Definition of Terms, ContinuedCirclesA circle is a closed curve in which all points along the curve are equidistantfrom the center. The distance from the center point to any point along thecircle edge is called a radius (RAD or R). The distance from one side of thecircle through the center point to the opposing side of the circle is the circlediameter (DIA).Half of the distance around a circle is called a semicircle.Circumference refers to the total distance around the circle. Calculate thecircumference of a circle by multiplying the diameter of the circle by 3.1416or p (pronounced pi). A chord is a straight line joining two points on acurve. 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 theportion of the circle between the radii. Sectors are the part of the circlebound by two radii at other than right angles including the bound portion ofthe circle. Angles are formed by the intersection of radii but do not includethe bound portion of the circle. An arc is a segment of the curved portion ofthe circle bound by the intersection of two radii but does not include theradii. A straight line that intersects and passes through two points on thecircle is called a secant. Straight lines that touch but do not intersect at onepoint on a circle are said to be tangent. Multiple circles sharing a commoncenter point are called concentric circles. Multiple circles that do not share acommon center point are referred to as eccentric circles. Eccentric circlesare most common in depicting reciprocal relationships such as in thecamshaft of an engine.Figure 2-7 illustrates circle terminology.Figure 2-7.—Circle terminology.Continued on next page2-9

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