( ( (astounding sound) ) )

(((((Astounding Sound)(Astounding Sound)))))

Steven Berger

Orefield Middle School

8th Grade

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Problem StatementProblem Statement

At what column height does sound resonate in a

cylinder of air and water? Will changing the density of a liquid change the speed of sound

through that liquid?

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HypothesisHypothesis

If the speed of sound in an air and water column can be established by finding its

natural resonance, changing the density of the water (ex. saturating it with salt) will

decrease the speed of sound. According to research, sound travels slower through denser materials because there are more molecules for the sound waves to vibrate.

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ResearchResearch• Sound Wave: A pressure disturbance that travels

by particle-to-particle interaction.

• Frequency: Number of times an object vibrates per second.

• Tuning Fork: A fork shaped acoustic resonator.

• Natural Frequency: When the air column vibrates at the same frequency as the tuning fork.

• Resonance: When an object vibrating at or near the natural frequency of a second object causes it to vibrate.

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Research (cont.)Research (cont.)The tuning fork forces

sound waves into the top of the tube. If the air

column’s natural resonance matches that

of a tuning fork, the sound will get louder and

produce a fundamental.

Add or decrease water in the tube to find the natural resonance of the air column.

Vibration: The complete back and forth motion of an object.

Fundamental: The lowest frequency that an air column will resonate at.

Forced Vibration: When an object forces another into vibration.

For the fundamental, only ¼ of the wavelength goes into the column.

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MaterialsMaterials• set of Tuning Forks/with Striker• plastic tube 5.08cm x 91.44cm• tap water 2L• table salt 340 grams• sugar 340 grams• distilled water 1 ½ L.• magnesium sulfate 453 grams• plexiglass 16 x16 cm thick• gorilla glue• funnel• 4 x 9 x 61 cm wood• 1 x 122 cm flexible tube• masking tape• wood screws

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Procedure for Assembling CylinderProcedure for Assembling Cylinder

1. Cut tube down to 61 cm.2. Drill holes in plexiglass3. Glue 61 cm tube to the

plexiglass base.4. Glue flexible tube to other side

of plexiglass base.5. Put strip of masking tape on

tube and mark off centimeters.6. Attach completed cylinder to

wood base.7. Insert funnel into flexible tube.

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1. Pour the liquid you are going to test into the funnel.2. Add or remove water until the desired air column

height is reached.*3. Strike & hold a tuning fork over the top of the plastic

column.4. Raise or lower the funnel (to change the water

column height) until the sound of the tuning fork becomes the loudest.

5. Record the air column height in cm.6. Repeat the whole procedure again testing different

liquids with different densities.7. Calculate the speed of sound.

Procedure for Testing LiquidsProcedure for Testing Liquids

*most fundamentals occur between 18-33 cm

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Calculating the Speed of SoundCalculating the Speed of Sound The formula for speed of sound is V=4F(L +0.4d)

V is the speed of sound in air column

F is the frequency of tuning fork

L is the length of the air column in meters

D is the diameter of the tube in metersSample Calculation: (D/288 Tuning Fork)

V= 4•288(.28+0.4•.0508)

V=1024(.28+.02032)

V= 1152•.30032

V=345.97 m/s

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Data/GraphsData/Graphs

This graph shows the fundamentals of my control group, tap water. As the tuning fork frequency decreases, the fundamental column height gets

longer. (Note column heights shown are proportionate to actual testing.)

15 16 18.75 21 23.5 25 28 32

0

10

20

30

40

50

60

70

Co

lum

n H

eig

hts

in

CM

C/512 B/480 A/426.6 G/384 F/341.3 E/320 D/288 C/256

Note/Tuning Fork

Fundamentals

water air column

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This graph shows the speed of sound for my control group tap water. Most speeds are within 1.5% of the theoretical speed of sound. The researcher multiplied .6 by the temperature and added 331 to find theoretical speed or sound. (V=331+.6T)

Formula for speed of sound: V=4f(L+.4d)

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This graph shows the speed of sound for all the liquids categorized by tuning fork and density.

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ConclusionConclusion• The original hypothesis was incorrect in

thinking that changing the density of water would affect the speed of sound.

• The sound waves that caused a resonance did not go to the bottom of the tube and back. They went to the bottom of the air column and back when the tuning fork goes through one vibration.

• When the frequency of the tuning fork matches the height of the air column the fundamental occurs.

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Conclusion (cont.)Conclusion (cont.)• Benefits: People who design instruments might want to

know the fundamental of a note so they know how to design the instrument. Architects might benefit because they need to know how sound travels in open spaces. Sound waves are also being used to treat people with tremors.

• Areas to Improve:Develop a way to strike the tuning fork the same way for each trial.Be more careful holding the tuning fork in the same place for each trial.

• For further study: To extend this experiment the researcher could try tuning forks with higher and lower frequencies and try other diameter columns.

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Resources/BibliographyResources/Bibliography• Rahn, Joan Elma. "Chapters 1-2." Ears, Hearing & Balance.

New York: Atheneum, 1984. Print.• "Sound." The New Book of Popular Science. Vol. 3. Danbury,

CT: Scholastic Library Pub., 2008. 198-208. Print.• Silver, Jerry. 125 Physics Projects for the Evil Genius, The

Speed of Sound Resonance in a Cylinder, New York: McGraw-Hill, 2009. 188-90. Print.

• "Sound Is a Mechanical Wave." Sound Waves and Music – Lesson 1 The Nature of a Sound Wave. The Physics Classroom. Web. 27 Oct. 2011. <http://www.physicsclassroom.com/Class/sound/u11l1a.cfm>.

• "Resonance." Sound Waves and Music Lesson 5, Musical Instruments The Physics Classroom. Web. 27 Oct. 2011. <http://www.physicsclassroom.com/Class/sound/u11l5a.cfm>.