ProTeacher Community - View Single Post - Number of Faces for Cone and Cylinder?
View Single Post

High School Math Teacher
Old 06-09-2009, 12:46 PM
Clip to ScrapBook #14

I think it is wonderful that 4th grade teachers are discussing these concepts with each other!

However, in high school geometry we use the words faces, edges, and vertices for polyhedra only. Polyhedra are 3-dimensional shapes composed of polygonal regions, any two of which have at most a common side. (Just a fancy way to say only things like prisms and pyramids.)

I agree that a circle is the limit as the number of sides of a polygon increases to an infinitely large number. If you continue down this road...not only would the bases of a cylinder be "faces", but the cylinder would have inifinitely many rectangles in its lateral surface area, and the cone would have infinitely many triangles in its surface area.

It looks like we may be confusing some of our students. So, in HS geometry, we refer to the 2 bases of a cylinder and the 1 base of a cone. Neither the cone, nor the cylinder, (or for that matter, a sphere) is considered to have edges or faces (as they are defined in geometry).
  Reply With Quote

Copyright © ProTeacher®
For individual use only. Do not copy, reproduce or transmit.