3A95.70 - Variable Length Pendulum - Swing - Pump a Swing

Code Number:
3A95.70
Demo Title:
Variable Length Pendulum - Swing - Pump a Swing
Condition:
Excellent
Principle:
Potential to Kinetic Energy, Simple Harmonic Motion
Area of Study:
Acoustics

Disclaimer

Equipment:
Variable length pendulum, variable length pendulum with aluminum bar and bearing supports.
Procedure:

The variable length pendulum makes use of a plastic bushing at the pivot point to make the pendulum length variable while the pendulum is swinging. This is often used to demonstrate subtle points.

The variable length pendulum with bearing supports is a more stable system designed to withstand the forces of the swinging pendulum.  This needs to be set up on one of the little tables that has the rod supports and the proper distance.  Even then if the pendulum is given enough energy the whole table will visibly move when the length of the pendulum is varied.

References:
  • Ann-Marie Pendrill, "Serious Physics on a Playground Swing - With Toys, Your Own Body, and a Smartphone", TPT, Vol. 61, #5, May 2023, p. 355.
  • Klaus Bickel and Robert Denschlag, "Playground Physics: What Happens When Trying a 360° Swing?", TPT, Vol. 57, #3, Mar. 2019, p. 146. 
  • T. Wickramasinghe, and R. Ochoa, "Analysis of the Linearity of Half Periods of the Lorentz Pendulum", AJP, Vol. 73, #5, May 2005, p. 442.
  • William B. Case, "The Pumping of a Swing From the Standing Position", AJP, Vol. 64, #3, Mar. 1996, p. 215.
  • William B. Case and Mark A. Swanson, "The Pumping of a Swing from the Seated Position", AJP, Vol. 58, #5, May 1990, p. 463.
  • Stephen M. Curry, "How Children Swing", AJP, Vol. 44, #10, Oct. 1976, p. 924.
  • John T. McMullan, "On Initiating Motion in a Swing", AJP, Vol. 40, #5, May 1972, p. 764.
  • Bryan F. Gore, "Starting a Swing from Rest, "AJP, Vol. 39, #3, March 1971, p. 347.
  • Joseph A. Burns, "More on Pumping a Swing", AJP, Vol. 38, #7, July 1970, p. 920.
  • Bryan F. Gore, "The Child's Swing", AJP, Vol. 38, #3, Mar. 1970, p. 378.
  • A. E. Siegman, "Comments on Pumping on a Swing", AJP, Vol. 37, #8, Aug. 1969, p. 843.
  • Peter L. Tea, Jr. and Harold Falk, "Pumping on a Swing", AJP, Vol. 36, #12, Dec. 1968, p. 1165.
  • Jearl Walker, "1.115, The Pendulum in the Pit", The Flying Circus of Physics Ed. 2, p. 57.
  • Jearl Walker, "1.113, Pumping Playground Swings", The Flying Circus of Physics", p. 56.
  • Jearl Walker, "1.114, Incense Swing", The Flying Circus of Physics", p. 56.
  • Ron Hipschman, "Pendulum Table", Exploratorium Cookbook III, p. 188.1 - 188.18.

Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.