pearl pendulum

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Phy 201

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' **

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 goet closer together as time goes by. This is more noticable towards the very end of them movement, because the sounds are very close together right before the pearl stops.

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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 folded a thin piece of paper three times and put it under the very front of the bracket. The rhythm is steady and consistent with various trials. The pendulum hits the bracket about 11 times each time.

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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):

With the pearl facing me, so the bracket is on a downward slant, the sounds sound very consistent but definitely get closer together by the end of the movement of the pearl.

With the pearl facing at and angle towards the bottom right of the book, the sounds seem to slow down.

With the pearl pointing directly towards the right side of the book, the sounds seem to speed up as the movement continues.

With the pearl facing the top right corner of the book, the sounds speed up and the amount of hits are less. The pearl speeds up faster and ends earlier than in previous orientations.

With the pearl directly facing away from me, towards the top of the book, the pearl seems to speed up more rapidly than before and come to a close, but not as quickly as it did when facing the top right corner of the book.

With the pearl facing the top left of the book, the pearl speeds up especially before coming to a stop.

With the pearl directly facing the left side of the book, the pearl seems to move pretty consistently but speeds up right before ceasing movement.

With the pearl facing the bottom left corner of the book, it seems to slow down as movement continues.

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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 have the pearl directly oriented towards me.

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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):

.488

.402

.418

.371

.344

.480

.320

.449

These numbers are the time intervals of the time between from when the pearl was dropped, hit the bracket once, came back up, and hit the bracket for a second time.

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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):

.445, .546, .563

.406, .430, .508, .672

.461, .477, .492, .531

.430, .453, .534, .563

These results are the time intervals between every second hit of the pearl to the bracket from the start of movement.

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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):

9.42 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):

.436, .477, .524

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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):

Half of an interval????

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@& The 'pearl' goes from extreme point to equilibrium between release and the first 'hit'. How long in an interval, as defined here? Can you revise your answer accordingly?*@

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???? Between the second hit and he fourth hit the pearl goes back up to the extreme point (.5), then back down (.5), then back up (.5), then back down (.5).

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@& What is the definition of an 'interval' in this series of questions? How does that fit with your description?*@

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):

1.5 It doesn't go back up or back down.

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@& You're on the right track, but it doesn't appear that you're using the current definition of 'interval' quite carefully enough.*@

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):

Two

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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):

It doesn't have to use the momentum gained from bouncing off of the bracket to complete any intervals, just the drop.

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@& The answer here will depend on a careful interpretation of the word 'interval' as used above.*@

Would we expect additional subsequent time intervals to increase, decrease or stay the same?

your response &&&&&&&&&&&&&&&&&&

(start in the next line):

Decrease, because the extreme point will start to be lower and closer to the equilibirum point.

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@& If you set the system up for a consistent rhythm, then these intervals should not change.*@

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):

This goes against the hypothesis because the length of the swing also depends on how far it swings, because the closer the extreme point became to the equilibirum with each time interval, the shorter the time intervals would become.

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@& Your answer should be based on your data, as opposed to assumptions.*@

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):

About 1 hour.

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*#&!

@& You appear to have good data, and it shouldn't take you long to make the necessary revisions.

&#Please see my notes and, unless my notes indicate that revision is optional, submit a copy of this document with revisions and/or questions, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).
Be sure to include the entire document, including my notes.
If my notes indicate that revision is optional, use your own judgement as to whether a revision will benefit you.