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Gravitational Torsion Apparatus Information

This page contains important information about the use of the Gravitational Torsion Balance commonly used in PHY 266. The apparatus is a Pasco AP-8215A. Below you will find links to the user manual and suggested experiments.

IMPORTANT! DO NOT MOVE THE BALANCE WITHOUT LOCKING THE PENDULUM ARM FIRST! Always lock the pendulum when the apparatus is not in use.

Figure 3
The pendulum is suspended by a very fragile ribbon of wire and is easily broken. Do not attempt to adjust the height of the pendulum bob. Only level and zero the pendulum. If you have any questions about use, please see Eric Chapman in Olin 110.

Equipment Parameters

  • Small tungsten balls
    • Mass: 38.3 g +/- 0.2 g (m2)
    • Radius: 8.19 mm
    • Distance from ball center to torsion axis: d = 50.0 mm
  • Large lead balls
    • Mass: 1500 g +/- 10 g (m1)
    • Radius: 31.9 mm
  • Distance from the center of mass 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 (Tolerances will 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 mm
  • Torsion Ribbon Material: Beryllium Copper
    • Length: approx. 260 mm
    • Cross-section: .017 x .150 mm


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