md2 Posted June 17, 2014 Share Posted June 17, 2014 diameter of sphere is 2 pi r, but from what point of view Link to comment Share on other sites More sharing options...
Acme Posted June 17, 2014 Share Posted June 17, 2014 diameter of sphere is 2 pi r, but from what point of view All. 2 Link to comment Share on other sites More sharing options...
Unity+ Posted June 17, 2014 Share Posted June 17, 2014 diameter of sphere is 2 pi r, but from what point of view I have been previewing a majority of your topics, and I got to say you aren't making sense. There is no real point of view when analyzing a shape as a whole. What are you asking specifically? Link to comment Share on other sites More sharing options...
pzkpfw Posted June 17, 2014 Share Posted June 17, 2014 All. Yes, but does md2 mean circumference? Link to comment Share on other sites More sharing options...
Acme Posted June 17, 2014 Share Posted June 17, 2014 Yes, but does md2 mean circumference? Hard to tell what md2 means, or intends for that matter. While he/she wrote 'diameter', the equation given is for the circumference of a circle and in the case of a sphere the equation is the measure of a great circle. (The diameter of a sphere is of course 2r) Nonetheless, from all [Euclidian 3-space] perspectives a circumference is a circumference, a diameter is a diameter and a great circle is a great circle. All in all I intended the brevity of my response to match the brevity of the question. A great circle, also known as an orthodrome or Riemannian circle, of a sphere is the intersection of the sphere and a plane which passes through the center point of the sphere. This partial case of a circle of a sphere is opposed to a small circle, the intersection of the sphere and a plane which does not pass through the center. Any diameter of any great circle coincides with a diameter of the sphere, and therefore all great circles have the same circumference as each other, and have the same center as the sphere. A great circle is the largest circle that can be drawn on any given sphere. Every circle in Euclidean 3-space is a great circle of exactly one sphere. ... Link to comment Share on other sites More sharing options...
pzkpfw Posted June 18, 2014 Share Posted June 18, 2014 Yep, sorry if I was too vague: I was more saying "Yes" to you (Acme) and pointing out the Circumference/Diameter thing to md2 as an aside. Whichever he meant, the crux in the OP seems to be "but from what point of view". Here, as you know, md2 seems to be getting confused that he or she drew a 3D object in 2D. The 2D representation of the 3D circumference will of course appear different depending on the point of view, but that's got nothing to do with the 3D object (and the sphere's 2r Diameter or 2.Pi.r Circumference. 1 Link to comment Share on other sites More sharing options...
Acme Posted June 18, 2014 Share Posted June 18, 2014 Yep, sorry if I was too vague: I was more saying "Yes" to you (Acme) and pointing out the Circumference/Diameter thing to md2 as an aside. Roger roger, copy copy. Whichever he meant, the crux in the OP seems to be "but from what point of view". Here, as you know, md2 seems to be getting confused that he or she drew a 3D object in 2D. The 2D representation of the 3D circumference will of course appear different depending on the point of view, but that's got nothing to do with the 3D object (and the sphere's 2r Diameter or 2.Pi.r Circumference. Roger that. We can hope md2 will return & clarify. As to 'point of view' I was trying to be ever-so-careful when I specified [Euclidean 3-space] so as to allow the possibility that some manner of manifold took on different representations. ajb? You out there? Link to comment Share on other sites More sharing options...
ajb Posted June 22, 2014 Share Posted June 22, 2014 ajb? You out there? Well I assume that he has fixed the geometry to be the standard one induced by the imbedding in 3 d Euclidean space. All the standard stuff from high school applies. The only thing that could conceivable be different is if he is talking about the topological 2-sphere, but there we don't necessarily have any notion of length. 1 Link to comment Share on other sites More sharing options...
Acme Posted June 22, 2014 Share Posted June 22, 2014 ajb? You out there? Well I assume that he has fixed the geometry to be the standard one induced by the imbedding in 3 d Euclidean space. All the standard stuff from high school applies. The only thing that could conceivable be different is if he is talking about the topological 2-sphere, but there we don't necessarily have any notion of length. I figured you would know some caveat. You da man. Link to comment Share on other sites More sharing options...
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