pearl pendulum

Your work on pearl pendulum 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'

The sounds get closer together, like a car motor starting.

Your description of the rhythm of the pendulum when tilted 'forward'

The sounds get further apart, like a car motor dying.

Your description of the process used to keep the rhythm steady and the results you observed:

The sounds seem equal for about 7-8 taps, then there is a jumbled bunch of soft taps as the pendulum comes to rest.

Your description of what happened on the tilted surface, rotating the system 45 degrees at a time:

With the bracket on top of the book and parallel to the sides of the book which is elevated with two dominos, the pendulum is hanging away from the bracket, therefore, the pendulum taps get futher apart until stopping after about 8 taps.

At 45 degrees, I can hear about 11 taps before they stop.

At 90 degrees, I can hear about 15 taps before they stop.

At 135 degrees, I hear more taps than I can count, because the pendulum is completely resting against the bracket in this position.

180 degrees gives the same results as 90 degrees.

225 degrees gives the same results as 45 degrees.

Your description of how you oriented the bracket on the tilted surface to obtain a steady rhythm:

The most regular beat occurs at 90 and 180 degrees, where the pendulum is neither resting against nor hanging away from the bracket.

Your report of 8 time intervals between release and the second 'hit':

.656

.609

.641

.500

.641

.515

.531

.609

Your report of 4 trials timing alternate hits starting with the second 'hit':

.531, .719, .656, .750

.625, .703, .656, .781

.531, .625, .640, .641

.562, .640, .625, .656

The length of your pendulum in cm (you might have reported length in mm; the request in your instructions might have been ambiguous):

10.5cm

Your time intervals for alternate 'hits', starting from release until the pendulum stops swinging:

.562, .672, .644

Your description of the pendulum's motion from release to the 2d hit:

The pendulum descends from 90 degrees and strikes the bracket.

Your description of the pendulum's motion from the 2d hit to 4th hit:

The pendulum richochets off the bracket, rises to about 45 degrees, then falls and hits the bracket again.

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 pendulum rises to a lesser angle before falling and hitting the bracket again, taking seemingly longer than the first interval.

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:

The pendulum rises to a lesser angle before falling and hitting the bracket again, seeming equal in time to the previous interval.

Your conjecture as to why a clear difference occurs in some intervals vs. others:

During the first time interval, the pendulum begins by falling from the suspended position, unlike during subsequent time intervals, when the pendulum first ricochets away from the surface of the bracket and rises to its peak before falling again, thus spending more time away from the surface of the bracket.

What evidence is there that subsequent intervals increase, decrease or remain the same:

In this position, the subsequent intervals appear to remain about the same until the amplitude becomes so short that the pendulum comes to rest against the surface of the bracket. In the absence of this dissipative force, we would expect subsequent intervals to remain the same indefinitely.

What evidence is there that the time between 'hits' is independent of the amplitude of the swing?

Because the time interval between subsequent swings remains nearly equal until the pendulum comes to rest, even though the amplitude of the swing decreases each time, it appears to support the hypothesis that the length of a pendulum's swing depends only on its length and is independent of how far it actually swings.