MadSci Network: Physics

Re: Why do certain frequencies cause more reactive vibrations than others?

Date: Tue Jun 22 15:49:09 1999
Posted By: John Balbach, Post-doc/Fellow, Physics, National Institutes of Health
Area of science: Physics
ID: 928535999.Ph

Sometimes it is possible to excite the natural frequencies of a particular 
object or space.  One favorite way is to apply sound waves at the frequecy 
that the object or space would respond to.  The natural frequency of an 
object has a lot to do with the material it is made of and its shape.

This phenomenon is most obvious with tuning forks, but buildings, rooms, 
the sun and many other objects also have natural frequencies at which they 
will tend to vibrate.

For a room, these frequencies will tend to be low, but still within the 
range of the human ear.  A good way to get at the natural frequency of a 
space is to compare the wavelength of the note in air with the dimensions 
of the space.  A low "G" note has a wavelength of about 7 feet.  Higher 
frequencies have shorter wavelengths, and would not resonate with a large 
space.  Even lower frequencies need larger spaces to resonate, but a room 
is a conveniently lower-register sized space.

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