Tractrix

Cartesian equation: x = 1/cosh(t), y = t - tanh(t)

Click below to see one of the Associated curves.

Definitions of the Associated curves

Evolute       Involute 1       Involute 2

 Inverse curve wrt origin      Inverse wrt another circle

Pedal curve wrt origin      Pedal wrt another point

Negative pedal curve wrt origin      Negative pedal wrt another point

   Caustic wrt horizontal rays      Caustic curve wrt another point

The tractrix is sometimes called a tractory or equitangential curve. It was first studied by Huygens in 1692 who gave it its name. Later Leibniz, Johann Bernoulli and others studied the curve.

The study of the tractrix started with the following problem being posed to Leibniz:

What is the path of an object dragged along a horizontal plane by a string of constant length when the end of the string not joined to the object moves along a straight line in the plane?

He solved this using the fact that the axis is an asymptote to the tractrix.

The evolute of a tractrix is a catenary. Among the properties of the tractrix are the fact that the length of a tangent from its point of contact to an asymptote is constant. The area between the tractrix and its asymptote is finite.

When a tractrix is rotated around its asymptote then a pseudosphere results. This is a surface of constant negative curvature and was used by Beltrami in 1868 in his concrete realisation of non-euclidean geometry.
You can see this Welcome page Famous curves index
Previous curve (Famous curves) Next curve
Biographical Index Chronologies History Topics Index Birthplace Map Mathematicians of the day Anniversaries for the year Search Form Simple Search Form Search Suggestions


JOC/EFR February 1996