055 Direct measurement of RipStik frictional force

Friday of week five, the wrap up of motion and dynamics. The concept was to tow the instructor on the RipStik in two directions to directly measure the force of friction.

Starting position with Josh on towing duty

There is a slight slope. Nine Newtons was seen on the downhill runs.

13 to 15 Newtons on the uphill runs.

Six yarn strands were sufficient.

Tow underway. Based on a 9 to 13 range, the frictional force was estimated to be around 11 Newtons. 

On Monday the downslope force was measured at 43 Newtons. The change in momentum with respect to time was 14 Newtons. 43 minus 43 minus 11 lost to friction is 32 Newtons of effective downslope force. 14 Newtons showed up as the change in momentum with respect to time. That leaves 18 N unaccounted for. The theoretic downslope force is only 19.74 N based on F=mg sin(θ). The 43  measured Newtons remains unexplained. 19 minus 11 is 12 N, very close to the 14 obtained. Better measurements of the downslope force might be beneficial to this chain of demonstrations. 

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