Pronunciation: /ˈæn.jə.ləs/ Explain

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What is the difference between an annulus and a circle?
Manipulative 1 - Annulus Created with GeoGebra.

An annulus is the region between two concentric circles.[2] The area of the annulus is the difference between the areas of the circles: A = π(r12 - r22) where r1 > r2.

Check box Understanding Check

What is the area of an annulus with an inner radius of 1m and an outer radius of 3m?

Click here for the answer.

Examples of Annulus

Figure 2: Roll of paper towels
Figure 3: Roll of pipe tape
Figure 4: Pipe. The cross section of a pipe is an annulus.


1. A pipe has an inner radius of 3 cm. It has an outer radius of 3.5 cm. It is 100 cm long. What is the total volume of the pipe, not including the empty space inside?

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Click here for the answer.

2. The same pipe is made of a metal alloy with a density of 3g/cm3. What is the mass of the pipe in challenge 1?

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  1. McAdams, David E.. All Math Words Dictionary, annulus. 2nd Classroom edition 20150108-4799968. pg 17. Life is a Story Problem LLC. January 8, 2015. Buy the book
  2. Stöcker, K.H.. The Elements of Constructive Geometry, Inductively Presented. pp 44-45. Translated by Noetling, William A.M, C.E.. Silver, Burdett & Company. 1897. Last Accessed 6/12/2018. Buy the book

More Information

  • Annulus. Math Is Fun. 6/19/2018.

Cite this article as:

McAdams, David E. Annulus. 4/11/2019. All Math Words Encyclopedia. Life is a Story Problem LLC.

Image Credits

Revision History

4/11/2019: Changed equations and expressions to new format. (McAdams, David E.)
1/12/2019: Replaced pipe image and paper towel image, and tape image. (McAdams, David E.)
12/21/2018: Reviewed and corrected IPA pronunication. (McAdams, David E.)
6/14/2018: Removed broken links, changed Geogebra links to work with Geogebra 5, updated license, implemented new markup. (McAdams, David E.)
12/27/2009: Added "Reference" and "More Information". (McAdams, David E.)
12/19/2008: Changed figure 1 to a manipulative. (McAdams, David E.)
6/23/2008: Reorganized content, added challenge and understanding check. (McAdams, David E.)
4/18/2008: Added illustrations. (McAdams, David E.)
4/17/2008: Initial version. (McAdams, David E.)

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