Arc of a RipStik

Last term I tried using the downslope near the LRC to accelerate the RipStik downhill. During the run I realized that I could attempt a high speed run into the bottom of the slope, allow my speed to decay naturally upslope, swing around at arc top, and accelerate back down slope. The slope is very very gentle, allowing my speed to decay slowly. I proposed trying this in my blog at that time. Thus this term I tried what I had proposed.




I set up only an 800 cm course.



Chalk marks were at 0, 200, 400, 500, 600, 700, and 800 cm.



The run went well, but I lost track of which stopwatch time went with which distance. I believe I clicked off every chalk mark, plus one at arc top turn-around which was estimated at 750 cm.



The end of the tape was near the LRC. Previous trials this summer suggested a risk of going past 800 cm, there is an abrupt downslope into the LRC porch sidewalk.


Not exactly a smooth parabola, but far smoother than I had expected. I thought I might see a W or M shape, sinusoidal wiggles. While there is some suggestion of an M, and the curve is not symmetric, the data is not inconsistent with an underlying parabolic arc.

time (s) distance (cm) velocity (cm/s) theoretic v (cm/s) actual acceleration (cm/s²) theoretic acceleration (cm/s²)
0 0



0.84 200 238 188

1.71 400 230 163 -9 -14.4
2.41 500 143 143 -124 -14.4
3.09 600 147 123 6 -14.4
3.72 700 159 105 19 -14.4
5.51 750 28 53 -73 -14.4
7.74 700 -22 -11 -23 -14.4
9.26 600 -66 -55 -29 -14.4
11.16 500 -53 -109 7 -14.4
12.63 400 -68 -152 -10 -14.4
14.03 200 -143 -192 -53 -14.4
14.87 0 -238 -216 -113 -14.4







Average 30 3 -37 -14.4


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