Quadrature. N° 83. p. 34-36. Triangle de Reuleaux tourné.

English Title : The rotated Reuleaux triangle. (ZDM/Mathdi)

Auteur : Truc Jean-Paul

Résumé

Dans cet article, l’auteur propose de calculer explicitement un paramétrage du sphéroforme obtenu en faisant tourner un triangle de Reuleaux autour de son axe de symétrie, puis de calculer son volume et sa surface.

Abstract

Using a suitable parametrization in terms of polar coordinates, the author computes the volume and the surface area of the solid of revolution obtained by rotating a Reuleaux triangle of constant width R about one of its axes. They are respectively given by Cal V=(frac 2 3 π- frac{π^2}{6}) R^3 and Cal S=frac{πR^2}{3} (6 – π). Computation of the volume is accomplished by finding the x-coordinate of the center of mass and invoking the well-known theorem of Pappus-Guldin, according to which the volume is given as the product of the circumference of the circle traversed by the center of mass and the area of the region being revolved (in this case half of the Reuleaux triangle). For the surface area a formula of Blaschke relating Cal V and Cal S for a solid of constant thickness R, viz. Cal S=frac{RCal S}{2} – frac{πR^3}{3}, is used. The result for the volume is compared with the volume of the solids of Meissner [{it B. Kawohl} and {it C. Weber}, Math. Intell. 33, No. 3, 94-101 (2011; Zbl 1231.52002)], which are believed to have minimal volume among all solids of constant thickness R. The paper contains several pesky typos – extra factor cos (t) in the parametrization of y(t), wrong power R instead of R^3 in the expression for the center of mass and the missed coefficient 3 of Cal V in one of the formulas for Cal S. (ZDM/Mathdi)

Notes

Quadrature est un magazine de mathématiques pures et appliquées. Il s’adresse aux enseignants, étudiants, ingénieurs et amateurs de mathématiques.
Tout internaute peut acheter le numéro en cours et les anciens numéros sur la site de la revue quadrature.info (ISSN de l’édition électronique : 1760-4826).

Données de publication

Éditeur Quadrature Revigny-sur-Ornain , 2012 Format A4, p. 34-36 Index Bibliogr. p. 36-36
ISSN 1142-2785

Public visé élève ou étudiant, enseignant, tout public Niveau licence Âge 18, 19, 20

Type article de périodique ou revue, vulgarisation, popularisation Langue français Support papier

Classification