danaleeling

Probability as relative frequency is introduced by having students blind pull a marble from a bag with 35 blue marbles and 15 green marbles.  With 18 students in attendance the sample relative frequency/probability results were almost unnaturally close to the population probability.  This example is clear enough, but obtaining relative frequency based probabilities from ratio level data could use a good example. Both the car speeds and height data are rather clearly interval level data - no fractional data exists in the data set. Perhaps marble masses? Of the 18 marbles? That would be ratio level. That would lead to a four class histogram which could then be used to discuss the way the class upper limit is handles in ratio level data.

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 ...

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...