The ellipse and its evolute and the distance problem

 Frederick Hartmann and Robert Jantzen
Department of Mathematical Sciences, Villanova University

4-mar-2004

[about 110K with output removed, about 3.4 MEG when executed]

Abstract.  Inspired by a simple max/min distance problem from a calculus course, we were naturally led to explore the geometry of the evolute of an ellipse, ignorant of many classical results that we later found by web/library searching. This is a beautiful example of how, empowered by a computer algebra system, one can follow one's nose so to speak in uncovering elegant mathematical structure that would otherwise be unreachable in practice. A knowledge of parametrized plane curves and their geometry as covered in a typical multivariable calculus course is assumed, including the osculating circle which is not typically covered but which requires little extra effort. It is not necessary to understand the MAPLE graphing code: its purpose is to visualize the geometry and allow user interaction.

a calculus max/min distance problem
leads to counting the normals

describing an ellipse

visualizing the problem

loading the vec_calc package

animated ellipse with evolute

normal lines which pass through a given point

explicit equations for the evolute of an ellipse

number of normals passing through a given point:
root analysis

the hyperbolas of Apollonius

bonus: evolute as the envelope of normals
and the locus of singularities of the family of parallels
(graphical)

bonus: evolute as the curve of limiting
intersections of successive normals (symbolic)

references and web links

generalizations?