The question we chose to investigate in this guided inquiry activity is “Which pendulum will come to rest more quickly—a lighter pendulum or heavier pendulum?” (Sylvan Live, 2011.) My ten year old daughter was very interested in participating in this experiment. I thought it would be a great opportunity to spend some quality time and enrich her science skills at the same time. In a guided inquiry activity the student is given the question and designs an experiment to test it (Banchi and Bell, 2008.) Rylie chose from the list of questions and we designed the initial experiment together and carried out the activity following the scientific method. Our time together was much like a 5Es lesson (Hammerman, 2006.) Rylie even used some steps of the engineering design process (TEACH Engineering, n.d.) to improve upon our initial procedure during her explorations.
Our hypothesis is the lighter pendulum will come to rest faster than a heavier pendulum because the heavier pendulum will have more momentum and will swing longer than the lighter one. The materials we used are large, medium, and small washers, small paper clip, string, and an iPod stop watch.
Our procedure is very simple. First, we placed the large washer on the string and folded the string at the halfway point. This ensures the length of the pendulum would always be roughly the same. I held the pendulum at the very end of the string at a fixed point on the counter and controlled the stopwatch. Pulling the washer to the edge of the cabinet, Rylie put the washer in motion. We measured the swing time until the pendulum came to rest. Upon carrying out the first trial we came across a few problems and, like every good engineer, my daughter came up with some ideas. We realized holding the pendulum was not working. We also pulled the pendulum back too far to finish in a reasonable amount of time. So, Rylie used a plastic pointer finger to hold the pendulum in place. She taped it to the counter and suspended the pendulum from it and we started over with a shorter period. Since it was still taking more than ten minutes to come to rest, we shortened the length of the pendulum to about one foot. This worked well so we recorded three trials. Next, we placed the other two washers on a paper clip and hung them on the pendulum and repeated our procedure for three more trials. We recorded our data in Figure 1.
Figure 1.
Number of washers | Trial 1 Time (sec) | Trial 2 Time (sec) | Trial 3 Time (sec) | Average time (sec) |
1 | 3:12.5 | 3:13.4 | 3:13.3 | 3:13.1 |
3 | 3:39.7 | 3:36.1 | 3:39.1 | 3:38.3 |
Rylie concluded our hypothesis was correct. The lighter pendulum came to rest slightly faster than the heavier one, but only by about twenty-five hundredths of a second. In her ten year old wisdom, Rylie could not be convinced there really was no difference in the times for both pendula to come to rest. We found it very difficult to judge when to stop the timer because it seemed as though the pendula would keep swinging ever so slightly in perpetual motion. It seems the mass did not affect the period as long as the height from which it was dropped and the length of the string were kept the same. Since there was no difference in the period, there was no difference in the time it took both pendula to come to rest. The momentum that was gained on each down swing was lost with each up swing. So, momentum was not really a factor at all. Carrying out this experiment helped to eliminate the misconception that momentum affects the swing time of a pendulum. It gave me more accurate knowledge of how a pendulum works by being dependent on the acceleration due to gravity and the height of the initial drop. This activity definitely exposed my weakness in understanding physics. I still can’t really understand why both pendula stopped at the same time. The main reason I am pursuing a degree in teaching science K-8 is to strengthen that weakness so I am more equipped to teach to the changing science standards for my grade.
This guided inquiry activity strengthened Rylie’s engineering and inquiry skills as it would strengthen my seventh graders’ skills. This same activity is used by the eighth grade science teachers in my building, so I would not use it with my students. I could tie in motion and Newton’s laws by exploring with my students how a centrifuge works. A centrifuge makes use of centripetal force by spinning components suspended in a solution. The test tube is positioned in the centrifuge on an angle approaching horizontal. The machine exerts centripetal force on the test tube and its components. Since the contents of the tube are floating in suspension and not attached they will experience the equal and opposite force to the one holding the tube in place. The resulting “outward tug is called a centrifugal force” but is really Newton’s third law in action (Tillery, Enger, and Ross, 2008.) Biologists use centrifuges frequently to separate cells and their components by mass. When cells are broken open and spun very fast in a centrifuge, the heavier parts are forced to the bottom of the tube, while the lighter parts stay closer to the top. The cell parts can be extracted from their respective layers and studied.
Guided inquiry experiences are a challenge in my classroom due to class size and time. I have around thirty students and only forty minutes per class. Seventh graders tend to need a lot of guidance during the inquiry process. It is nearly impossible for me to assist everyone who needs help. As a result, these activities are very stressful and always take longer than the time allotted. Students who need help become distracted and off task when I cannot assist them immediately. When all goes well, students gain valuable experience in problem solving and inquiry skills. Both of which help prepare them for the work force.
References
Banchi, H., & Bell, R. (2008). The many levels of inquiry. Science & Children, 46(2), 26–29.
Hammerman, E. (2006.) Becoming a better science teacher. [Exerpt.] Thousand Oaks, CA: Corwin Press. Retrieved March 9, 2011, from http://sylvan.live.ecollege.com/ec/courses/56611/CRS-CW-4889693/articles/Hammerman_81-87.pdf/56611/CRS-CW-4889693/articles/Hammerman_81-87.pdf
Sylvan Live. (2011.) Week 2: Focusing on the E in STEM. Retrieved March 13, 2011, from http://sylvan.live.ecollege.com/ec/crs/default.learn?CourseID=4889693
TEACH Engineering. (No date.) The engineering design process. Retrieved March 9, 2011 from http://www.teachengineering.org/engrdesignprocess.php
Tillery, B. W., Enger, E. D., & Ross, F. C. (2008). Integrated science (4th ed.). New York: McGraw-Hill, p. 46.
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