Physics Core/AP 1 and 2

Speed of Sound

Speed of Sound

Goal: Measure the Speed of Sound (oscillation method)

The speed of sound waves depends on the wavelength and frequency of the wave. If the frequency is known, and the wavelength can be measured, then the speed of sound can be determined from the relationship c = λ * ν.

In this experiment, a sound wave travels from the tuning fork to the end of the tube and back. The wave is inverted if the end is closed, and simply reflected if the end is open. The first harmonic gives the wavelength from the length of the tube where it occurs.

 Closed-Open Tube Open-Open Tube

This lab is based on Ayman Badra's laboratory Measuring the Speed of Sound in Air using a Resonance Tubefrom the PHYSICS 1030L course at the University of Tennessee, and on the Lake Oswega school district Resonance and Speed of Sound Lab. You should review these lab descriptions to understand the modifications and sources of error possible in the revised setup described below.

Materials
• Tuning fork(s) and mallet (a wooden or rubber kitchen spoon will work)
• Two sections of tubing, one of which can fit inside the other. Tubing can be made of PVC pipe, cardboard, or soda can bottles. It needs only to contain the air and provide a resonance chamber. A very stiff, narrow mailing tube with a closed end works well for the outer tube.
• Thermometer
Procedure
1. Identify and record the frequency of the tuning fork.
2. Record the current air temperature.
3. Open-Open Tube Run:
• Position one tube inside the other.
• Strike the tuning fork and hold it in front of the open end of the tubes.
• Pull the inner tube out to lengthen the overall tube structure. Listen for resonance (sudden sharp increase in volume).
• Record to overall length of the tubes in meters.
4. Closed-Open Tube Run:
• Seal off one end of the outer tube with a lid, stiff paper, or set the outer tube firmly on a hard surface.
• Repeat your procedure above to determine the shortest resonance frequency for the closed-open tube.
• If you have other tuning forks, use them in separate runs for both the open-open and closed-open tube scenarios. Record the tuning fork frequency and tube length at maximum amplitude.
Data Handling
1. Create a table for your data. Include temperature, tuning fork frequency, and length of tube at maximum amplitude for each run.
2. Calculate the wavelength appropriately for the tube setup (open-open, closed-open).
3. Calculate the speed of sound from the relationship c = λ * ν.
4. Determine the theoretical speed of sound in air at your recorded temperature, based on your textbook discussion.