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055 Force of friction for a RipStik

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The gist of this demonstration is captured in the following image. The RipStik is towed at a constant velocity and the force required to maintain that constant velocity is read off of the spring scale. As long as the velocity is constant, the change in the momentum is zero, and any force is due almost entirely to friction. Air resistance is not a factor. There are frictional forces with respect to the floor and within the bearing assemblies of the RipStik. Prior to this Friday demonstration the RipStik bearings were dowsed in WD40. Although a red 20 Newton spring scale was used a year ago , the white 30 Newton spring is easier to read. The class was done as another cold open. No roll call up front. No going into the classroom. I arrived at 12:00 and asked Leona to tow me westbound on the sidewalk. I called back to the few who were there on time to come and read the spring scale. I explained that this was just like the laboratory done the day before, but now the ...
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Force of kinetic friction

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This term there was no cold open with students trickling in one by one. Enough students arrived on time to roll directly into the laboratory. This term printing the grit conversion sheet was forgotten. Upon returning to the faculty building, the power went off, taking down the printer. A return to the prep room turned up a grit conversion sheet in the cabinet. Only one pair would work on grit versus the force of friction. This term the weight bucket was not forgotten, but the weights continue to evaporate. Eschewing a detail description on the board, the laboratory opened with a single line on the board, What factors contribute to the force of friction? Weight? Surface roughness?  Then a silent demonstration was done using a limited number of weights. Slot weights are evaporating. Options need to be explored. Stackable slot weights do seem to be  ideal. Leona and Jemira were the group working on grit size versus the force of friction. They w...
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Ethnobotany at Pwunso: Gymnosperms, spice trees, timber

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Bus arrival at Pwunso was 15:54. This would impact the end time. The class began at the Ficus prolixa and by 16:03 was headed to the Syzygium aromaticum. From there the usual circuit was followed: Araucaria columnaris, Cinnamomum verum, Cycas, Piper nigrum, Coffea robusta (the last having fallen over recently), and Myristica fragrans (16:16). Myristica fragrans is still the time consuming stop and the class headed to the Eucalyptus deglupta at a late16:28. Eucalyptud deglupta  Having seen high school students come up the road from the back gate, I jogged ahead to see if the back gate might be open. The gate was not, which cost time. Perhaps there is a gap in the fence line. Unlikely that the students hopped the fence - some were wearing school skirts. Perhaps the gate was locked after the school commute.  Shirleven, Carmegarose, Geneva 16:31 reversing course to go around to the tennis courts. Anastasia, Ne...
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Botany laboratory five: Pwunso

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An early arrival permitted a scan of what to see and what to skip.  Averrhoa carambola This term the mid-garden was skipped as there were no fruit either on the Averrhoa bilimbi or the Garcinia xanthochymus. On time arrivals awaiting the bus at 11:34 including Sweethy, Susan, and Mirabella. Santriko and Harston. The bus didn't roll out from the LRC until 11:15, arriving at 11:35. The morning had been rainy, with a shower at 10:45, but for the rest of the field walk the rain held off. Cassia fistula in bloom  The field walk began at the Ficus prolixa. This was a dual coverage walk for the five students in botanyj and ethnobotany. A sixth ethnobotany only student joined the botany section walk.  Amaryssa, Lensilee , Beverly, and Lyviane Susan and Harston  Alex Geminaro Cinnamomum verum  After a visit to the western end of the garden, the class vi...
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