Roulette (curve)

In the differential geometry of curves, a roulette is the general concept behind cycloids, epicycloids, hypocycloids, and involutes. Take two curves. Fix some point, called the generator or pole, in relation to the first curve. Roll the first curve along the second; the generator traces out a curve. Such a curve is called a roulette. Working on the complex plane, let r and f be parametrisations of curves such that for all t. The roulette of p as r is rolled on f is then\n: Roulettes in higher spaces can certainly be imagined but one needs to align more than just the tangents.

Example

\nFixed curve is a catenary, rolling curve is a line:\n:   \n:   \n:\nif p=-i the expression is real and the roulette is a horizontal line. In other words, a square wheel could run without bouncing in a road that was a matched series of catenary arcs.

External links

\n*Mathworld page on roulettes Category:Geometry\n It needs pix!