A Spiral Bicycle Track that Can Be Traced by a Unicycle

Fuente: arXiv
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Autore principale: Wagon, Stan
Natura: Preprint
Pubblicazione: 2025
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author Wagon, Stan
author_facet Wagon, Stan
contents A unibike curve is a track that can be made by either a bicycle or a unicycle. More precisely, the end of a unit tangent vector at any point on a unibike curve lies on the curve (so the bike's front wheel always lies on the track made by the rear wheel). David Finn found such a curve in 2002, but it loops around itself in an extremely complicated way with many twists and self-intersections. Starting with the polar square root curve r = sqrt[t/(2 pi)] and iterating a simple construction involving a differential equation apparently leads in the limit to a unibike curve having a spiral shape. The iteration gets each curve as a rear track of its predecessor. Solving hundreds of differential equations numerically, where each depends on the preceding one, leads to error buildup, but with some care one can get a curve having unibike error less than 10^-7. The evidence is strong for the conjecture that the limit of the iteration exists and is a unibike curve.
format Preprint
id arxiv_https___arxiv_org_abs_2503_11847
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle A Spiral Bicycle Track that Can Be Traced by a Unicycle
Wagon, Stan
Differential Geometry
53A04
A unibike curve is a track that can be made by either a bicycle or a unicycle. More precisely, the end of a unit tangent vector at any point on a unibike curve lies on the curve (so the bike's front wheel always lies on the track made by the rear wheel). David Finn found such a curve in 2002, but it loops around itself in an extremely complicated way with many twists and self-intersections. Starting with the polar square root curve r = sqrt[t/(2 pi)] and iterating a simple construction involving a differential equation apparently leads in the limit to a unibike curve having a spiral shape. The iteration gets each curve as a rear track of its predecessor. Solving hundreds of differential equations numerically, where each depends on the preceding one, leads to error buildup, but with some care one can get a curve having unibike error less than 10^-7. The evidence is strong for the conjecture that the limit of the iteration exists and is a unibike curve.
title A Spiral Bicycle Track that Can Be Traced by a Unicycle
topic Differential Geometry
53A04
url https://arxiv.org/abs/2503.11847