Cavendish Balance, 1L10.30

Location:

• Cabinet: Mechanic (Will be permanently installed in lecture halls)

• Bay: {B12}

• Shelf: "1"

attachment:CavendishBalance.jpg (photo from Pasco online)

Description:

Two small lead balls are supported on a cross-beam which is suspended by a fine wire(glass) to form a torsion pendulum. 2 Large lead spheres are placed opposite the small balls to exert a force onto the suspended system.

• Equipment:	Location	ID Number
  Cavendish Balance	ME, B12, 1	1L10.30
  Laser	...	...

Setup:

1. Currently Setup requires a 48 hour notes before lecture. Once there installed within the room this condition maybe lifted.
2. Make sure the Cavendish Torsion Balance is level on a bench or platform that has no vibration.

Cautions, Warnings, or Safety Concerns:

1. The Large Masses are made of Lead and weight about 1.5Kg
2. The Torsion Balance inside the Cavendish is very delicate and can break.

Demonstration:

The two smaller masses have a mass of m=38g and are made of lead. They are suspended on a cross-beam torsion wire and have a distance of d=50.0mm for center-to-center of each ball. The two larger masses are made of lead too and have a mass of M=1.5Kg

The objective of this experiment is to determine G. F = (GmM)(r^-2). The two large lead spheres are placed opposite the small balls, which will exert a torque and move cross-beam torsion wire system. The system is now allowed to come to a new equilibrium position which is shown by a laser beam reflected off the a small mirror that is attracted to the cross-beam torsion wire system. The reflected laser dot will be on the opposite wall and the motion of the cross-beam can be observed and measured.

Allowed the system to come to an equilibrium position.

The large lead balls are then shifted to the other smaller lead ball to give a torque in the opposite direction. The cross-beam torsion wire system is then aloud to find a new equilibrium as it damped out in a simple harmonic motion. Full damping requires over an hour and a half.

References:

1. [http://store.pasco.com/pascostore/showdetl.cfm?&DID=9&Product_ID=1655&groupID=306&Detail=1 Pasco]

2. [attachment:CavendishManual.pdf Cavendish Manual (pdf)]

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