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5
Rotational Alignment of the Pendulum Bob Arms
(Zeroing)
The pendulum bob arms must be centered rotationally in the case
— that is, equidistant from each side of the case (Figure 7). To
adjust them:
1.
Mount a metric scale on the wall or other projection surface
that is at least 5 meters away from the mirror of the
pendulum.
2.
Replace the plastic cover with the aluminum cover.
3.
Set up the laser so it will reflect from the mirror to the
projection surface where you will take your measurements
(approximately 5 meters from the mirror). You will need to
point the laser so that it is tilted upward toward the mirror
and so the reflected beam projects onto the projection surface
(Figure 8). There will also be a fainter beam projected off the
surface of the glass window.
Note:
Vertical adjustment is only necessary at initial setup and
when you change the torsion ribbon or if someone has loosened
the retaining screw by mistake; it is not normally done during
each experimental setup.
L
Figure 8
Setting up the optical lever
SIDE VIEW
TOP VIEW
L
laser
reflected beam
(from mirror)
screen with scale
Figure 7
Aligning the pendulum bob rotationally
TOP, CUTAWAY VIEW
small mass
case plates
The pendulum bob arm
must be centered
rotationally between the
plates.
Summary of Contents for AP-8215
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