Bend a Wall

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 Code Number :   1H10.35



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.

Condition :   Good   
Principle :   Action & Reaction  
Area of Study :  Mechanics  
Equipment :   Laser, beam splitter, Radio shack speaker amplifier with photocell, mirror with magnetic backing, metal "wall".

Procedure :   Attach the magnet to the blackboard or metal wall.  Align the laser beam so that it is bounced back into the laser. Place the beam splitter in front of the laser and put the reflected beam onto the photocell.  Turn up the amplifier and then press on the wall or the table holding the apparatus.  A squeal should emit from the amplifier speaker as the wall or table flexes.

An simple version of this demo is to just shoot the laser beam directly into the photocell that is connected to the amplifier/speaker.  Place a microscope slide in the beam between the laser and the photocell.  As you rotate the microscope slide a "whine" will be heard from the speaker.

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Chris R. Brown, "Optics Puzzler", TPT, Vol. 45, # 9, Dec. 2007, p. 571.

James M. Moses, K. P. Trout, "A Simple Laser Microphone Classroom Demonstration", TPT, Vol. 44, # 9, Dec. 2006, p. 600.

Daniel L. Maclsaac and Michael Nordstrand, "Wall Fexture Correction", TPT, Vol. 23, # 6, Sept. 2001, p. 325.

Daniel L. Maclsaac and Michael Nordstrand, "Demonstrating and Measuring the Flexure of a Masonry Wall", TPT, Vol. 39, # 4, Apr. 2001, p. 212 - 214.

Tung Jeong, Larry Alofs, "Hear the Wall Bend", TPT, Vol. 23, # 2, Feb. 1985, p. 108 - 110.


Borislaw Bilash II, David Maiullo, "Push You, Push Me", A Demo a Day: A Year of Physics Demonstrations, p. 117.

Borislaw Bilash II, David Maiullo, "Lazy Walls", A Demo a Day: A Year of Physics Demonstrations, p. 6.

Richard E. Crandall, "Simple and Vivid Demonstrations of Advanced Concepts in Physics", The Amateur Scientist, Jan. 1983.

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