A right conoid as a ruled surface.

In geometry, a right conoid is a ruled surface generated by a family of straight lines that all intersect perpendicularly to a fixed straight line, called the axis of the right conoid.

Using a Cartesian coordinate system in three-dimensional space, if we take the z-axis to be the axis of a right conoid, then the right conoid can be represented by the parametric equations:

${\displaystyle x=v\cos u}$

${\displaystyle y=v\sin u}$

${\displaystyle z=h(u)}$

where h(u) is some function for representing the height of the moving line.

Examples

Generation of a typical right conoid

A typical example of right conoids is given by the parametric equations

${\displaystyle x=v\cos u,y=v\sin u,z=2\sin u}$

The image on the right shows how the coplanar lines generate the right conoid.

Other right conoids include:

• Helicoid: ${\displaystyle x=v\cos u,y=v\sin u,z=cu.}$
• Whitney umbrella: ${\displaystyle x=vu,y=v,z=u^{2}.}$
• Wallis's conical edge: ${\displaystyle x=v\cos u,y=v\sin u,z=c{\sqrt {a^{2}-b^{2}\cos ^{2}u}}.}$
• Plücker's conoid: ${\displaystyle x=v\cos u,y=v\sin u,z=c\sin nu.}$
• hyperbolic paraboloid: ${\displaystyle x=v,y=u,z=uv}$ (with x-axis and y-axis as its axes).

See also

• Conoid
• Helicoid
• Whitney umbrella
• Ruled surface

External links

• "Conoid", Encyclopedia of Mathematics, EMS Press, 2001 [1994]
• Right Conoid from MathWorld.
• Plücker's conoid from MathWorld