Definition of Terms, Continued
Circles
A circle is a closed curve in which all points along the curve are equidistant
from the center. The distance from the center point to any point along the
circle edge is called a radius (RAD or R). The distance from one side of the
circle through the center point to the opposing side of the circle is the circle
diameter (DIA).
Half of the distance around a circle is called a semicircle.
Circumference refers to the total distance around the circle. Calculate the
circumference of a circle by multiplying the diameter of the circle by 3.1416
or p (pronounced pi). A chord is a straight line joining two points on a
curve. A segment is the section of the curve cut off by the line or chord.
Quadrants result from the intersection of two radii at 90° including the
portion of the circle between the radii. Sectors are the part of the circle
bound by two radii at other than right angles including the bound portion of
the circle. Angles are formed by the intersection of radii but do not include
the bound portion of the circle. An arc is a segment of the curved portion of
the circle bound by the intersection of two radii but does not include the
radii. A straight line that intersects and passes through two points on the
circle is called a secant. Straight lines that touch but do not intersect at one
point on a circle are said to be tangent. Multiple circles sharing a common
center point are called concentric circles. Multiple circles that do not share a
common center point are referred to as eccentric circles. Eccentric circles
are most common in depicting reciprocal relationships such as in the
camshaft of an engine.
Figure 2-7 illustrates circle terminology.
Figure 2-7.—Circle terminology.
Continued on next page
2-9
