“Resonant frequency of glasses based on shape”
By Morgan Johnstone
James Stallkamp
Fabianny Anez
· Method
· Results
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The idea of “playing glasses” was popularized by Richard Pockridge and Christoph Gluck in the 1700’s, but were known about and played before then (http://www.glassarmonica.com/index.php). Evidence of glass instruments exist from as early as the 1400s (http://www.glasmusik.com/diven.htm ).The original instrument that was made of just wine glasses is now referred to as the glass harp. Benjamin Franklin brought more fame to glass instruments by making his glass harmonica, which consisted of bowls that spun on a rod (http://glassharp.eu/pdf/PLAYED_ON_THE_GLASS.pdf ). The science of such instruments is thus: by placing your finger on the rim of the glass, while pressing and moving it at certain pressures and speeds, the vibration of this causes the molecules to vibrate at their certain frequency (Giancoli, 1980). Adding water tunes the frequency, making it go lower because the vibration of the glass is slowed. The glasses can also be tuned by make: thicker and thinner walls of the glass affect its pitch by increasing or decreasing the speed at which the glass can vibrate (http://www.pbs.org/safarchive/4_class/45_pguides/pguide_804/4484_franklin.html and http://glassharp.org ). Controlled variables were temperature, type of fluid added, and the material of the glasses. The independent variable was the amount of water added to the glasses. Dependent variable was the frequency of the note produced. The purpose of our lab is to see if the shape of the glass affects the frequency when water is added to the glass. Our hypothesis is that the graph of the water will be linear for glasses that don’t change shape (such as a champagne glass) and parabolic for those that change shape in an outward/inward fashion (a larger wine glass). This will happen because you will only have to add the same amount of water every time for the glasses that don’t change shape, but for glasses that change shape outwardly you will have to add more water every time to increase the note by one step.
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· Five different types of glasses with a stem
· Water
· Tuner
· Your finger
· Graduated cylinder
· Pencil and paper for gathering data
To begin with, pick one of the glasses and put one hand on the base of the glass. Then wet your finger and run your finger along the rim of the glass while varying speed and pressure until you find the resonant frequency. When you find the right frequency the glass will emit a clear, ringing sound. Measure the ringing sound with the tuner. Record the note name and how flat or sharp in cents it is. Measure out a certain amount of water in a graduated cylinder and add it to the glass (the amount varies; for larger glasses use larger amounts and vice versa. Aim for an amount that you can get many data points from), run your finger around the rim to get the ringing sound, and record the note name and how sharp or flat in cents it is once again. Continue this process, adding the same amount of water every time, until you can no longer add water to the glass or if you can’t get a clear sound. Empty the glass and clean. Repeat the procedure with the four other types of glasses.
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.:. text data .:.Excel data
Hz +or- .0005
mL +or- .5
Summary of Results: Our results showed the frequency got lower as more water was added. The frequency changed very little at first and then as more water was added it changed at a much larger rate. The starting frequency was high for smaller glasses and lower for larger ones. It took less water to change the frequency in smaller glasses and more in larger ones which suggests that frequency changes with percentage of volume filled with water. Note: the error was so small that it could not be represented on the graph.
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Our results showed the frequency got lower as more water was added. The frequency changed very little at first and then as more water was added it changed at a much larger rate. The starting frequency was high for smaller glasses and lower for larger ones. It took less water to change the frequency in smaller glasses and more in larger ones which suggests that frequency changes with percentage of volume filled with water. Therefore, our hypothesis was incorrect. This is because frequency changes in relationship to percentage of the glass filled, rather than the shape of the glass. This is probably because as the glass becomes fuller, the part of the glass that is in contact with the water vibrates differently than the glass that is not submerged. One main source of error was our measuring device, because it wasn’t very accurate. Another one was that the amount of water may have changed because of the way the glass had to be played; a finger had to be dipped in water in order to “play” the glasses. Some improvements that could be made to our procedure were a better measuring device, a tuner that directly measured in hertz, and if we had access to several sizes of the same shape of glass.
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Glassarmonica.com (2000) Zeitler, William. Home page. Retrieved November 8, 2010 from http://www.glassarmonica.com/index.php
Glasmusik.com (no date) Himler, Martin and Furbacher, Beate. Home page. Retrieved November 8, 2010 from http://www.glasmusik.com/diven.htm
NO INFORMATION Retrieved November 8, 2010 from http://glassharp.eu/pdf/PLAYED_ON_THE_GLASS.pdf
www.pbs.org(2000) Scientific American Frontiers. Retrieved November 8, 2010 from http://www.pbs.org/safarchive/4_class/45_pguides/pguide_804/4484_franklin.html
Glassharp.org (2010) Brien Engel. Home page. Retrieved November 8, 2010 from http://glassharp.org
Giancoli, Douglas C.: Physics Fifth Edition. New Jersey, Prentice Hall 1980
Annotated Links
http://www.glassarmonica.com/index.php - this site was used for learning about history of the glass harmonica
http://www.glasmusik.com/diven.htm - this site was used for history of the glass harmonica as well
http://glassharp.eu/pdf/PLAYED_ON_THE_GLASS.pdf - this site was used for construction of the glass harmonica, as well as history
http://www.pbs.org/safarchive/4_class/45_pguides/pguide_804/4484_franklin.html - this site was used for information on how it actually works
http://glassharp.org/ - this site was used for more science and a tad more history