3B22.10 - Standing Waves in a String - Hanging Motor

Code Number:
3B22.10
Demo Title:
Standing Waves in a String - Hanging Motor
Condition:
Excellent
Principle:
Standing Waves on a String.
Area of Study:
Acoustics
Equipment:
Motor with battery pack on a fishing swivel, bright colored string.
Procedure:

Start the motor and let it hang from the end of the string.  Adjust the length of the string until standing waves are visible.  Up to seven nodes should be obtainable. 

NOTE:  The motor must be balanced around the center of mass for this to work well.

References:
  • Imelda S. Caleon, R. Subramaniam, "Exploring Students' Conceptualization of the Propagation of Periodic Waves", TPT, Vol. 48, # 1, January 2010, p. 55.
  • Alison Hapka, "Handheld Standing-Wave Generator", TPT, Vol. 38, #6, Sept. 2000, p. 342.
  • W-122, "DC Motor on String", DICK and RAE Demo Notebook.
  • Don Rathjen, Paul Doherty, "String Machine", Square Wheels, 2002, p. 119.
  • Borislaw Bilash II, David Maiullo, "Standing Wave Generator", A Demo a Day: A Year of Physics Demonstrations, p. 210.
  • Arbor Scientific, "Simple, Inexpensive Standing Wave Kits Get The Entire Class in on The Act", p. 2.
  • Chris Chiaverina, "Inexpensive Standing Wave Apparatus", The Newsletter of the Wisconsin Association of Physics Teachers, Number 8, March 1999.

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.