| Blondeau Christophe, Bugada Bruno,
de Vomecourt Quentin, Vieille Petit Jean-Philippe, élèves et Monsieur Jean-Michel Jussiaux, Professeur de Physique Lycée Xavier Marmier, 53, rue de Doubs, 25 300 Pontarlier, France |
Pontarlier, December 10th 2000
Dear Madam,Dear Sir,
During the French « Olympiades » of Physics, we presented at the « Palais de la Découverte », in Paris , France, on November 25th, an original plane which seems to have quite interested the jury.
We wanted to measure approximately the Universal gravitational constant and this in less than a whole minute. When giving the prizes, the President of the Jury, Mr Pierre Lena, member of the French Academy of Sciences, said that our measure was convincing.
Our assembly, inspired by the Cavendish one, can be significantly improved, because it didn’t include any system to stop the vibrations, was set on the floor, and the fibre axle was a nylon one.
It can be used either to measure G, or to demonstrate the change of the gravity centres’medium position of the mobile masses, as we bring nearer external masses, including the audience’s. Its reaction time is considerably lower than ten seconds for the time being.
We join with this letter a recording that we made in an insulated laboratory which could certainly be performed again in a public place with more sophisticated materials.
If you decided to show your visitors this assembly, we would be very interested, and very happy to collaborate.
This letter has been sent to several European Scientific Museums, to
schools for future teachers, to the « Virgo »European Laboratory,
as well as to the Leybold firm which makes high quality scientific material.
If your answer were positive, we would connect you with the other interested
organisms, in order to exchange ideas for the improvement of our assembly..
Yours sincerely
The teacher and his student group of scientific class.
We have conceived an apparatus allowing us to measure the universal
gravitation constant, both quickly and in the audience's presence, easily
performed and likely to interest every physics teacher in Europe. It is
a Cavendish device, to which we have added an electronic servomechanism
enabling us to damp the torsion bar and to measure its rotation. It can
still be improved.
Its detailed description and the source code of the software performing the experiment are available on http://perso.wanadoo.fr/jussiaux.software/.
We can observe a systematic error (shifting) of our results, compared
with the accepted value of G, and we are trying to find the reason why,
by means of a computer simulation using a Runge Kutta algorithm.
Vous vous souvenez que nos résultats, très proches
de ceux du groupe de professeurs américains (rappelons que notre
méthode est physiquement voisine, mais que le traitement informatique
des résultats permet un gain de temps de mesure important), sont
entachés d'une erreur systématique.
Nous nous sommes demandés si cela n'était pas dû au montage lui-même et notamment à sa dissymétrie.
La résolution littérale d'un système d'équations approchées dans Mathematica apporte la réponse : NON. Au contraire, cette dissymétrie crée une erreur systématique de 2%, mais dans l'autre sens ; le couplage entre les oscillations de torsion (qui nous intéressent) et les oscillations de type pendule pesant, modifie les périodes de chaque type d'oscillation.
Si vous voulez en savoir plus, veuillez contacter l'auteur de ce site, qui publiera alors le travail sous Mathematica.
63 groupes participaient à ce concours. Les thèmes
abordés couvraient les domaines de la Physique bien sûr, mais
aussi