Pseudo Day 113 – Speed of Sound Lab

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Physics – April 29

Students were asked to investigate the speed of sound by measuring standing waves produced in PVC tubes.  I asked them to try at least 5 different frequencies using tuning forks or apps on their smartphone.  The could then graph wavelength vs 1/frequency and the slope should be the speed of sound.

Unfortunately the lab just doesn’t work very well.  The room gets very loud with sound, and higher frequencies get the students really confused about wavelengths because of the different modes.  They don’t know if their tube length is 1/2wv, 3/4 wv, etc.

I really don’t know what I will do about this next year.  Maybe I’ll just go back to “let’s try this out to confirm the speed of sound!”.  I also tried on my own to vary the water/air temperature to come up with an equation for speed of sound vs temperature.  I was using my Fluke thermocouple inside the tube which gives a good reading of the air temperature, but the data was terrible.  Cold air had the slowest speed, warm air had the fastest speed, and hot air was in between. I think the air is not reaching a stable temperature inside the tube.

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