045 Replication of conservation of energy with a RipStik

This term a Thursday holiday turned the banana leaf marble ramp laboratory into a Wednesday demonstration using a Hot Wheels car and track. Rather than do the smorgasbord of equations approach of spring 2025, Friday was used to replicate the Wednesday demonstration but used the RipStik on the sloped sidewalk.


Three heights were set up with vertical drops of 11 cm, 28 cm, and 37 cm.


Eleven centimeters was on the pillar base.

Twenty-eight centimeters was at the bottom of the post. The nuts actually proved useful in tensioning the line.

Thirty-seven centimeters was on top of flanges. This measurement has come in at higher values in the past. Fall 2024 the height from 21 meters was measured as being 0.7 meters or 70 centimeters. 

The first double set corresponded to the 11 centimeter drop.

Twenty-eight cm

Lines hooked on a nut to clear the sidewalk. Based on an image from fall 2024, the launch this fall was from the 21 meter mark.

As noted above, I think this corresponds to 21 meters uphill, but no measurement was made of the slope.

The sidewalk became the whiteboard. Those are the theoretically predicted velocities based on v = 35.67√h from the Wednesday demonstration laboratory. The heuoate inscribed in chalk on the post above.

These values were on the post prior to the RipStik runs.

After each run the actual velocity was written in blue chalk. Note that the 180 cm refers to the speed trap distance which was kept identical to the one used for the Hot Wheels car on Wednesday.


Results were also posted on the post. If the 21 meter posts are 70 centimeters above the bottom of the slope, then the predicted velocity is 298 cm/s, sufficiently above 270 cm/s measured as to account for frictional forces. Was the yarn truly level? All indications are that the yarn lines were not truly level.


Blue data pints were the predicted values based on 36.67 √cm/s. Due to rounding the field value best fit was 35.60  √cm/s. The orange data points were the actual results, unexpectedly faster than predicted. Which suggests that the height measurements were systematically low.

The best fit saw a k of 45.4 √cm/s, exceeding the predicted maximum value of 44.27 √cm/s. In theory k is √2g. Historically k has come in under 44.27, often significantly under. Coming in over 44.27 is puzzling. The shape of the curve supports the square root model, only the matter of k is left yo be resolved. Science works like this: theories are tested, and results can be a mix of confirmations and disagreements. Here the mathematical model is confirmed, the explanation for k is unresolved but appears to be a result of underestimating all the heights. 

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