Phy 231
Your 'pearl pendulum' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** Your general comment, if any: **
** Your description of the rhythm of the pendulum when tilted 'back' **
When I tilted the bracket back a little bit, the pearl’s rhythm increased a lot. The pearl’s swing was very small; the pearl did not go far away from the bracket after it was released. The farther I tilted the bracket back, the louder and harder the pearl hit the bracket.
** Your description of the rhythm of the pendulum when tilted 'forward' **
I believe the rhythm was constant. If the rhythm does change, it was too small for me to hear. The string came closer and closer to the bracket but the pearl also had less and less momentum. I believe these two things canceled each other out so the rhythm was constant.
** Your description of the process used to keep the rhythm steady and the results you observed: **
I started by putting paper under the bracket but it wasn't enough, so I folded two dollar bills in half and put it under one side of the bracket. The rhythm became steady and hit the bracket 22 times.
** Your description of what happened on the tilted surface (textbook and domino), rotating the system 45 degrees at a time: **
constant, increasing, constant, constant
I put one domino on the top right corner of my textbook and another on the bottom left of the text book. The first data obtained is when the bracket was parralel to one of the sides of the book. The next data was collected when the book was facing the binder, the next parallel to one side of the book, and the next facing the side of the book without the binder.
** Your description of how you oriented the bracket on the tilted surface to obtain a steady rhythm: **
I would have the pendulum parallel to a side of the book. Facing either the top of the book or the bottom, it doesn't matter.
** Your report of 8 time intervals between release and the second 'hit': **
.525
.469
.484
.453
.547
.500
.594
.594
I put the pendulum parallel to a side of the textbook, released the pendulum as I released the time button on the TIMER program and pressed the timer the second time the pearl hit the bracket.
** Your report of 4 trials timing alternate hits starting with the second 'hit': **
.531, .563, .563, .531
.500, .561, .545, .549
.434, .563, .438, .578
.469, .578, .484, .594
.484, .532, .532, .532
.532, .516, .547, .532
.434, .578, .609, .422
.563, .516, .547, .531
I released the pendulum at the same time I released the time button and every 2nd time the pearl hit the bracket, I clicked the time button. These are the times of two full swings of the pendulum.
Between 'hits' the pendulum undergoes half of the full swing.
** The length of your pendulum in cm (you might have reported length in mm; the request in your instructions might have been ambiguous): **
8.7 cm
** Your time intervals for alternate 'hits', starting from release until the pendulum stops swinging: **
49, .55, .53
** Your description of the pendulum's motion from release to the 2d hit: **
The pendulum is released from extreme point and then strikes the bracket at equilibrium.
That's where the interval starts and stops, but what happens in between? We are talking about the second 'hit', and you haven't mentioned the first 'hit' or the nature of the motion between.
** Your description of the pendulum's motion from the 2d hit to 4th hit: **
The pendulum between first hit and second hit starts at equilibrium, goes to extreme point and then back to equilibrium. The difference between first hit to second hit and release and first hit is the difference in starting position. First to second starts at equilibrium, release to first starts at extreme point.
Good description of the difference. You need more description of what happens in between so that you can understand why there should be a difference in the time intervals.
** Your description of the difference in the pendulum's motion from release to the 2d 'hit', compared to the motion from the 2d 'hit' to the 4th hit: **
The motion between release and second hit is shorter in length than from the second to fourth hit. From release to second the pendulum is going 270 degrees and from the second to fourth hits, it is going 360 degrees. Between release and second hit, it takes less time.
OK, this time you did correctly specify the difference. This should lead to the correct expected ratio of times.
What should be the ratio?
** Your description of the difference in the pendulum's motion from the 2d to the 4th 'hit' compared to the motion from the 4th to 6th hit: **
According to my results, the difference is minimal. They are almost identical in time of run. But between the fourth and sixth hit, the pendulum travels less distance but has less momentum.
** Your conjecture as to why a clear difference occurs in some intervals vs. others: **
The first time interval is only traveling 270 degrees rather than the usual 360 degrees as the other time intervals.
** What evidence is there that subsequent intervals increase, decrease or remain the same: **
I would expect them to decrease but the rhythm remains constant for a while. It would be slow to decrease. For me, the pendulum would hit the bracket around 20 times every time I released it.
** What evidence is there that the time between 'hits' is independent of the amplitude of the swing? **
I would say this experiment supports the hypothesis because the rhythm remained fairly constant even when the pendulum was on its tenth or eleventh hit. By then, the pendulum's swing was very small but the rhythm was not far off from where it started.
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90 minutes
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Good overall, but the expected ratio needs to be specified and compared with your observations.
No need to send a copy of the document, but send me a brief note telling the what the ratio of the times between release and 2d 'hit', and between alternate subsequent 'hits', should be and how this compares with what you observed.