6661 Pendulum Experiment- Guided Inquiry

In this week’s experiment I chose to investigate the following question:

Which pendulum will come to rest more quickly—a lighter pendulum or heavier pendulum?

I began by gathering my materials: steel, washers, nylon string, tape, measuring tape, and stopwatch. I affixed the string to the 1 ½” steel washer, then from the knot on the washer I measured 12” of string and I placed a piece of tape to mark the measurement. Next, I placed another piece of tape on top of the first piece and attached it to the edge of the table. (see Figure 1)

Figure 1.


Finally, I was ready to being my experiment. I knew I had to hold the pendulum with one hand at ninety degrees and start the stopwatch with the other hand. I pulled the pendulum up next to the edge of the table with the string stretched out firmly; I released and started the stopwatch. But was it exactly at the same time? This is when my human error was going to haunt me forever. In addition, I realized the starting point of the pendulum was marked, but how could I ensure that the string had the same tension in every trial? I never realized that the 1 ½” pendulum would take an average of 18 minutes and 36 seconds for it to stop. Whereas the ½” pendulum took an average of 6 minutes and 54 seconds. (See table 1 and 2) I was frustrated when all the trials took a different amount of time. None of the six trials for each washer were consistent. I knew that the bigger washer would take more time because of the air resistance the smaller washer took the least. I had the answer to my question, but that was not enough. When I experimented using an interactive pendulum the results was exact (Dubson & Loeblein, 2009). Every action did have an equal and opposite reaction; every swing to the left equaled every swing to the right (Tillery, Enger, & Ross, 2008). I was able to control all the variables to the decimal including the angle and the tension on the string. The stopwatch function was helpful because in the simulation I was able to pause as if I have an extra set of hands.
When I set up this experiment in my classroom I will first allow them to explore the interactive pendulum before they make their own, that way they would know all the factors that may change their results. I would ask them to research clocks and how a pendulum plays an important part in them. In addition, I would also introduce my students to Newton’s Cradle.

Overall, I would like my students to learn that there are many forces that effect momentum, and that it is not the mass of the washer that stops the smaller washer. As Galileo noted in his theory of falling object, it is the air resistance that slows down the smaller object(Tillery, Enger, & Ross, 2008). In addition, I would like my students remember that we used STEM and the 5E's to solve the problem.

References:

Dubson, M. & Loeblein, T. (2009). Interactive Simulations: Pendulum Lab. Retrieved
May 12, 2010 from http://phet.colorado.edu/simulations/sims.php?sim=Pendulum_Lab

Tillery, B. W., Enger, E. D., & Ross, F. C. (2008). Integrated science (4th ed.). New
York: McGraw-Hill.

Table 1

1 ½” STEEL WASHER PENDULUM

Trial Amount of time
to stop

1st trial 16 min. 50 sec.

2nd trial 20 min. 5 sec.

3rd trial 18 min. 53 sec.

Average 18 min. 36 sec.



Table 2

½” STEEL WASHER PENDULUM

Trial Amount of time to stop

1st trial 7min. 15 sec.

2nd trial 6min. 20 sec.

3rd trial 6 min. 24 sec.

Average 6min. 54 sec.