Imagine a tube, split in half laterally, discarding one of the halves. Does the remaining shape have a name? Like this.

  • 4
    $\begingroup$ Like a half pipe? I'd just say half pipe. $\endgroup$ – Jackozee Hakkiuz May 15 at 2:18
  • 1
    $\begingroup$ I'd call it a disk. $\endgroup$ – Couchy311 May 15 at 2:28
  • 1
    $\begingroup$ It can be called a circular trough. $\endgroup$ – John Douma May 15 at 2:45
  • 5
    $\begingroup$ @Couchy311 >implying we allow equivalence under ambient isotopy. Then the homotopy theorist comes and calls it a point smh. $\endgroup$ – Jackozee Hakkiuz May 15 at 2:46
  • $\begingroup$ Are you referring to something like this? I'd like to know as well. $\endgroup$ – ExtremeRaider May 15 at 3:00

I don't have a formal name for it but circle with a smaller circle cut out of it is an "annulus". Extruding a shape into 3d with a rectangle makes it a prism so the full shape would be "annula-prism" and a half version of the shape would be a "semi-annula-prism".

If the tube is round rather then rectangular (so it looks like a donut) it is a half-torus.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.