Linear velocity of a RipStik

Wednesday was lab day two on this Thursday term start summer session. The 9:30 morning session opened with a review of how to structure the density laboratory report. A review was embedded in the example report of why the density being a constant for all sizes of soap yields a line on a graph of volume versus mass.


Then a slow roll into velocity while connecting the mathematics back to the day before. After this the 30 meter RipStik run. 



At the end of the morning session a deliberate misdirection was accomplished with the question, "What will happen to the purple circles if I went faster?" This focus on the data points elicited the expected response: the data points will spread apart. A student disagreed explaining that if I went faster the points would curve. No one suggested that the slope might change.

The 11:30 lab session began on the sidewalk. The operation of the stopwatches was explained without diagrams. 

A gusty crosswind prevented use of a rolling ball. The RipStik was used instead. These proved propitious as both the speed and direction was better controlled than for a rolling ball, no errant balls and miscues in timing, no slowing near the end of the run. Lines were added at 1.5, 4.5, 7.5, 10.5, and 13.5 meters. This greatly increased the number of data points.

That third decimal in the time is a new stopwatch. 

The RipStik produced very linear data. The high speed run was done on three meter intervals. The issue of whether the points move apart or closer together depends on both the speed and the distance intervals. The high speed run was too fast to time at 1.5 meter intervals, so a 3 meter interval was used. 

My self-timed high speed run was just under 3.0 m/s, but earlier runs where I focused on speed were slightly above 3.0 m/s. The Salomon Genesis GTX provide board grip like no other. Getting under 1.0 m/s is also challenging - stability issues flare below 1.0 m/s. At low speeds the uneven sidewalk surface also has a greater impact.

Only after gathering the data did the class return to A101. Coverage included how to assemble the lab report. A copy was made of a pre-existing 022 report, the screenshots were deleted, and new screenshots were added from a cell phone. Then the report was displayed on the Smartboard.


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