Definition of Terms, Continued
Circles
Points along the circumference of a circle rolling on a straight line are known
(Continued)
as cycloidal or cycloids. Points along the circumference of a circle rolling on
the convex side or outside edge of an equal or larger circle are called
epicycloid.
If the circumference of a circle rolls along the concave side or
inside edge of a larger circle, the resulting curve is a hypocycloid.
Figure 2-9 illustrates the formation of a cycloid, epicycloid, and hypocycloid.
Figure 2-9.—Cycloids, epicycloids, and hypocycloids.
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