Definition of Terms, Continued
Cones have a generatrix that terminates in a fixed point at a vertex around
which revolves a directrix or closed curve base. The generatrix is also
known as the axis whose height is referred to as altitude.
Any point around
the cone from the base to the vertex is called an element.
A cone whose axis
is perpendicular to its base is a right cone. Planes intersecting a cone will
make the cone appear truncated or frustum. Planes intersecting a right cone
produce conic sections. Conic sections appear as curves. A conic section
perpendicular to the axis appears as a circle at the plane of intersection. A
conic section with a cutting plane oblique to the axis but making a greater
angle with the axis than the elements appears as an ellipse.
When the plane
of intersection is oblique to the axis and at the same angle to the axis as the
elements, the curves is referred to as a parabola. An oblique plane of
intersection that makes a smaller angle to the axis than the elements is known
as a hyperbola. Cones may also be used to construct helixes.
Figure 2-14 shows cones.
Figure 2-14.Cone terminology.
Continued on next page