RipStik Waveform

I again used a three poster pad sheet run to record the wave on, again using the sidewalk in front of the south faculty building. I did shift to using three stopwatches and had the students time the run. Two of three stopwatches obtained data, the third was in countdown mode.

I made four marks at 25 cm from the south edge of the paper. I intended for these marks to try to keep me on a straight line. Despite these marks, the apparent centerline wobbled. That said, the marks were still helpful.

This demonstration was equipment heavy. The trade winds were strong today, and I had to use wide masking tape to hold the paper down. The three sheets were held together using Scotch tape, the edges with the wide masking tape. I also pre-swept the area with the broom. Other equipment included the aforementioned three stop watches, a calculator, and the new fiber glass tape rule. Things I forgot initially were scissors, my clipboard, a meter stick for the centerline marking, and markers.

The wave was not unreasonably curved, but perhaps also not reasonably straight. The amplitude on the two waves differs markedly, evidence that I swizzle one foot more than the other.

The sidewalk is suboptimal for student note taking purposes. The sidewalk, however, is a better forum for holding attention than the classroom.

Four wavelengths were laid down across 250 cm. That put the wavelength 𝜆 at 62.5 cm. The amplitude A was 7.0 centimeters. The amplitude is the distance from the centerline to the top of a crest or from the centerline to the bottom of a trough.

I swizzled ("wiggled") four times in 1.65 seconds. Each "wiggle" took 1.65 seconds ÷ 4 waves =  0.4125 seconds. The duration of time for one wave is called the "period." Physics uses a capital T for period. Unfortunately that gets confused with the T for temperature in a course like physical science. I sometimes use a variation on a Greek "tau" 𝜏 for period to reduce some of the confusion.

The "beats per second" is the frequency f. The frequency f was 4  waves ÷ 1.65 seconds = 2.42 cycles per second or 2.42 Hertz. The speed at which the waveform moves ("propagates") is 𝜆 × f = 62.5 cm × 2.42 cycles per second = 151.5 cm/s

The wave form as rendered by WolframAlpha.


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