The surprising dynamics of a chain on a pulley: Lift off and snapping

P. T. Brun, Basile Audoly, Alain Goriely, Dominic Vella

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


The motion of weights attached to a chain or string moving on a frictionless pulley is a classic problem of introductory physics used to understand the relationship between force and acceleration. Here, we consider the dynamics of the chain when one of the weights is removed and, thus, one end is pulled with constant acceleration. This simple change has dramatic consequences for the ensuing motion: at a finite time, the chain 'lifts off' from the pulley, and the free end subsequently accelerates faster than the end that is pulled. Eventually, the chain undergoes a dramatic reversal of curvature reminiscent of the crack or snap, of a whip. We combine experiments, numerical simulations and theoretical arguments to explain key aspects of this dynamical problem.

Original languageEnglish (US)
Article number20160187
JournalProceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences
Issue number2190
StatePublished - Jun 1 2016
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General Engineering
  • General Physics and Astronomy
  • General Mathematics


  • Atwood machine
  • Curvature-reversal
  • Dynamic contact mechanics
  • Strings and chains
  • Whip


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