Description: A Cavendish Balance.

We have a Leybold Cavendish Balance attached to the wall of the second year lab. This is a small piece of equipment which works well in a laboratory setting. It may be taken to a lecture but owing to our inability to ensure the safety of the apparatus during the time it requires to settle and that it takes more than 60 minutes to record the data it is not recommended that the experiment be attempted.

The recommended procedure is to show the balance and then to show a video of the procedure. Some things are just better done in the lab.

Videos available:

1. Video Encyclopedia Disc 7, Ch 23 (frames 32491 to 35036)

The segment is well described in notes accompanying the disc.
The Leybold apparatus, exactly like the one we use, is shown and there is a terrific animation of the apparatus and the moving spot.

2. Miller Collection: Measurement of G The Cavendish Experiment (disc, 2 minutes 15 seconds, or film loop)

The film is well described in notes accompanying the disc.
"Time-lapse photography of damped torsional oscillation of moving system after external masses are shifted. Detailed analysis of systematic errors. Calculation of mass of earth."
The Leybold apparatus was used, with several modifications.

3. PSSC Film "Forces" - Zacharias (VHS, black and white, 23 minutes)

Includes the Cavendish experiment using a balance made with two bottles of water for the weights on the bar and two boxes of sand. A classic.

4. Cinema Classics Disc1, Side B, Ch47

excerpts from Zacharias "Forces": stills of the setup and shots of the spot moving (frames 38009 to 39088) and from Miller (frames 39089 to 39478)

Cautions: Handle the Leybold apparatus with great care.

Concepts demonstrated:

Setup Time: Short

Difficulty/Commitment: Straightforward

Visibility: The model is visible.

Related demonstrations:

References: PIRA 1L10.10 (model); 1L10.30 (real thing)
Video Encyclopedia 07-23
Cavendish's paper is on file in the second year lab.