Definition of Terms, ContinuedSolids(Continued)Cones have a generatrix that terminates in a fixed point at a vertex aroundwhich revolves a directrix or closed curve base. The generatrix is alsoknown as the axis whose height is referred to as altitude.Any point aroundthe cone from the base to the vertex is called an element.A cone whose axisis perpendicular to its base is a right cone. Planes intersecting a cone willmake the cone appear truncated or frustum. Planes intersecting a right coneproduce conic sections. Conic sections appear as curves. A conic sectionperpendicular to the axis appears as a circle at the plane of intersection. Aconic section with a cutting plane oblique to the axis but making a greaterangle with the axis than the elements appears as an ellipse.When the planeof intersection is oblique to the axis and at the same angle to the axis as theelements, the curves is referred to as a parabola. An oblique plane ofintersection that makes a smaller angle to the axis than the elements is knownas a hyperbola. Cones may also be used to construct helixes.Figure 2-14 shows cones.Figure 2-14.—Cone terminology.Continued on next page2-16

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