, related to the chain's finite rigidity/bead spacing.
References
- Understanding the chain fountain, J. S. Biggins, M. Warner, Proceedings of the Royal Society A, 2014
Solutions 0
Sign in or create an account to publish a solution