RipStik waves, Android sound apps, and the speed of sound

I started the class on Monday on the sidewalk with a RipStik laying down a wave.

This term I opted to lay down four sheets of paper which produced roughly three waves in 2.29 seconds across a distance of roughly 334 cm. Actual measurements of the wave came up with roughly a 120 cm midpaper wavelength and an amplitude of about 9 cm, a good amplitude from a historical perspective. The wind was negligible, so only the ends were taped down. A tape rule was used in lieu of a meter stick, although a yard stick was on hand to help with the centerline.

On Wednesday I used a rope to again demonstrate wavelength, amplitude, period, and frequency. Then I used a bouncing golf ball to demonstrate frequency and period. I leverage this to show the linkage to sound with meter stick bouncing on the edge of the table. And then I used Android apps running on a ChromeBook and the large screen television to display waveforms for sound. Which led to "seeing" the frequency of sound as waves and that segues nicely into the speed of sound.

An oscilloscope app running on the laptop and large screen. I used the same apps on the smartphone to generate tones displayed by the oscilloscope.

The  rope rig was new this year, this worked surprisingly well.

Board notes.

Thursday the class set out to measure the speed of sound. I knew from past experience that I needed a solution to the traffic issue especially at 8:00. The removal of the bulldozer from the north side of the road and the clearing of that side caused me to realize that a new option might be possible. I moved the zero point almost 100 meters west, to just west of one of the eastern half moon junction.

A triangular rock marked the zero point.

The eastern junction.

The skies were overcast to broken, humid but without sun and, for the first time this week, no rain.

In the morning class Heather had the surveyors wheel. Tulpe would remain with Rayden with Tulpe's cell phone as the means of communication.

Another change this term was to do fewer timings at more measurement locations. I rejiggered the distances conversion sheet to run every 25 meters from 200 meters to 550 meters. My goal was seven or nine times at each stop, but even numbers occurred and some stops had twelve times. I wanted to make finding medians easier while making the graph more densely populated.

Cars were still an issue, but less so than I expected. Rayden was well visible when at the north side of the road, especially if we timed from the southern side. Morning glare was not an issue this term due to the overcast skies. I had a hat and sunglasses anyway.

Data gathered in the field with the conversion sheet in the back. Fewer times per distance, more distances.

Benter, Juntwo, Gregorlyn, Myra, Theana timing. Suzanne behind Theana.

Final distances were large, here near 500 meters.

Rayden clapping. Surprisingly one can still see Rayden clapping at this range. Human eyes are good.

525 meters and the sound was louder: down here there is no traffic and the vegetation forms a sound tunnel. Hearing was easy. Seeing was challenging.

Pohnpei black pepper. Strong.

In the afternoon Flora took charge of the surveyor's wheel.

Timing was done by Saileen, Yummy Crystal, and Arleen among others. The 11:00 class made it out to a record 550 meters.

The new lounge area in the dining hall was near on the perfect place to work on medians.

The median finding work was split up. A later re-analysis of all of the data is contained in a spreadsheet.


8:00 section data to 525 meters.

11:00 section data to 550 meters. Note 450 meters had been omitted when I entered the table on my smartphone.

A look at both data sets.


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