# What would these shapes be called? **URL:** \ **Category:** Factual Questions\ **Created:** [November 22, 2003, 4:25pm UTC](https://boards.straightdope.com/t/what-would-these-shapes-be-called/214693 "2003-11-22T16:25:54Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![gypsymoth3](https://avatars.discourse-cdn.com/v4/letter/g/85e7bf/32.png) [@gypsymoth3](https://boards.straightdope.com/u/gypsymoth3)\ **Post date:** [November 22, 2003, 4:25pm UTC](https://boards.straightdope.com/t/what-would-these-shapes-be-called/214693/1 "2003-11-22T16:25:54Z")
i’m doing geometry this year, and we’ve pretty much gotten out of all the polyhedron crap for now. but i was wondering about 2 shapes my geometry teacher cannot identify. 1. if you take a right circular cone, and stretch the base to an oval rather than a circle, and then stretch the vertex into a line segment rather than a point, what shape do you get? 2. have you ever seen one of those weird popsicles in a paper pouch? okay, this one is a little harder to describe. if you take a cube and flatten the top face into a line segment from left to right, you’ll get a triangular prism. but when you flatten the base of the prism into a line prependicular to the line segment opposite the base, what do you get, specifically? i think this one is some kind of tetrahedron with 4 tirangular faces, but is there a specific name for it? ---
**Author:** ![wolf\_meister](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolf_meister/32/15202_2.png) [@wolf\_meister](https://boards.straightdope.com/u/wolf_meister)\ **Post date:** [November 22, 2003, 4:53pm UTC](https://boards.straightdope.com/t/what-would-these-shapes-be-called/214693/2 "2003-11-22T16:53:31Z")
For Shape #2 how about a right regular pyramid? [http://www.1728.com/volpyrmd.htm](http://www.1728.com/volpyrmd.htm) (Scroll down for the diagram). That’s my site by the way (with LOTS of other diagrams and calculators) ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [November 22, 2003, 5:02pm UTC](https://boards.straightdope.com/t/what-would-these-shapes-be-called/214693/3 "2003-11-22T17:02:18Z")
If I follow your instructions correctly, the latter is exactly a tetrahedron (four triangular faces). See the picture on this page: [http://mathworld.wolfram.com/Tetrahedron.html](http://mathworld.wolfram.com/Tetrahedron.html) > [@](#): > > There are no other convex polyhedra other than the tetrahedron having four faces. ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [November 22, 2003, 5:18pm UTC](https://boards.straightdope.com/t/what-would-these-shapes-be-called/214693/4 "2003-11-22T17:18:33Z")
#2 is a tetrahedron with four isosceles triangles for faces. These will necessarily be congruent. It does qualify as an [Isosceles Tetrahedron](http://mathworld.wolfram.com/IsoscelesTetrahedron.html). However, not all Isosceles Tetrahedra are of this form. ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [November 22, 2003, 7:10pm UTC](https://boards.straightdope.com/t/what-would-these-shapes-be-called/214693/5 "2003-11-22T19:10:02Z")
> [@](#): > > \*Originally posted by Achernar \* > #2 is a tetrahedron with four isosceles triangles for faces. These will necessarily be congruent. I’m sorry, I realize now this is not true. The OP describes a tetrahedron with four congruent isosceles triangles for faces. But I was wrong; not all tetrahedra with four isosceles faces will have all faces congruent. The OP’s shape is what you’d get if you took a regular tetrahedron, held two vertices between your thumb and forefinger of one hand, held the other two vertices between your thumb and forefinger of your other hand, and pulled. ---
**Author:** ![radar\_ralf](https://avatars.discourse-cdn.com/v4/letter/r/b2d939/32.png) [@radar\_ralf](https://boards.straightdope.com/u/radar_ralf)\ **Post date:** [November 22, 2003, 9:26pm UTC](https://boards.straightdope.com/t/what-would-these-shapes-be-called/214693/6 "2003-11-22T21:26:05Z")
[slight\_hijack] **wolf\_meister** , have you heard of a new term being used? It is “conamyds” and is used to describe what I think is properly termed a truncated cone; in other words, a cone with the tip cut off. Nice website, BTW.[/slight\_hijack] ---
**Author:** ![wolf\_meister](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolf_meister/32/15202_2.png) [@wolf\_meister](https://boards.straightdope.com/u/wolf_meister)\ **Post date:** [November 23, 2003, 6:49pm UTC](https://boards.straightdope.com/t/what-would-these-shapes-be-called/214693/7 "2003-11-23T18:49:49Z")
**radar ralf** Is a conamyd the new term for a frustum? [http://www.1728.com/volcone.htm](http://www.1728.com/volcone.htm) Thanks for the postive review on my website.