Tuning Fork Physics

A tuning fork consists of  a stem and two prongs and is constructed from aluminum alloy.
A tuning fork consists of a stem and two prongs and is constructed from aluminum alloy. | Source
Tuning forks come in a range of frequencies which correspond to notes in an octave.
Tuning forks come in a range of frequencies which correspond to notes in an octave. | Source

By Joan Whetzel

Tuning forks, most often remembered for aiding in instrument tuning, have other uses in the holistic health industry as well as in scientific research. But each tuning fork must be made of the right materials, tuned correctly, and produce the purest tone to be useful.

What Are Tuning Forks?

Tuning forks were invented by British musician, John Shore, in 1711. These y-shaped gadgets produce a clean sound when lightly rapped against a hard surface. The sound it produces that vibrates at a steady, acoustic frequency, which is what has made it popular in the music industry for tuning instruments. Nowadays, tuning forks are used in other industries as well.

Police departments, for instance, use them to calibrate their radar guns used for controlling traffic speeds. In the medical arena - especially the holistic aspects of medicine and psychology - the vibration produced by tuning forks when placed against the bones can identify the location of fractures. They have also been employed to alter the brain's biochemistry, which has applications that include dream work, stress relief, and left- and right-brain thought pattern management. Tuning forks are also used in acoustic science research, especially for tuning or calibrating the devices used to perform the experiments in this field. For acoustical research, the tuning forks must be tuned accurately to within +/- 0.05Hz based on the C256 to C512 so that they deliver the exact pitch representing the progression of an octave.

Air molecules surround the tuning fork inside and out while the fork is not vibrating.
Air molecules surround the tuning fork inside and out while the fork is not vibrating. | Source
When the prongs vibrate outward the air molecules clump together outside the prongs (compressed wave).
When the prongs vibrate outward the air molecules clump together outside the prongs (compressed wave). | Source
When the prongs vibrate closed, most of the air molecules stay close to the prongs, leaving some of the air molecules at a distance from the tuning fork (rarefaction wave).
When the prongs vibrate closed, most of the air molecules stay close to the prongs, leaving some of the air molecules at a distance from the tuning fork (rarefaction wave). | Source

How Tuning Forks Work

Each tuning fork is tuned to a specific frequency - or simple harmonic oscillation - producing its own note on the musical scale when struck. Good tuning forks are constructed from a special metal alloy (steel doesn't work) that can produce the characteristic ringing sound for a few minutes. Today's tuning forks are usually made from some form of a hard aluminum alloy. The exact pitch, or frequency, is established by the prong length.

At rest, the prongs are surrounded by air molecules, inside and outside of the y-shaped prongs. When struck against a surface, the tuning fork's two prongs vibrate toward and away from each other. This forces most of the air molecules to move to the outside of the prongs, crowding together and bumping into each other as the prongs move apart (compression wave). Most of the air molecules move back inward with the prongs as they come back together, leaving an area with less air molecules (rarefaction wave). The audible sound waves is made up of a series of thse compression and rarefaction waves

The handle vibrates in a small, up-and-down motion. The small amount of vibration in the handle allows it to be held without appreciable loss of sound. The handle can also be used to intensify the sound by placing it on a hard surface that resonates; with a hollow wood box being the best conductor of sound.

Each tuning fork's frequency (in Hz, or cycles per second) corresponds to a note within a  musical octave.
Each tuning fork's frequency (in Hz, or cycles per second) corresponds to a note within a musical octave. | Source

Tuning Fork Pitch Frequency

Tuning fork frequency is based on factors such as the density of the material from which the fork is made, the radius of the prongs as well as their length, and the measurement of the stiffness of the tuning fork. The first tuning fork invented by John Shore had a pitch of A423.5, which represented the note "A" vibrating at a frequency of 423.5Hz (cycles per second). Today's orchestras tune to a universal frequency of either A440 or C523.3 which makes it possible for the musicians to play together without sounding out of tune. A tuning fork is frequently used to set the pitch, though pitch pipes and electronic tunic forks may also be used.

For some interesting grade school science projects involving the use of tuning forks visit this website:

Science Projects

http://scoilchaitrionajnrscience.blogspot.com/2008/06/sound-investigations-with-tuning-fork.html

And for Middle School Science Projects, visit:

Tuning Fork Lab

http://www.middleschoolscience.com/tunefork.htm

Bibliography

Pickover, Clifford A.. The Physics Book. New York: Sterling Publishing, Inc., 2011.

Online Tuning Forks. Tuning Forks. Downloaded 2/4/2012.

http://www.onlinetuningfork.com/

Tools for Wellness. Tuning Forks for Sound Therapy. Downloaded 2/4/2012.

http://www.toolsforwellness.com/tuning-forks.html

Harvard University. Tuning Forks. Downloaded 2/4/2012.

http://www.fas.harvard.edu/~scdiroff/lds/OscillationsWaves/TuningForks/TuningForks.html

Indigo Instruments. Scientific Tuning Forks. Downloaded 2/4/2012.

http://www.indigo.com/tuning/scientific-tuning-forks.html

The Franklin Institute. The Science of Sound. Downloaded 2/4/2012.

http://www.fi.edu/fellows/fellow2/apr99/soundsci.html

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