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Somebody is living on a spherical world

  1. Apr 3, 2005 #1
    Somebody is living on a spherical world. He is drawing a circle of radius 1m with a rope. We know there are only 2 possible worlds.

    What is the radius of this world knowing the rope cannot circumvent the sphere ?
  2. jcsd
  3. Apr 8, 2005 #2
    which world are you exactly talking about.

    and can you please elaborate on the 2 worlds.
  4. Apr 8, 2005 #3


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    Gold Member

    The problem has insufficient information with which to define an answer.

    Well, except for a meta-answer, as in: any of an infinite number of worlds whose circumference is > 1m.
  5. Apr 8, 2005 #4
    Yes you're right : the guy tells us the perimeter of that circle of 1m radius. We know this and the fact (by another source of information) that there are only two possible worlds.
  6. Apr 8, 2005 #5
    I think I might know what kleinwolf means, but I am too lazy right now to get the answer. Here is a possible meaning to the puzzle:

    First of all, I think he means to use the rope as a kind of compass, as you might use to draw a circle on a flat piece of paper. There are two ways to do this on a sphere without breaking through the sphere. One is to stretch the rope taut around a great circle of the sphere. The other is to stretch the rope straight on the inside of the sphere. I assume (because the problem is probably solvable), that for a given length of rope, there is only one radius for the sphere that allows these two drawn circles to have the same radius. Thus, there is only one radius for the sphere that would allow the radii of the circles to be 1m.
    Last edited: Apr 8, 2005
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