Right conoid

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.

A right conoid as a ruled surface.

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:

$x=v\cos u$

$y=v\sin u$

$z=h(u)$

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

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

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

Other right conoids include:

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