In my prior blog posts, I’ve presented methods for constructing ellipses using Web Sketchpad and paper folding. The other conic sections are feeling a bit left out, so let’s explore some techniques for constructing parabolas.

All three Web Sketchpad models below (and here) are based on the distance definition of a parabola: The set of points equidistant from a fixed point (the *focus*) and a fixed line (the *directrix*).

Experiment with the interactive models and think about why they generate parabolas. The rhombus construction is based on an illustration found in the 17th-century Dutch mathematician Frans van Schooten’s manuscript, *Sive de Organica Conicarum Sectionum in Plano Descriptione, Tractatus* (*A Treatise on De**vic**es for Drawing Conic Sections*). Van Schooten’s beautiful picture is below.