Speed of Sound:  Mach 1Mach1 cylinder
Obj: Determine the speed of sound using resonance.

Materials: 500 mL G.C., tuning forks, resonance tube

1. Fill the 500 mL graduated cylinder (gc) completely full. Record the air temperature in your area.
2. Record the frequency / stamped on the tuning fork.
3. Using a vernier caliper, record the diameter of the resonance tube. Place the resonance tube into the gc.
4. Strike the tuning fork with the rubber mallet, then locate the maximum amplitude (loudest volume) by adjusting the height of the resonance tube in the gc. This will take several trials to find the exact height above the water level.
5. Record the distance above the water level to the top of the resonance tube.
6. Repeat for two other tuning forks.

Analysis (for each tuning fork)
1. Add to the distance measured above the water level in Step 4-5 the following:
            0.4 x diameter of the resonance tube.
Be careful of units. This adjusted distance will be λ. ___________m
2. Calculate the λ and then the speed of sound (Mach 1) for all three tuning forks. Find the average velocity.
3. Calculate a % error using the actual speed of sound at the recorded temperature. See the Handbook of Physics.
4. How does temperature affect the speed of sound in air? See the Handbook of Physics.
5. If the British Airways Concorde travels at Mach 2, how much time, in minutes, would it take to get to downtown Buffalo, 100 km west of Brockport? How long would it take you at Thruway speeds of 30 m/s?
6. When sound enters another medium, such as the wall, what remains constant?
7. If sound travels at 1500 m/s in distilled water, calculate the wavelength for each of your tuning forks in a beaker of distilled water.  

Seeing Sound Demonstration – (QuickTime movie 4.0Meg) This demonstration must be performed only by qualified personnel. For additional details, please contact Jim Keefer.

Notice how the natural gas varies in color and amplitude. As the frequency of a speaker is varied, nodes and antinodes are established along the length of the downspout. This allows for the visual measurement of the longitudinal wavelength of sound (seeing sound!).                 

Photograph and Quick Time Movie by Josh Koelle, Physics Student March 2006

My thanks to Dr. Robert Greenler (Physics Department at the University of Wisconsin-Milwaukee) for the idea of seeing sound. This demonstration was adapted from a Science Bag presentation at UW-Milwaukee.

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