Definition of Terms, ContinuedCirclesPoints 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 onthe convex side or outside edge of an equal or larger circle are calledepicycloid.If the circumference of a circle rolls along the concave side orinside 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.Continued on next page2-11