String around the Earth: excellent math question

Have you ever considered snugly wrapping a string around the entire Earth? If you did that, and then you added merely one additional meter of string (which would then raise the string uniformly off the surface of the Earth), how much higher off the ground would that new string be (the original long string, plus one additional meter)? Here’s a simple statement of the problem, allegedly first used by Ludwig Wittgenstein.

Here the math. Wonderful problem and surprising solution.

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Erich Vieth

Erich Vieth is an attorney focusing on civil rights (including First Amendment), consumer law litigation and appellate practice. At this website often writes about censorship, corporate news media corruption and cognitive science. He is also a working musician, artist and a writer, having founded Dangerous Intersection in 2006. Erich lives in St. Louis, Missouri with his two daughters.

This Post Has 4 Comments

  1. Avatar of Planeten Paultje
    Planeten Paultje

    Reduce R to 0 and you have your basic circle with the circumference of 1m. Funny stuff this ;-).

    1. Avatar of Erich Vieth
      Erich Vieth

      Planeten: I did the same thing; the one meter circumference has the same radius as the Delta r based on any other size sphere. It surprised me that you get the same delta r, no matter how big the starting size of the sphere.

  2. Avatar of Dan Klarmann
    Dan Klarmann

    My first impression is that

    r = C/(2 x π).

    But I also know pre-calculus, so

    Δr = ΔC/(2 x π)

    So every Δ one adds to the circumference obviously adds 0.159 x Δ to the radius.

    No need to work out the two separate answers.

    Many counter-intuitive things become intuitive, once you know some math.

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