After an initial period of testing, modification and adjustment of our
pendulum, the data recorded in Fig. 4 were taken in the early part of Dec.
measurements show that the average turning rate of the pendulum is nearly equal to the predicted we' = 10.36º/hr. The origin of the random fluctuations and the small drift, an advance in angle over the expected by about 0.5º/day, is not understood. On the other hand, the variations of the turning rate with an apparent period between 8 and 9 hours seen in Fig. 4 are directly correlated with the direction of the plane of oscillation of the pendulum and arise from small imperfections in the pendulum wire support and holder. Details of this effect are given in the Foucault pendulum description below. Here we just note that their practical effect is to make the turning rate deduced from a few hours of observation vary anywhere from about 9 ½ to 11º/hr.
The crosses are measurements of the pointer position relative to the
expected position moving at 10.36º/hr from some arbitrary origin.
The several fits to this data
are as follows: The straight line is the mean turning rate observed as a relative forward drift of 0.5º/day or an absolute rotation rate of 10.38º/hr. The apparently
randomly wandering curve is the data smoothed on a timescale of a day and superimposed on this is a more rapidly varying function that fits those changes in
pendulum rate that are periodic in the direction of the plane of oscillation.
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