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course Phy 201
6/19 around 11:40
Listen to the rhythm of the sounds made by the ball striking the bracket.Do the sounds get closer together or further apart, or does the rhythm remain steady? I.e., does the rhythm get faster or slower, or does it remain constant?
Repeat a few times if necessary until you are sure of your answer.
Insert your answer into the space below, and give a good description of what you heard.
Your response (start in the next line):
The sounds get closer together and the rhythm does not remain constant
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If the bracket is tilted forward a bit, as shown in the figure below, the pearl will naturally hang away from the bracket. Tilt the bracket forward a little bit (not as much as shown in the figure, but enough that the pearl definitely hangs away from the bracket). Keep the bracket stationary and release the pendulum. Note whether the pearl strikes the bracket more and more frequently or less and less frequently with each bounce.
Again listen to the rhythm of the sounds made by the ball striking the bracket.
Do the sounds get closer together or further apart, or does the rhythm remain steady? I.e., does the rhythm get faster or slower, or does it remain constant?
Repeat a few times if necessary until you are sure of your answer.
Insert your answer into the box below, and give a good description of what you heard.
Your response (start in the next line):
The sounds get further apart
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If the bracket is placed on a perfectly level surface, the pearl will hang straight down, just barely touching the bracket. However most surfaces on which you might place the bracket aren't perfectly level. Place the bracket on a smooth surface and if necessary tilt it a bit by placing a shim (for a shim you could for example use a thin coin, though on most surfaces you wouldn't need anything this thick; for a thinner shim you could use a tightly folded piece of paper) beneath one end or the other, adjusting the position and/or the thickness of the shim until the hanging pearl just barely touches the bracket. Pull the pearl back then release it.
If the rhythm of the pearl bouncing off the bracket speeds up or slows down, adjust the level of the bracket, either tilting it a bit forward or a bit backward, until the rhythm becomes steady.

Describe the process you used to make the rhythm steady, and describe just how steady the rhythm was, and how many times the pendulum hit the bracket..
Your response (start in the next line):
I placed one end of an index card under the bracket. When I did this the pearl bounced against the bracket about 4 times at a pretty consistent rhythm.
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On a reasonably level surface, place one domino under each of the top left and right corners of your closed textbook, with the front cover upward. Place the bracket pendulum on the middle of the book, with the base of the bracket parallel to one of the sides of the book. Release the pendulum and observe whether the sounds get further apart or closer together. Note the orientation of the bracket and whether the sounds get further apart or closer together.
Now rotate the base of the bracket 45 degrees counterclockwise and repeat, being sure to note the orientation of the bracket and the progression of the sounds.
Rotate another 45 degrees and repeat.
Continue until you have rotated the bracket back to its original position.
Report your results in such a way that another student could read them and duplicate your experiment exactly. Try to report neither more nor less information than necessary to accomplish this goal. Use a new line to report the results of each new rotation.
Your response (start in the next line):
First, I placed the bracket in the middle of the book with the pearl facing towards the left hand side. I pulled the pearl back and then released it. I observed that it bounced approximately three times. There was a short interval between the last two times before the pearl stopped swinging.
Next, I rotated the bracket counterclockwise 45 degrees. I pulled back and released the pearl and I observed the same results as the previous position.
Next, I rotated the bracket counterclockwise 45 degrees again. I pulled back the pearl and released it. At first, it repeated the same pattern as the previous positions, but then started to swing slightly right to left.
I rotated the bracket counterclockwise 45 degrees again. After the pearl was pulled and released it bounced against the bracket. But, then the pearl started to swing back and forth in a constant rhythm without touching the bracket.
I rotated the bracket 45 degrees again in the counterclockwise position. After I released the pearl it bounced against the bracket twice. However, the second bounce was slower than the first bounce. Then the pearl started to swing back and forth in a constant rhythm without touching the bracket.
The bracket was rotated 45 degrees again. After the pearl was released I observed it bounced against the bracket three times. Each bounce was slower than the one before it. Then the pearl started swinging back and forth in a constant rhythm without touching the bracket.
The bracket was once again rotated 45 degrees. The pearl was released and it bounced against the bracket very rapidly. I noticed it was getting faster with each bounce.
I rotated the bracket 45 degrees once more. The pearl bounced against the bracket approximately 4 times. The last two bounces were close together. The pearl then stopped swinging.
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Describe how you would orient the bracket to obtain the most regular 'beat' of the pendulum.
Your response (start in the next line):
I would personally orient the bracket at the 180 degrees position. It is at this position that I noticed the most consistent and regular beat.
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Orient the bracket in this position and start the TIMER program. Adjust the pendulum to the maximum length at which it will still bounce regularly.
Practice the following procedure for a few minutes:
Pull the pendulum back, ready to release it, and place your finger on the button of your mouse. Have the mouse cursor over the Click to Time Event button. Concentrate on releasing the pendulum at the same instant you click the mouse, and release both. Do this until you are sure you are consistently releasing the pendulum and clicking the mouse at the same time.
