Minimum Radius Cylinder for Tangent Line-Contact with Cone

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Discussion Overview

The discussion revolves around determining the minimum radius of a cylinder that can maintain line contact with a 45° right-angle cone placed on a table. The focus is on the geometric relationship between the cone and the cylinder, exploring the conditions under which they can be tangent without intersection.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant describes the scenario of a cone on a table, questioning the minimum radius of a cylinder that can maintain line contact with the cone's surface.
  • Another participant seeks clarification on whether the 45° angle refers to the sides of the cone or the angle at the apex.
  • A participant expresses confusion, suggesting that a cylinder could maintain line contact regardless of its diameter, questioning the problem's premise.
  • One participant proposes that the problem involves finding the dimensions of an ellipse formed by viewing the cone from the table's surface and then determining the radius of a circle that circumscribes this ellipse.
  • A later reply confirms the understanding of wrapping the table around the cone and seeks existing equations or methods to derive the minimum radius.

Areas of Agreement / Disagreement

Participants express differing interpretations of the problem, particularly regarding the conditions for line contact and the geometric implications. There is no consensus on the approach or the specific equations needed to solve the problem.

Contextual Notes

Participants have not resolved assumptions about the definitions of angles or the geometric configurations involved. The discussion includes varying interpretations of how the cone and cylinder interact.

Who May Find This Useful

Readers interested in geometric relationships, tangential contact problems, or those exploring mathematical modeling of physical objects may find this discussion relevant.

gwiz
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If I have a 45° right-angle cone and I place it on a table on the conical surface (not the base), there should be a line-contact along the cone (the table is tangent to the conical surface). The table can be seen as a cylinder with an infinite radius, so, my question is, what is the minimum radius cylinder that the cone can lie in, while maintaining the line-contact (remaining tangent)?
 
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Does 45° refer to the angle the sides of the cone make with the base, or the maximum angle formed by the "nose" of the cone?
 
I don't understand.

I mean, when you place a cylinder on its side on top of a table, it also has line contact, no matter what the diameter of the cylinder is...to that end, a cone and a cylinder could have line contact, no matter what the radius of either of them.

did I misunderstood the problem? or what?
 
I believe what he is asking is: if you were able to roll up the surface of the table to form a cylinder around the cone without disturbing the way the cone is lying on the table and without intersecting any part of the cone, what is the minimum radius of such a cylinder?
 
So, the problem then becomes...

Find the dimensions of the ellipse formed when viewing the "tilted" cone from the surface of the table. Then, find the dimensions of a circle that will circumscribe the ellipse, intersecting at only one point: the "bottom" of the ellipse, which lies at one end of the minor axis.
 
Oh, I see...after reading the posting I had forgotten about the title...the wrapping of the table onto a cylinder enclosing the cone!...I wrapped the table in the other direction so my cone was left outside the cylinder.

I get it now.
 
Yes, that is exactly right. I am wrapping the table around the cone, and trying to find the minimum radius that remains tangent to the line contact of the cone. Does anyone know of any existing equations for that, or do I just need to drudge through it, and derive it?
 

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