# Speed of Sound

1. Feb 15, 2010

### demode

I just completed a lab in which we created standing waves in a fixed length of pipe using a function generator. An oscilloscope was used to measure the amplitude of the waves. The frequency was changed until a resonant condition was met, and then the location of all the nodes/antinodes was measured. We used the distance from antinode to antinode to measure the wavelength of the wave. (One wavelength = 2X the distance measured). This was repeated for two additional frequencies.

Once we had this information, we calculated the velocity of the waves using the equation:
v = frequency * wavelength.

These values were then compared to the "actual" speed of sound, as calculated from the equation v = 331.5 +.607(T), where T was 24 Celsius.

So here's my question: The calculated velocity of the first standing wave was smaller than the "actual" velocity. The calculated velocity of the second and third standing waves was BIGGER than the "actual" velocity. What explains this? Can the difference be attributed to human error in measuring the distance between antinodes or is there some physical phenomenon going on?

2. Feb 15, 2010

### Doug Huffman

The first error source I would suspect is your "equation" model. I see, for instance, no consideration of the stiffness of the pipe. I see no mention of the size of the error or the measuring protocol. Was the error consistent across the many students' project?

As I recall my freshman physics class, the bulk of the lab lecture was on evaluating the errors.

3. Feb 15, 2010