Exploring Standing Wave Velocity: Human Error or Physics?

[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?

 

[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.

 

[Dadface]

All experiments are subject to systematic and random errors.When using your results to calculate the speed you should,ideally,have estimated the percentage error and expressed the results accordingly eg speed of sound=330m/s+or-5%.Even what you called the "actual velocity" cannot be measured to absolute accuracy and precision.Taking errors into account there should be overlap between the "actual velocity" and the calculated velocity.

 

[Dadface]

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.

I suspect also that something like lycopodium powder was used and if so the would be large errors in measuring the internodal distances.

 

[PJC01]

I would first like to commend you on your thorough understanding and execution of the lab experiment. It is important to carefully measure and record all data in order to accurately analyze the results.

In this case, the discrepancy between the calculated velocity and the "actual" velocity can be attributed to a combination of human error and physical phenomenon. Let's first consider the possibility of human error in measuring the distance between antinodes. It is possible that some measurements were slightly off, leading to a slight difference in the calculated wavelength and ultimately the velocity. Additionally, small variations in the frequency and amplitude of the waves could also contribute to the discrepancy.

However, there are also physical factors at play that can affect the velocity of standing waves. One possible explanation is the influence of temperature on the speed of sound. The equation you used to calculate the "actual" speed of sound takes into account the temperature, but it is based on a standard value of 24 degrees Celsius. If the actual temperature in the lab was different, it could lead to a difference in the calculated velocity.

Another factor to consider is the properties of the pipe itself. The material, shape, and even imperfections in the pipe can affect the speed of sound and therefore the velocity of the standing waves. These physical factors can also contribute to the differences between the calculated and "actual" velocities.

In conclusion, it is likely that both human error and physical phenomenon played a role in the discrepancies between the calculated and "actual" velocities in your experiment. As a scientist, it is important to carefully consider all possible factors and sources of error in order to accurately interpret the results of an experiment.