Sources of Cavendish Torsion Balances and Gravity Meters:
Pasco Scientific: The picture shown at the right is of their model AP-8215 Gravitational Torsion Balance. Visit their webpage at URL:
TEL-Atomic Incorporated: Their Computerized Cavendish Balance w/ Control Box is model number TEL RP2011. Visit their website at URL:
Leybold Didactic GmbH: The latest version of their Gravitation Torsion Balance is product number 332 101, with optional IR Position Detector 332 11, and replacement 1 metre Torsion Strip F.33210. Downloadable instruction sheets in *.pdf format are available in their Scientific Education section (332101de.pdf for German and English, 332101fr.pdf for French and Spanish) at their website at URL:
http://www.leybold-didactic.de/data_e/service/index.html?manuals.html
LaCoste and Romberg: High accuracy gravity meters used in geodetic surveys (and recently in measuring solar eclipse gravity anomalies). Visit their website at URL:
http://www.lacosteromberg.com/
Informative Links:
Eot-Wash Group: The University of Washington Eot-Wash Group has arguably made the highest accuracy measurement of the Newtonian gravitational constant G. The value that they reported for G at the April 2000 APS Meeting was G = 6.67390(9)x10-11 m3 kg-1 s-2. [The current value recommended by CODATA is G = 6.67259(85)x10-11 m3 kg-1 s-2.] They are also undertaking measurements of gravity at the submillimeter scale. Visit their website at URL:
http://www.npl.washington.edu/eotwash/index.html
Bending Spacetime in the Basement: Cool link with motion pictures (disputed) of a home made torsion pendulum.
http://www.fourmilab.ch/gravitation/foobar/
Wikipedia entry on the Cavendish experiment: General discussion with history and links.
http://en.wikipedia.org/wiki/Torsion_bar_experiment
Norman Scheinberg's Cavendish Experiment: Amateur Cavendish experiment with mathematics confirmation of results.
http://www.sas.org/tcs/weeklyIssues_2005/2005-07-01/feature1/index.html
Treasure Trove of Physics: Pendulum mathematics info.
http://www.treasure-troves.com/physics/Pendulum.html
University of Manitoba (UM): Byron Southern of the UM has put together a nice chapter (from a larger course) entitled "Angular SHM Torsion Pendulum" which can be accessed as a slide show at URL:
http://www.physics.umanitoba.ca/~souther/waves/chap16c/index.htm
Alternately, the entire presentation can be downloaded as a single short Adobe Acrobat file. (Use: Shift-left-Mouse-button to download the following file using the Netscape browser.)
http://www.physics.umanitoba.ca/~souther/waves/chap16c.pdf
International Tungsten Industry Association (ITIA): Tungsten (also known as Wolfram) is one of the heaviest metals, with a density of 19.25 g/cm3. In fact, it is 69.6% greater in density than lead (which has a density of 11.35 g/cm3). Although gold has almost exactly the same density as tungsten, it is over an order of magnitude more expensive. Therefore, tungsten has been found to be ideal for high precision measurements of the gravitational constant G, and was even used by G. G. Luther and W. R. Towler in their measurement of G (which is currently the accepted value).[See the downloadable bibliography below.] Read the info on tungsten as provided by the ITIA via the link below:
http://www.itia.org.uk/tungtext1.htm
Solar Eclipse Gravity Variations:
Following some unusual measurements made with a Foucalt pendulum in 1954 and 1959 by Maurice Allais, researchers Erwin J. Saxl and Mildred Allen made measurements at Harvard University (using a torsion pendulum) of an unusual variation of the gravitational acceleration during a solar eclipse in 1970.[See the downloadable bibliography below.] The effect is apparently repeatable in the sense that it has been measured on several occasions. See the following links for more info.
http://www.science-frontiers.com/sf074/sf074a05.htm
http://www.science.nasa.gov/newhome/headlines/ast06aug99_1.htm
NOAA, Our Restless Tides: A link on the earth's tides:
http://co-ops.nos.noaa.gov/restles3.html
A new experiment was recently reported in Phys. Rev. D 62, 041101(R) (2000), by Qian-shen Wang et al., which used a LaCoste and Romberg Gravity Meter to precisely measure this variation in the gravitational acceleration during an eclipse. It was speculated that there might be a gravitational shielding effect during an eclipse.
Downloadable Bibliography:
A short bibliography to get you started, in postscript readable and laser printable *.ps format, entitled "Cavendish Torsion Pendulum and Newtonian Gravitational Constant Bibliography." The following document was typeset by the author using LaTeX 2e and REVTeX v3.1. (Use: Shift-left-Mouse-button to download under Netscape.)
Cavendish.ps 49.5 kB
Return to the home page of my web site at URL:
http://www.physics.mq.edu.au/~dalew/