Our favorite demonstration for sound waves is to set up a compressional pulse on a horizontally stretched Slinky™. One can easily watch the pulse move back and forth at a speed of the order of one meter per second. Watching this demonstration, it occurred to us that the same thing might happen in a steel pipe if you hit the end of the pipe with a hammer. The main difference is that the speed of sound in steel is close to 5000 meters per second. If you hit the end of a 10-ft (3.05-m) pipe, the pulse should take about 1.2 ms to go down and back, a time conveniently measured by an oscilloscope.
REFERENCES
1.
Gerald P.
Hart
, “Measurement of the speed of sound in metal rods using the microcomputer
,” Phys. Teach.
24
, 89
(Feb. 1986
).2.
Tony
Key
, Robert
Smidrovskis
, and Milton
From
, “Measuring the speed of sound in a solid
,” Phys. Teach.
38
, 76
–77
(Feb. 2000
). A signal generator and a transducer were used to create a series of square wave pulses in an acrylic rod.3.
David
Potter
, “The speed of sound in an iron rod
,” Phys. Teach.
40
, 56
–57
(Jan. 2002
). A pickup coil used to detect the enhanced magnetization of the compressional pulse.4.
Karl C.
Mamola
, “Measurement of sound velocities in metal wires
,” Am. J. Phys.
42
, 1117
–118
(Dec. 1974
). A loud compressional wave is created by dragging a wet sponge along a stretched wire.5.
Elisha
Huggins
, “Fourier analysis in introductory physics
,” Phys. Teach.
45
, 26
–29
(Jan. 2007
). Introduces the use of MacScope.6.
The iMic is discussed at: http://www.griffintechnology.com/products/imic.
7.
The shareware program MacScope II, which turns any USB Mac or Windows computer into an audio oscilloscope, can be freely downloaded from: http://www.physics2000.com.
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© 2008 American Association of Physics Teachers.
2008
American Association of Physics Teachers
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