Swizzle rate versus linear speed for a RipStik

"Wiggle faster!" shouted my son. "Mingo! Mingo!" called out my niece, using her own word for wiggle.
Does wiggling faster produce more speed? Although initially intuitively correct, how strong is the relationship? The more one rides, the less one is certain that the rate of wiggling - swizzling - is directly related to the linear velocity.

In three sections of MS 150 statistics I gathered statistics on the porch of the college, using pillars 9.2 meters apart and a stopwatch to gather linear speed data while counting the number of swizzles.

time (s) speed (m/s) swizzles swizzle rate (Hz)
13.22 0.7 15 1.13
5.6 1.64 12 2.14
4.45 2.07 8 1.80
14.46 0.64 11 0.76
6.3 1.46 11.5 1.83
4.16 2.21 15 3.61
12.96 0.71 13 1.00
7.26 1.27 13 1.79
7.34 1.25 15 2.04

An xy scattergraph of this data yields a moderate to strong relationship between the speed (m/s) and the swizzle rate (Hz) with a correlation coefficient of r = 0.85.


Note that strictly speaking the axes are reversed - the swizzle rate is logically the independent variable that generates the linear velocity. For purely pedagogical reasons I wanted a slope greater than one and thus chose to plot speed versus swizzle rate.

"Wiggling" faster, all other variables being equal, does produce more speed. The other key variable that is not controlled for above is the amplitude of the swizzle. Amplitude is more difficult to measure "on the fly" and would likely require using water to produce a trace which could be measured post-hoc.

I would also note that swizzle rates above two Hertz were difficult to maintain, and the one 3.61 Hz value led to my flying violently off the RipStik headlong for a pillar. I was able to regain my feet, but only barely, and only after traveling forward much farther than I had planned to do so. One student was scared by the event, but the rest were entertained. Statistics class is not necessarily the dullest of classes.

Although I have no plans to do so, one could build quite a course around a caster board. A combination physics, algebra, trigonometry, statistics, and exercise sport science course - a real blend. ESS/MS/SC Natural Philosophy of RipStik Riding.

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