The Pendulum

The questions posed in this week’s application are all concepts my classes have studied the past few years.  Despite studying motion, mass, and friction, I’ve never incorporated the use of pendulums in my teaching.  Because of this, I began to examine the question, “which pendulum will come to rest more quickly, a lighter pendulum or heavier pendulum?” 

I incorporated the assistance of a few of students to complete the inquiry. I had students explain their hypotheses and found them to be very informative.  The students involved were average students, not the “Gifted and Talented” students.  They really accessed their prior knowledge when explaining their reasoning.  For example, sample answers were, “objects with a larger mass need more force to stop, so the lighter mass will stop first”.  Another great answer I received was, “I saw an older kid and a baby on some swings and the parent had to push the baby more because he was stopping more, so the lighter mass will come to rest quicker.  This was an excellent answer because the students related the concept to something meaningful in their own life.

            The students measured one meter of string. On one string they attached a 50g washer, and on the other they attached three 50g washers for a total of 150g.  The students attached the other ends of the string to a pole suspended 2m in the air.  The washers were pulled back to the exact distance and released simultaneously.  We observed that the one washer did come to a rest sooner than the three washers.  These results occurred in all 5 trials.  Normally, if we were not pressed for time, I would have the student record the times it took each string to stop and calculate an average time for each.  The students’ hypotheses were confirmed and then we began to generate new questions based on our observations. 

            When formulating new questions and extending the activity I really tried integrating guided and open inquiry.   When completing the original procedure I presented the question “what if one string was longer than the other”, in hopes, students would formulate their own questions.  From there they did create some new, and interesting, questions.  They included, what if we pulled them back further, what if we released them form opposite sides, and, does the height of the pole matter.  These are all questions we could further investigate.

            I’m not sure there is much I would do differently.  We could extend the activity to examine air resistance.  For the high school level, students could examine how the motion of a pendulum relates to the motion of the earth.