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Annulus
From Latin: annulus - "small ring"
Definition: The area between two coplanar
concentric circles. A flat ring-shaped object.
Try this Drag either orange dot to resize the circles. The yellow area between them is an annulus.
(If there is no image below, see support page.)
The dimensions of an annulus are defined by the two radii R2, R1 in the figure above, which are the radii of the outer ring and the inner 'hole' respectively. The area of the annulus can be found by subtracting the area of the 'hole' from the area of the overall disk. See Area of an Annulus The adjective form is 'annular'. So for example the ring on the right could be called an 'annular plastic ring'. Other circle topicsGeneral
Angles in a circleArcs
(C) 2007 Copyright John Page
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An annulus is a flat ring shaped object, much like the throw-ring shown on the right.
One way to think of it is a circular disk with a circular hole in it.
The outer and inner circles that define the ring are