Investigating Sound: Using Open Tubes To Demonstrate Beat Notes
In this interactive demonstration, students will observe while the teacher creates two sound frequencies using open tube resonators of nearly identical length. The nearness in length produces two slightly different frequencies which interfere with each other to produce a beat note
Beat notes are used by musicians to tune instruments. Frequencies that differ by less than 7 Hz can be detected by the human ear. The frequency of the beat note is equal to the difference between the frequencies of the two sound waves.
2. The students will observe the generation of sound using an open tube resonator.
3. Upon determining the frequency of the sounds produced, the students will calculate the beat frequency.
1. Production of sound in open-tube resonators.
2. Production of beat notes by instruments slightly "out of tune".
Context for Use
Resource Type: Activities:Classroom Activity:Short Activity:Demonstration, Activities:Lab Activity
Grade Level: Middle (6-8), High School (9-12)
Description and Teaching Materials
The materials for this demonstration are: two metal tubes, two Bunsen burners, and heat resistant gloves.
Students are to quietly listen to the two separate sounds produced by the individual tubes and then listen to the sound produced when both tubes produce sound at the same time. With older students and with available electronic equipment, the demonstration can be extended into the measurement of the two sound frequencies and the mathematical calculation of the beat frequency. Older students might be allowed to perform the activity themselves with proper safety precautions and supervision.
For closure, music students will be asked to report back to class any experiences in the coming days of out-of-tune instances. Review of interference of sound waves using the marker board would also be beneficial.
This activity is an adaptation of Singing Tubes as produced by Flinn Scientific Inc, Batavia Illinois. Physical Science FAX, Publication No. 6305
Teaching Notes and Tips
6.II.C.6 Waves move at different speeds