Now you will repeat the same procedure, but you will time both the instant of release and the instant at which the pendulum 'hits' the bracket the second time. The order of events will be:
click and release the pendulum simultaneously
the pendulum will strike the bracket but you won't click
the pendulum will strike the bracket a second time and you will click at the same instant
We don't attempt to time the first 'hit', which occurs too soon after release for most people to time it accurately.
Practice until you can release the pendulum with one mouse click, then click again at the same instant as the second strike of the pendulum.
When you think you can conduct an accurate timing, initialize the timer and do it for real. Do a series of 8 trials, and record the 8 time intervals below, one interval to each line. You may round the time intervals to the nearest .001 second.
Starting in the 9th line, briefly describe what your numbers mean and how they were obtained.
Your response (start in the next line):
.557
.473
.532
.584
.391
.484
.601
.498
The above values are the times it took the pearl to hit the bracket the second time once it was released. The values are expressed in seconds.
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Finally, you will repeat once more, but you will time every second 'hit' until the pendulum stops swinging. That is, you will release, time the second 'hit', then time the fourth, the sixth, etc..
Practice until you think you are timing the events accurately, then do four trials.
Report your time intervals for each trial on a separate line, with commas between the intervals. For example look at the format shown below:
.925, .887, .938, .911
.925, .879, .941
etc.
In the example just given, the second trial only observed 3 intervals, while the first observed 4. This is possible. Just report what happens in the space below. Then on a new line give a brief description of what your results mean and how they were obtained.
Your response (start in the next line):
.5, .625, .262
.453, .535
.730, .5
.5, .422, .410, .312
.480, .422, .410
.730, .172
.535, .589
.453, .578, .324
Each line represents one trial. The values in each line are the time intervals between each bounce off the bracket. I conducted eight trials and as you can see some trials had more bounces than other trials.
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Now measure the length of the pendulum. (For the two-pearl system the length is measured from the bottom of the 'fixed' pearl (the one glued to the top of the bracket) to the middle of the 'swinging' pearl. For the system which uses a bolt and magnet at the top instead of the pearl, you would measure from the bottom of the bolt to the center of the pearl). Using a ruler marked in centimeters, you should be able to find this length to within the nearest millimeter.
What is the length of the pendulum?
Your response (start in the next line):
14.45 cm
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If you have timed these events accurately, you will see clearly that the time from release to the second 'hit' appears to be different than the time between the second 'hit' and the fourth 'hit'.
On the average,
how much time elapses between release and the second 'hit' of the pendulum,
how much time elapses between the second and fourth 'hit' and
how much time elapses between the fourth and sixth 'hit'?
Report your results as three numbers separated by commas, e.g.,
.63, .97, .94
Your response (start in the next line):
.164, .11, there wasn’t a sixth
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A full cycle of a free pendulum is from extreme point to equilibrium to opposite extreme point then back to equilibrium and finally back to the original extreme point (or almost to the original extreme point, since the pendulum is losing energy as it swings)..
The pearl pendulum is released from an 'extreme point' and strikes the bracket at its equilibrium point, so it doesn't get to the opposite extreme point.
It an interval consists of motion from extreme point to equilibrium, or from equilibrium to extreme point, how many intervals occur between release and the first 'hit'?
Your response (start in the next line):
One
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How many intervals, as the word was described above, occur between the first 'hit' and the second 'hit'? Explain how your description differs from that of the motion between release and the first 'hit'.
Your response (start in the next line):
Two, because it hits the bracket and goes back to the extreme, which is the first interval and then it hits the bracket again making the second interval
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How many intervals occur between release and the second 'hit', and how does this differ from the motion between the second 'hit' and the fourth 'hit'?
Your response (start in the next line):
Three, because it goes from extreme position to equilibrium, equilibrium to extreme, and the finally extreme to equilibrium again.
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How many intervals occur between the second 'hit' and the fourth 'hit', and how does this differ from a similar description of the motion between the fourth 'hit' and the sixth 'hit'?
Your response (start in the next line):
Four, because it goes from equilibrium to extreme, extreme to equilibrium, equilibrium to extreme, extreme to equilibrium
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Why would we expect that the time interval between release to 2d 'hit' should be shorter than the subsequent timed intervals (2d to 4th, 4th to 6th, etc.)?
Your response (start in the next line):
We would expect to be shorter because the hits become further spaced out as the pendulum’s rhythm becomes regular. However, my experiment did not correctly exemplify this statement. I’m guessing there was some human error.
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Would we expect additional subsequent time intervals to increase, decrease or stay the same?
Your response (start in the next line):
Time intervals should increase because the pendulum will begin to swing slower and slower over time.
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What evidence does this experiment provide for or against the hypothesis that the length of a pendulum's swing depends only on its length, and is independent of how far it actually swings?
Your response (start in the next line):
We didn’t compare lengths so we really can’t determine this from this experiment. Unlike, the pendulum experiment were we shortened the length of the pendulum.
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Your instructor is trying to gauge the typical time spent by students on these experiments. Please answer the following question as accurately as you can, understanding that your answer will be used only for the stated purpose and has no bearing on your grades:
Approximately how long did it take you to complete this experiment?
Your response (start in the next line):
Roughly 1 hour and 30 min"
&#Very good data and responses. Let me know if you have questions. &#