Talk:Cavendish experiment

From Wikipedia, the free encyclopedia

You have new messages (last change).
WikiProject Physics
Portal:Physics
 Physics Portal
This article is within the scope of WikiProject Physics, which collaborates on articles related to physics.
??? This article has not yet received a rating on the assessment scale. [FAQ]
Top This article is on a subject of Top importance within physics.

Please rate this article, and then leave comments here to explain the ratings and/or to identify the strengths and weaknesses of the article.

Contents

[edit] Requested move: Torsion bar experiment → Cavendish experiment

This experiment is always referred to as the 'Cavendish experiment' and never the 'torsion bar experiment'; see the external links in the article, and:

I could only find one page where it was called something else: Michell-Cavendish Experiment. Also the current name is misleading; the apparatus used is called a 'torsion balance', whereas most people think of a 'torsion bar' as part of a car suspension. How about renaming this well-written article 'Cavendish experiment'? I've already added that name to the article. - Chetvorno 07:36, 1 April 2007 (UTC)

Done. —Nightstallion (?) 20:16, 12 March 2006 (UTC)

[edit] Fourmilab is bogus

The do-it-yourself experiment at Fourmilab ([1]) can't possibly be correct. A calculation using F=MA and F=GmM/(r^2) shows that it would take hours for the torsion balance to rotate as far as the video shows. Furthermore, a version of the experiment performed by Professor Norman Scheinberg (The City College of New York) uses much more massive weights (about 30 kg) and a much thinner wire (25 microns) made of tungsten - and the torsion balance only moved about 2.5 cm in twelve minutes. In the Fourmilab experiment, the movement due to gravity produced by the smaller weights and thicker, stiffer wire would be microscopic. (An earlier version of the article included a remark questioning Fourmilab's results, but it was removed.) If the video is not a hoax, the explanation for the rapid movement is almost certainly air currents created by the movement of his hands near the balance. The experiment by Professor Scheinberg is inside a box to prevent air currents from moving the balance, and Cavendish's original experiment was also protected from wind. - CronoDAS 03:46, 19 August 2006 (UTC)

Correction: Upon closer examination of the video, the torsion bar is actually touching the platform that one of the weights is placed upon. When he moves the weight, the foam shakes, knocking the styrofoam bar away. Furthermore, styrofoam is notorious for accumulating a large static electricity charge. All John Walker found was static electricity, not gravity. - CronoDAS 04:39, 20 August 2006 (UTC)

Although I haven't gone through the math, your criticisms of the 'Fourmilab' experiment sound valid. So glad someone has the experience to catch errors like that. I think I included the Fourmilab page as reference just because I was impressed that someone would try the Cavendish experiment in their basement with fishing line. But I should have noticed he didn't calibrate the apparatus by calculating the period of oscillation. I agree with removing the Fourmilab reference and replacing it with the Scheinberg experiment, a much better example of a homebrew Cavendish experiment. - Chetvorno 08:20, 1 April 2007 (UTC)

[edit] Add a picture

Could an artist please add a picture to illustrate this experiment as it would be so much easier to understand then.82.25.173.16 18:39, 3 December 2006 (UTC)

[edit] Image of Cavendish

What kind of image is the one of Cavendish performing the experiment, and where did it come from? It looks for all the world like a manipulated photograph, but as far as I am aware photography didn't get started until the 1820s, 10 years after his death. Is it just an extremely good rendering? The image file itself doesn't seem to have any source information associated with it.

Retrieved from "http://en.wikipedia.org../../../c/a/v/Talk%7ECavendish_experiment_b44d.html"