Pendulums

Day 1:

Personal Experience: I haven't had a great deal of experience with pendulums, but like most people, I have been on playground swings several times in my life. I've also used yo-yos , swung on monkey bars, and been on amusement park rides like the pirate ship.

Applications to Real Life: One application that pendulums have to real life is a wrecking ball used in demolition. Also, all the personal experience I mentioned relates pendulums back to real life.

My Prediction: I think that if 2 people are on one trapeze and only 1 person is on another one, the one with 2 people will swing faster (and therefore have more swings in 10 seconds) because of the extra weight. I think that the pendulum with 2 washers will fall faster because more force is being put on the pendulum due to the extra weight.

Understanding about the Science: I don't have much understanding of the science behind pendulums. I do know that the length of the pendulum's swing will decrease each time so that the pendulum eventually slows down completely.

Predictions after 1 Washer: I predict that 2 washers will have 10 swings, 3 will have 12, and 4 will have 14. I think this because I believe that the extra weight will make the pendulum go faster. Because it's moving faster, there will be more swings within 10 seconds.

Results: 1 washer--8.18 swings; 2 washers--8 swings; 3--7.93 swings; 4--8.75 swings
This shows that the weight doesn't actually matter because the number of swings was around 8 for all the differently weighted pendulums.

Questions that I still have about pendulums:
-Why doesn't the weight make a difference?
-Does a pendulum ever completely stop?
-Does the angle at which the pendulum starts make a difference?
-Does the length of the pendulum's arm make a difference?

Analysis of questions:
 
a. My 3rd and 4th questions could be answered using the materials we have in class. We could set up the pendulum at different angles by simply measuring different angles with the piece of paper (11.25, 22.5, 45, and 90). We could use different lengths of string to investigate the 4th question.

b. I think that my first question could potentially be answered through further experimentation Really, this question requires a knowledge of equations and other scientific laws. However, I could experiment to see if objects of different masses but the same size would hit the ground at the same time. This way, I could see how mass affects an object's acceleration, which would relate back to our pendulum activity. This would show me that mass also doesn't matter in this situation, but I still wouldn't understand why. For this experiment, I would need objects that are the same exact size but different masses, such as a ping pong ball and a golf ball. Having a stop watch to time how long each item took to fall separately would make it more objective as well. A slow motion video of the two objects hitting the ground at the same time would be helpful as well because it probably wouldn't work out perfectly in a normal setting.

c. I don't think my first or second questions could be completely answered using the materials we were given because it's more a law of nature for which I need an explanation. I couldn't understand why the two objects reach the ground at the same time by experimenting, and judging whether the pendulum was truly stopped would be difficult. I'm going to do another Internet search to evaluate our explanation that mass doesn't make a difference. I could also find out the answer to my second question through an Internet search. It's important that students understand that the evaluation stage should be about true understanding rather than just knowing that the results of your experiment were correct.

d. My question about why weight doesn't make a difference is most important to me because I don't like to just accept this answer as "just the way it is." This shows just how important it is to still teach students in an inquiry based learning environment. They can't understand everything just because they see it happening in real life. They will see that mass doesn't matter when working with pendulums because that's what happened in the experiment, but they won't understand why unless the teacher explains it directly. Another question which really interests me is whether or not a pendulum ever completely stops. It appears to stop, but we mentioned in class how Galileo saw the chandelier moving in church. Because the earth never stops moving, does the pendulum really never stop moving as well? The third question which I find interesting is whether or not the angle at which the pendulum starts makes a difference. It seems like this would make a difference to me, but in class we measured

Day 2:

Question we chose:
We decided to experiment to see if the length of the pendulum's arm made a difference in the number of swings in 10 seconds.

1.) I didn't find this question particularly interesting, but we chose it because it was one most people in our group had asked. Also, we knew we could test this with the materials given to us in class.

2.) As I mentioned, I didn't find this question extremely interesting because I was pretty sure I knew the answer already. However, I knew that this wasn't a gurantee because I've found out during this semester that I have a lot of misconceptions. It's good to ask questions even if you think you know the answer. Knowing how pendulum arm length affects the number of swings would be helpful for someone trying to decide how long to make a rope swing or something similar. The number of swings is related to the width of the swing, and you wouldn't want the swing to be too long because it could run into another object.

3.) Our refined question is: How does the length of a pendulum's arm affect the number of swings it will complete in 10 seconds?

Data we found:

Quantitative Data:

4 inches
1st Trial: 14
2nd Trial: 14
3rd Trial: 13.5
4th Trial: 14

Average Swings =13.875

5 and 3/4 inches
1st Trial: 11.75
2nd Trial: 11.5
3rd Trial: 11.5
4th Trial: 11.5

Average Swings =11.5625

15 and 1/2 inches
1st Trial: 7.25
2nd Trial: 7.5
3rd Trial: 7.5
4th Trial: 7.5

Average Swings =7.4375

22 and 1/2 inches
1st Trial: 6.25
2nd Trial: 6.25
3rd Trial: 6.25
4th Trial: 6.25

Average Swings = 6.25

Qualitative Data:
The shortest string (4 in.) made the pendulum swing very quickly, and it got progressively slower up until the slowest pendulum (22 and 1/2 in.)

Claims based on the evidence:
The longer the string, the less swings the pendulum will complete in a given amount of time. This claim is based on our evidence because the shortest string had the greatest number of complete swings, and the number of swings got progressively larger as the string got longer.

Evaluation:
We did an Internet search and found that all the other sources we looked at agreed with our findings. I tried to do an Internet search to find out why exactly this is the case, and I couldn't find much of a real explanation. However, after thinking about it a little longer, I realized that the speed of the pendulum is faster if the string is shorter because speed is distance/time, and this pendulum is going a shorter distance due to its shorter string. The time stays the same, so this means that the speed increases as the length of the arm increases, resulting in more complete swings in a given amount of time.

Quiz Question:
The swinging experience would be very uneven because the 2 different strings are not the same length. The longer the string, the longer the period (meaning the longer string is going slower than the shorter string, so the swing couldn't have a smooth swinging motion).