A Closed Form Solution of the Run-Time of a Sliding Bead along a Freely Hanging Slinky

  • Haiduke Sarafian
Part of the Lecture Notes in Computer Science book series (LNCS, volume 3039)


The author has applied Lagrangian formalism to explore the kinematics of a bead sliding along a frictionless, freely hanging vertical Slinky. For instance, we derived a closed analytic equation for the run-time of the bead as a function of the traversed coil number. We have applied Mathematica to animate the 3-dimensional motion of the bead. The derived run-time is incorporated within the animation to clock the bead’s actual motion. With the help of Mathematica we have solved the inverse run-time equation and have expressed the traversed coil number as a function of the run-time. The latter is applied to further the analysis of the problem conducive to analytic time-dependent equations for the bead’s vertical position, its falling speed and its falling acceleration, and its angular velocity about the symmetry axis of the Slinky. It is also justified that a Slinky is a device capable of converting the gravitational potential energy of a sliding bead into pure rotational energy.


Angular Velocity Symmetry Axis Closed Form Solution Gravitational Potential Energy Maximum Angular Velocity 
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Copyright information

© Springer-Verlag Berlin Heidelberg 2004

Authors and Affiliations

  • Haiduke Sarafian
    • 1
  1. 1.The Pennsylvania State UniversityYorkUSA

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