Guided Inquiry: Which pendulum will come to rest more quickly?

This week I investigated the question of what size pendulum will come to rest more quickly.  To perform this experiment, I collected all of the materials.  This included two different sized washers (one small and one large), string, a ruler, a desk, a timer, and a pencil.  The setup included measuring out 30 centimeters of string and tying one end onto a pencil that is taped off of the edge of a desk.  The other end of the string was tied to a paperclip that was engineered into a hook.  This initial setup made it very easy to attach the different washers without having to worry about the length of the string varying.

During the experiment, I tested each different size by timing how long the pendulum took to stop swinging.  Each time I would make the string taut and raise the washer to the edge of the desk.  I would then let the string go and start the timer to see how long it would take to stop moving.  I repeated this test with each size washer three times.  After I collected all of my data, I averaged the results to find the answer to the question of if a large or small washer would come to rest more quickly.  My results were that the smaller washer came to rest a lot faster than the larger washer.  This was my initial hypothesis based on my knowledge of momentum and that fact that the larger washer had more mass.  I know that momentum is the product of velocity and mass, so with more mass there would have to be more momentum.  My hypothesis was supported in that the smaller washer stopped swinging faster than the larger washer.

While I was conducting the experiment, everything went well and it was easy to conduct and record my results.  I initially had two different pendulums, one with the smaller washer and a different one with the larger washer.  It was very hard to make sure that the string was the same length.  That was when I decided to use one string and a paperclip to help keep that variable the same.  It was frustrating when I was trying to tie on the separate washers.  I had the same length of string measured out, but my knots were not identical.  When I revamped my initial setup, I had on problems during the experiment.  Also, I was going to use a ruler to see how high to drop the pendulum, but I decided to simplify that by going from the edge of the desk.  This was a great choice because I know that not having to measure to a certain height each time would be easier for my fourth graders. All they have to do is pull the string tight and raise it to the desk and let go.  The simpler the better.

Based on my past experience with scientific inquiry, a modification to get a different result could be to focus on the length of the string.  If I were to stay with the same size washer and just change the string length, we could investigate if the length of the string affects the amount of time that the pendulum swings.  This would be a different variable to test.  We could also keep the length and the washer the same and change the height from which we start the pendulum.  That would also produce different results.  The children would find out the at the greater the potential energy stored, the more kinetic energy will be released.  That would be a great connection between momentum and potential versus kinetic energy.

I would set this experiment up in my classroom in the exact manner that I did the experiment.  I had my students in mind when I designed the guided inquiry activity because I always like to make things relevant to the fourth graders that I teach.  I think that it would be fun to try three different washers:  small, medium and large, and collect data on all three.  I also think that it would be fun for the kids to measure the mass of the washers using a triple beam balance before they conduct the experiment.  This way they would also get practice manipulating this very important scientific tool.  After answering the initial question, it would be really neat to propose to the student the challenge of creating a pendulum that will swing the longest and having a class competition.  They love to be challenged and really like working towards a goal.  I would set it up as if they were designing a new amusement park ride and the people that were hiring them wanted to get the longest ride possible from the initial drop.  All of the students have schema related to an amusement park and this would engage them.  The only catch would be that the experiment would have to be able to be replicated numerous times in front of the class.  This would encourage them to record their data.  I plan on using this activity when we do our lesson on forces in the spring.

Specifically, I would like the students to understand that the more mass an object has the more momentum it will produce.  I would also like them to see that energy can be stored and released.  I achieved this goal through my discovery during the experiment.  I am certain that my students will see the results as well.  I especially would encourage the use of a balance to measure the mass of the washers prior to the experiment.  I know that the students can see that one has more mass, but I really would like to reinforce the use of the triple beam balance as well.  Hopefully, upon completion of this activity, the students will bring momentum to life and will be reminded of the science behind rides the next time they get on a pirate ship at an amusement park.