Waves

An special assembly involving the then upcoming election led to the postponement of the ENSO presentations on the Friday of eighth week. As a result the ENSO presentations were delayed to Monday. This pushed the RipStik wave introduction to Wednesday.


Not having to time allowed me to focus on the run, but my run was still not as straight on the center line as I would have liked. In other words, the center line itself was a wave.


I took the median time from the three timers.


I did not initially try to work out an average wavelength based on the waves divided by the total distance. I opted to simplify to a single crest to crest wavelength. My wavelength was inconsistent in any case.


The wavelength came in around 96 cm with an amplitude of 8 cm.


To get the frequency I did have to estimate the number of waves on the paper as the median time was 1.45 seconds. Note the rain leak on the paper. I picked the only leak along that stretch of sidewalk. The images below show that I only had to move east or west to have a drier location. I went on to calculate the period and the wave velocity.


To the east relative dryness.

A short way to the west was also drier.

Thursday's speed of sound measurement laboratory was performed using the direct measurement of the delay between seeing boards clap and hearing the sound. This involves distances of at least 250 meters between the clapper and the timer.


I had wanted to test Ixora casei, ketieu, for the ability to produce sound sufficiently loud to be heard, but getting the maximum volume appeared to require smacking the sticks in front of the clapper. And that made contact hard to see. No one attempted to use the Ixora casei sticks.


On Thursday morning rain made the road wet. With the sun just rising above the ridge in the east, visibility of the clapper was difficult at best, impossible at times. And that was with sunglasses.

Anjannet and Sasha attempt to see the clapper

Without sunglasses the task was impossible. So the timing crew took to using shade to block the sun and avoid having to look into the glare.


I suggested the timers move into the shade off to the side of the road to improve clapper visibility. This was also welcomed by the timers. The timers found working in the direct morning sun on the saturating humidity blacktop to be physically uncomfortable conditions.



Farther down the road, another "shade" stop. Although the shade "stops" happened to be near 250 and 300 meters, in the afternoon I started simply converting the surveyor's wheel footage into meters at the shady locations. The point at which one is opposite shade depends on the clapper/starting location. Shade may not happen at 50 meter intervals.

Anjannet

Put the timers in the shade and then calculate the distance based on converting from the surveyor's wheel.

Desmos graph with regression done in the field

 Morning results at 28 Celsius, 363 m/s. Within 5% of the value that morning.


Board shots from the pre-lab prep in A101.


Vanessa with a stopwatch

Jeremiah on the wheel


Better visual conditions at 11:00 and not as suffocatingly humid. Actually felt nicer. Did wish for a baseball cap to visor my sunglasses and deflect sun from my pate.
Using shade to time sound arrival in more comfortable viewing locations



Afternoon values were within 1% of the 31 degree Celsius predicted speed. The key to accuracy is the taking of upwards of 25 times at each location and then using the median time. Only the median times are used in the table and graph. HyperPhysics quotes 350.31 m/s and the students obtained 353.37 m/s. The latter might be more accurate given that the temperature over the surface of the road - where the sound is propagating - is known to be higher, as high as 50 Celsius. At 50 Celsius the sound speed is up around 362 m/s.





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