Fig. 4. Foucault pendulum
plane of oscillation versus time.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.
1995. These
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.
Fig. 4. Foucault pendulum
plane of oscillation versus time.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.