The involute of a circle is a
Spiral . In
Cartesian Coordinates the curve follows:
Where: ''t'' is the angle and ''a'' the
Radius
The involute of a catenary through its
Vertex is a
Tractrix . In
Cartesian Coordinates the curve follows:
Where: ''t'' is the angle and
Sech is the hyperbolic secant (1/cosh(x))
''
With
we have
and
substitute
to get
One involute of a cycloid is a
Congruent cycloid. In
Cartesian Coordinates the curve follows:
Where ''t'' is the angle and ''a'' the
Radius
The
Involute of a circle has a property that makes it important to the
Gear industry: if the teeth of two mating gears have the shape of an involute, their relative rates of rotation are constant while the teeth are engaged. With teeth of other shapes, the relative speeds rise and fall as successive teeth engage, resulting in vibration, noise, and excessive wear. For this reason, nearly all modern gear teeth bear the involute shape.