epitrochoid

[ep-i-troh-koid]

Geometry.

1. a plane curve generated by the motion of a fixed point on the radius or extension of the radius of a circle that rolls externally, without slipping, on a fixed circle. The epitrochoid is a generalization of the epicycloid.

Word History and Origins

Origin of epitrochoid¹

First recorded in 1835–45; epi- + trochoid

Example Sentences

The locus of any other carried point is an “epitrochoid” when the circle rolls externally, and a “hypotrochoid” when the circle rolls internally.

From Project Gutenberg

In the headquarters of Detroit's automakers, executive desk tops and coffee tables have lately sprouted plastic models of a strange-looking engine, and in high-level conversations around them, knowing mentions are made of something called an epitrochoid.

From Time Magazine Archive

Visitors soon learn that the models are see-through likenesses of the Wankel rotary engine�and an epitrochoid, in case they did not know, is the bloated figure-eight shape that its rotor follows when moving.

From Time Magazine Archive

In either instrument, the semi-major axis C X is equal to S R, and the semi-minor axis to S P. The ellipse, then, is described by these arrangements because it is a special form of the epitrochoid; and various other epitrochoids may be traced with Suardi's pen by substituting other wheels, with different numbers of teeth, for a in Fig.

From Project Gutenberg