John P. Crotty
We tried an experiment on our first Friday to see if we could measure how far a bicycle could travel in different gear combinations. We will talk about it next, but first let’s look at what they’re talking about in a gear table that you find in the rear of many bicycle books. When a book talks about how many inches any particular gear is, the inches refer to the size wheel any particular gear would require if it were straight drive. Many of the old high-wheelers had a fifty-four inch gear. That means that the diameter of the front wheel was fifty-four inches. This made the bike cumbersome and unsafe. How would you find a fifty-four inch gear on my bike? The formula is the product of the number of teeth on the front sprocket divided by the number of teeth on the rear sprocket times twenty-seven inches, where twenty-seven inches is the wheel diameter. So, on my bike with fifty teeth on the front sprocket, I would have twenty-five teeth on my rear sprocket to attain a fifty-four inch gear. This formula is a perfect spreadsheet application. We will be able to generate the table. My kids get excited when they do real work.
Now, let’s look back to our first experiment. It was a horror show. This was our first time breaking the traditional classroom setting. We worked in the courtyard outside of the school. The courtyard has cement blocks six feet square. The skepticism of my immediate boss and the principal did not help. They could not understand how being outside with bicycles was related to computers. So the first problem was to assure my students that it was ok to have fun while learning.
We had three bicycles. I had brought in mine, which all the kids laughed at just because it’s older than they are, and two students had brought in their bicycles. We only had one tape and it was twelve feet, but we had three yard sticks. We marked off a starting point and then marked off every six feet so that the students would have a line to measure from. I should have marked off every three feet since they were unable to measure backwards.
We broke the class into groups. We had riders, recorders, judges and measurers. We assigned people to their groups after we got outside. I should have done that inside. The courtyard in some places is only twelve feet wide so we only used two bicycles. Mine has stirrups which the rider did not know how to use, so after he smashed one by driving it into the ground, we retired my bike.
For the experiment we asked the rider to pedal two complete revolutions. Because we had not gone over anything beforehand, the riders were trying to stop after two revolutions. This caused them to coast. Our other difficulty was the slippage in the crank. I had wanted two revolutions to minimize initial resistance, but the one bicycle crank seemed to move twenty degrees before the bicycle started to move. The other difficulty was in trying to judge the point where the second revolution ended. In this class two of my students are mothers. They finally became frustrated, took control, and started collecting data. We then told the rider to continue to pedal smoothly and the girls were able to get readings.
At the end of the experiment, we asked the two riders to go all out over the entire course which was about four hundred feet long and the riders were winded. They felt that that distance should be long enough for future experiments where we will time the riders at fixed intervals in different gear combinations.
