Measuring the speed of sound

The class again used the approach of measuring the time delay for a clap from distances out beyond 200 meters. That one can hear the clap of two boards from up to 558 meters away, with the wind working against us today, remains amazing to me. While the 8:00 class would be eight percent low (which would have been good in the days of echo-synch clapping), the 11:00 class would measure a speed of 351 meters per second, only 0.3% high. Within a third of a percent of the speed of sound.

This term the new El Niño presentations extended into Monday. Although the presentations ended by 12:40, the remaining 20 minutes was insufficient to introduce waves. This pushed the RipStik run back to Wednesday.

This term I opted for three sheets of poster pad paper for a total length of 248 centimeters. There were 3.75 wavelengths on the sheets, suboptimal but achieving an integer number of wavelengths is nigh on impossible.

Although I strove for a straight centerline, the centerline still curved. This is tough, maybe tougher over 248 cm (two sheets are 165 cm). Despite the challenge, I felt the three sheet run worked better overall for displaying the overall wave nature of the line.

This term the extra space afforded me the ability to remain in the field and do all of the work in the field. I opted to show both the time and space equations, introducing the idea that some systems are governed by multiple equations. Maxwell's equations, the equations of general relativity.

On Thursday the distances looked long, but the claps could be heard distinctly out around 200 meters. Rain stymied launch at 8:00. Eventually the students suggested an admin to dining hall distance, which I knew to be too short. That thought, however, made me realize one might be able to time a clap from north faculty to the rear of the dining hall or the women's residence hall. Both were tried with limited success. There is no beating the road for sheer distance and ability to carry the clapping sound.

Renster, Marcyliza, Petery, Regina, Marsha, Macy, and Mary-Ann out beyond 200 meters

Sharisey, Marcylize, Renster

Headed west under suboptimal conditions. At the rise in the distance are the clappers. 

This term I asked for student volunteer with a cell phone to share their number with me. This proved invaluable. When Ioakim chose to use a "double pump" the first pump caused the timers to false start. I sent text messages to try to correct the problem, but to no avail. Then a student said, "Why not call her?" After I smacked my own head for not having thought of that (who knew you could make voice calls with these computers called cell phones?), I called and sorted out the double pump issue. 

Out near 400 meters

The group came back together to share data

The afternoon saw more rain than the morning class. Again having a cell number proved useful: I was able to call the clapping team and tell them to take shelter. When the rain stopped, I called them to return to the road. The rain was heavier at the clappers end of the road unfortunately, and that team was rather thoroughly wet. 

Waiting for the rain to pass.

Data from the two sections and the combined data, raw data on the right. The median was used to reduce the impact of timing outliers.

The loss of Monday to El Niño presentations meant that the demonstration of the chain wave never happened. The Friday wave quiz showed even weaker than the usual weak performance on a graphical analysis of a wave, so on the next Monday I went to do the chain demonstration. Only no chain. So I used a rope and a longer table set-up to demonstrate waves on a rope.


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