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: **
I was not provided any copper wire in my kit, so I had to use thread. The thread worked well, but threading it through the pearl was a bear - it took almost 20 minutes just to do that.
** Your description of the rhythm of the pendulum when tilted 'back' **
The pearl stricks the bracket more and more frequently - that is, the sound of the pearl striking the bracket becomes closer and closer together. The ting sound of the ball striking the bracket became progressively closer together as clock time increased.
** Your description of the rhythm of the pendulum when tilted 'forward' **
The rhythm of the pearl striking the bracket is again getting faster at first. However, a point is reached where the rhythm starts to become slower and the intervals in between stikes of the bracket become farther apart.
** Your description of the process used to keep the rhythm steady and the results you observed: **
Starting with the bracket level, I released the pearl and the strikes were speeding up as clock time increased. I then pitched the front of the bracket forward until the pearl was striking with constant intervals and a steady rhythm. I would estimate the bracket was pitched forward approx. 30 degrees give or take 5 degrees.
** Your description of what happened on the tilted surface (textbook and domino), rotating the system 45 degrees at a time: **
Starting with the book elevated from back to front, I placed the bracket such that the side with the pearl faced the bottom edge of the book - facing down the incline. Releasing the pearl, the sounds resonated with increasing speed, but fairly regular. Rotating 45 degrees, so that the bracket now faced the bottom right corner, I repeated the exercise, noting that it was almost exactly the same. I then rotated another 45 degrees so that the bracket was not facing the right edge of the book. Repeating the exercise, I noted a slight increase in the rhythm, but not by much. I continued all the way around the book, rotating by 45 degrees until I had made a complete 360 degree revolution, noting that the pearl strikes were quicker and closer together when the bracket faced the top of the top.
** Your description of how you oriented the bracket on the tilted surface to obtain a steady rhythm: **
In order to obtain the most regular rhythm, the bracket should be oriented facing the bottom edge of the book, such that the sides of the bracket are parallel to the sides of the book.
** Your report of 8 time intervals between release and the second 'hit': **
0.518
0.520
0.594
0.543
0.453
0.465
0.531
0.543
The numbers are recorded in seconds and are taken from the moment the pearl is released until it strikes the bracket a 2nd time. I obtained them by pressing the mouse button with my right hand while releasing the pearl with my left hand.
** Your report of 4 trials timing alternate hits starting with the second 'hit': **
0.723, 0.762, 0.953, 0.969, 1.025
0.684, 0.816, 0.953, 0.969, 1.094
0.688, 0.859, 1.078, 1.063
0.703, 0.813, 0.938, 1.000, 1.025
The results are recorded in seconds. They represent the clock time interval between every other hit (or every 2nd hit) of the pearl on the bracket. I again, hit the timer button with my right hand, while releasing the pearl with my left hand.
** The length of your pendulum in cm (you might have reported length in mm; the request in your instructions might have been ambiguous): **
7.3 cm
** Your time intervals for alternate 'hits', starting from release until the pendulum stops swinging: **
0.70, 0.813, 0.981, 1.000
** Your description of the pendulum's motion from release to the 2d hit: **
0.5 intervals from extreme point to equilibrium
** Your description of the pendulum's motion from the 2d hit to 4th hit: **
1 interval.
Between the first hit and second hit, the pearl has swung from the bracket back to the extreme point, and then back to the equilibrium (or bracket), completing 1 cycle.
** 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: **
1.5 intervals.
The motion between the second and fourth hits differs because it is more regular at that point then between release and 2nd hit.
** 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: **
2 intervals.
The motion between the 2nd and 4th and the 4th and 6th differ only slightly in the regularity of the hits (or the rhythm of the hits).
** Your conjecture as to why a clear difference occurs in some intervals vs. others: **
I am unsure why we expect this to be so. I imagine it has something to do with a steeper release translating into more velocity, but may have something to do with it's motion not being impeded by any object until it strikes the first bracket, whereas subsequent intervals are taken after the pearl has stuck the bracket multiple times, with each strike decreasing it's energy slightly.
Any insight you can provide here would be much appreciated.
You noted that there were 1.5 intervals between release and first 'hit', while there were 2 intervals between the 2d and 4th 'hit'. If the intervals are defined as the instructions described them the numbers would be 3 and 4, but either way the of the number of intervals is 4 to 3.
If the pendulum is in a steady rhythm, each interval should take the same time as any other, so the ratio of the times should be 4 to 3.
** What evidence is there that subsequent intervals increase, decrease or remain the same: **
We expect subsequent time intervals to increase in time between hits and become more regular.
** What evidence is there that the time between 'hits' is independent of the amplitude of the swing? **
This experiment provided evidence that the pendulum's swing depends on its length and on how far it swings, because we noted that the first or second strike of the pearl on the bracket occurred at a more frequent pace then that of the 4th or 6th or 8th strike.
** **
90 minutes
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