3B10.75 - Pendulum Waves

Push the Aluminum angle starter bar against the pendulum bobs so that they are all displaced by the same amount.  Quickly remove the bar and carefully watch the wave pass through various standing and traveling wave patterns before coming back to their initial mode in which they are all in phase.
The smaller unit made from fiber board and machine nuts as the pendulums is for use on the overhead projector.
Code Number:
3B10.75
Demo Title:
Pendulum Waves
Condition:
Excellent
Principle:
Wave Motion
Area of Study:
Acoustics
Equipment:
Multi-pendula wave demo, Aluminum angle starting bar.
Procedure:

Push the Aluminum angle starter bar against the pendulum bobs so that they are all displaced by the same amount.  Quickly remove the bar and carefully watch the wave pass through various standing and traveling wave patterns before coming back to their initial mode in which they are all in phase.  

The smaller unit made from fiber board and machine nuts as the pendulums is for use on the overhead projector.

References:
  • Xiangdong Feng, Changhong Lu, Jurgen Schulte, Zengxu Shan, Gentong Liu, "Pendulum Waves: A Model of Thomae's Function", AJP, Vol. 91, #12, Dec. 2023, p. 964.  
  • James A. Flaten, Kevin A. Parendo, "Pendulum Waves: A Lesson in Aliasing", AJP, Vol. 69, # 7, July 2001, p. 778.
  • Richard Berg, "Pendulum Waves: A Demonstration of Wave Motion Using Pendula", AJP, Vol. 59, # 2, February 1991, p. 186.
  • Bobby Mercer, "Swinging Wave Machine", Junk Drawer Physics, p. 63. 

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.