• FrankTheHealer@lemmy.world
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    11 months ago

    So I’m confused. I saw this and initially thought it was just a matter of circumference. Suppose the radius of circle A is 10 and the radius of circle B is twice that amount, so it’s 20

    The formula to find the circumference of a circle is C = 2πr

    So for circle A;

    2π10 = 62.831

    And for circle B;

    2π20 = 125.663

    Then to find the difference in circumferences, divide them

    125.663/62.831 = 2.000

    Therefore, it should take two rotations to rotate one circle around the other

    What am I getting wrong here?

    • CommationCerebrole@jlai.lu
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      11 months ago

      There’s one extra-rotation from an external perspective due to the revolution of one around the other. So the formula is r1 / r2 + 1.

      This extra-rotation doesn’t appear from the point of view of the circles, or if you consider the circles as two stationary gears