Force of friction on a RipStik

A summer session Friday provided an opportunity to pull together a loose end and to introduce the summer solstice.
The measurement of friction was tackled differently than in prior terms. Instead of directly measuring the force of friction using a spring scale tow line, a calculation was made based on the loss of momentum. The loss was calculated between two non-zero velocities, a new approach. No zero momentum.


The board was brought across a 1.5 meter speed trap,  allowed to coast for 4.5 meters, and then the velocity was measured again in a second 1.5 meter speed trap. 

The second speed trap

Runs were started from the LRC with speeds targeting a midrange velocity of 1.4 to 2.2 m/s. This kept the roll out above 1.02 m/s. Velocity losses were 0.40, 0.27, and 0.45 m/s.


Measurements were laid out ahead of class.

Mass with the RipStik was also measured in advance and  a spreadsheet was prepared.


Data from the in-class run, initial velocity.

Final velocity. Time from the Xinko PS-1000 stopwatch which includes a third decimal place.

Calculation of the force via the change in momentum over the time from 1.5 meters to 6.0 meters.  A force of -16 Newtons which agrees surprisingly well with a  -11 Newton force measured by spring scale spring 2025.

The approach used this summer better pulls together the threads of force and momentum than a direct measurement.




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