PASCO AP-8215A Gravitational Torsion Balance - Manual (Page 7)

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M o d e l N o . A P - 8 2 1 5 A E q u i p m e n t S e t u p
3
Equipment Parameters
• Small tungsten balls
Mass: 38.3 g ±0.2 g (m
2
)
Radius: 8.19 mm
Distance from ball center to torsion axis: d = 50.0 mm
• Large tungsten balls
Mass: 1500 ±10 g (m
1
)
Radius: 27.6 mm
• Distance from the center of the large ball to the center of mass of
the small ball when the large ball is against the aluminum plate
and the small ball is in the center position within the case: b =
46.5 mm. (Note: Tolerances may vary depending on the accuracy
of the horizontal alignment of the pendulum.)
• Distance from the surface of the mirror to the outer surface of the
glass window: 11.4 m
• Torsion Ribbon
Material: Beryllium Copper
Length: approximately 260 mm
Corss-section: 0.017 by 0.150 mm
Equipment Setup
Initial Setup
1. Place the support base on a flat, stable table that is located
such that the Gravitational Torsion Balance will be at least 5
meters away from a wall or screen.
Note: For best results, use a very sturdy table, such as an optics
table.
2. Carefully remove the Gravitational Torsion Balance from the
box, and secure it in the base.
3. Remove the front aluminum plate by removing the thumb-
screws (Figure 3), and carefully remove the packing foam
from the pendulum chamber.
Note: Save the packing foam, and reinstall it each time the Gravi-
tational Torsion Balance is transported.
4. Fasten the clear plastic plate to the pendulum chamber with
the thumbscrews.
Note: Do not touch the mirror on the pendulum.
IMPORTANT NOTES
1. The Gravitational Torsion Bal-
ance is a delicate instrument. We
recommend that your set ip up in a
relatively secure area where it is
safe from accidepnts and from
those who don’t fully appreciate
delicate instruments.
2. The first time you set up the tor-
sion balance, do so in a place
where you can leave it for at least
one day before attempting mea-
surements, allowing time for the
slight elongation of the torsion rib-
bon that will occur initially.
3. Keep the pendulum bob secured
in the locking mechanisms at all
times, except while setting up and
conducting experiences.
At ta ch to
Ea rth Gr ou nd .
GRA
VIT AT IONAL
TORSION
BALANCE
AP -8 21 5
Figure 3: Removing a plate from
the chamber box
Aluminum plate
Pendulum
chamber
Pendulum
bob