If only one student is timing the trials and that person is a little quick to stop the time on the last few trials, the graph of diameter versus time to deflate may appear linear. Thus, your students should establish definite procedures for performing the experiment. As shown in the video, it may be helpful to stop after each group has done one trial and re-emphasize or modify procedures. One person measures and one person verifies the balloon's circumference. If calipers are available, they can be used to measure the diameters.
Several students use stopwatches to time each trial, and the times are averaged.
It should be noted that there are advantages to having each group of students determine their own procedures and create a spreadsheet based solely on their own data. Ideally, the experiment could then be repeated with any changes in procedure determined by the students. This lesson guide is meant to provide tips for producing a data set that closely reflects reality so that the emphasis of the lesson can be on the intended objectives related to functions and slope. Resources When entering the data in the Class Data Sheet, use the mean of the values obtained by all the groups in the columns measured diameter and time to deflate. This technique will increase the likelihood of graphs that display or strongly suggest the actual relationships between the given variables.