A Swinging Pendulum

Setting the basis for the work:

I chose to do an experiment based on the question of: what type of pendulum takes longer to come to a state of rest, a light or heavy one? I started out holding a string with a washer on it and counting one-one thousand. That was a fool-hardy idea. After a while I found my cell phone had a stopwatch option and I used some old yearbooks, the string and washers from our Laureate kit, plus a medium-small washer I already had (any washers graduating in size and weight should work), and an old broken children’s sunglasses arm to string the string through and hold it out at a couple of centimeters from the books and side of the table. I tried to tie a knot on the washer side which balanced the weight as best as I could, and I measured the string out 12 inches from the washer to the sunglasses arm. Holding the string level with the books with my hand above the washer, and using my other hand to tap the stopwatch button, I took time measurements for each washer at least three times.
The issue of what exactly constitutes rest was major because the washer never did come to a full rest. Each time it would just keep going, moving from a side to side motion into a more circular motion. Sometimes the wind would blow through the window, or a person would walk by and these motions would cause the washer to alter course. That being said, I carefully watched the washer for indications that the motion was no longer side to side and then I stopped the stopwatch. I also used the smallest washer as an anchor to rest all other washers on, so it was included into each and every experiment. With that in mind, my final calculations reached averages of small, 2.40.77; medium-small & small, 3.21.64; medium-large & small, 3.54.90; and large & small, 6.26.85. Thus, without any doubt, it is clear that the weight of the washer did indeed impact how long it took before the pendulum came to a rest. I did actually expect this to be the case, but the experiment confirmed it.

What went well during the experiment? What did not work well?

The idea of stopping the stopwatch when the pendulum was not REALLY at rest bothered me. I should like to have a better measurement than the human eye guessing at when to stop!
Also, the whole reason behind the sunglasses arm was because the string was rubbing up against the books and friction was stopping the swinging motion on one side. At other times when first starting a measurement, the pendulum would also hit the table, or books and thus that messed up the measurement as well. So, the arm was my solution, but even then there was room for the string to slide around a little bit and I would have preferred for that to not be the case.

Based on your past experiences with scientific inquiry, what modifications would you make to this experiment to get a different or modified result?

I think that another modification would be to make a hook from a paperclip and use that to hang the washer off of. Perhaps this would help keep the balance more correctly and also allow for only one washer to be measured at once. This would not change the comparison, either way, more weight would still mean more time, but it would create a more clean presentation. Yet another issue, I believe, which would improve the experiment would be to use the same washer, just adding more. The reason why I would do that is that the washers were not equally different. I had no scale to weigh them on, but some were thicker than others rather than just wider in diameter. Also, some seemed to be made out of aluminum while others out of a stronger, heavier metal. Thus, I have no real way to give you the right data to replicate this experiment, even if I were to give you diameter measurements for the washers, apart from perhaps both of us having the same Laureate Inc. Science kit.
I also noticed that the string kept oscillating. It would go in a general back and forth motion but occasionally it would move a couple of degrees one way or another. I do not have the reason for that, but perhaps the knot made is involved.

How might you set up this or a similar experiment for students in your classroom? How could you make this experiment more fun, interesting, or engaging for your students?

I have set up this sort of experiment for my students, only they were trying to use the force of gravity on the washers to move books off the table when the books were placed on wax paper, regular paper, no paper, and a towel. Setting up this experiment for students would not be hard, but getting them to identify the concerns that I listed above would take training. Only a trained eye, or at least an observant eye would notice that the string is rubbing against the books and altering the experiment. As far as more fun or interesting, I really do not know at the moment. I will have to really think about that one for a while. It is actually pretty boring to watch a string moving back and forth and wait for it to stop moving over a length of time which is close to five minutes.

How might you design this experiment so that it is relevant to students’ lives?

Perhaps we could use swings instead and let the children be the mass in that case. I don’t know, but I believe that they would at least enjoy themselves more that way. Another aspect is to create a meaningful reason for this, or to answer the question: “So what?” Why would students want to learn this? Why is it valuable or useful to them? If I currently had an answer to that, I believe that creating a fun and interesting experiment would flow naturally. However, at the moment I do not know what environment would cause them to need to know this.


What specifically would you like students to learn from this experiment? Did you achieve this goal?

While I was creating this experiment, a child/friend of mine came by. She wanted to touch the string and I had to quickly stop her from altering my trial run. To her it is a game just to watch the pendulum swinging. She started to talk about it and she was under the impression that the weight of the washers would slow down the string rather than lengthening the time in which it moved. I believe she thought this because big things often move slower than light things when they are things like cars or trains. What I don’t think that she understood is that those things are also harder to stop because of inertia. Her parents wanted her to go take a bath so I could not include her in witnessing my experiment, but I would want her to experience this experiment just so that she saw the importance of trying things out and checking hypothesis and changing misconceptions. Yes, a heavy wagon is slower to get started, but try and take that cart down a hill and see if the wagon isn’t ready to roll you over! Students do not experience this as much today because children do not need wagons. Their parents often drive them everywhere! So, if nothing else, this experiment could be a lesson in creating, and running and experiment, and re-adjusting a hypothesis as you go. I don’t think that student have any greater a teacher than to see for themselves how their expectations did not work out like they thought. If something goes differently than expected, they do not feel corrected, or called out. It is the human aspect, the attention of a teacher or colleague that can make them feel self-conscious about being “wrong”.