Comments by "Lynott Parris" (@DenUitvreter) on "Veritasium" channel.

I understood it, and not sure that is correct, by looking at the distance covered by the centre of the circle. If you take that ribbon of the same length as the circumference, and you place that in an orbit around the big circle so the centre point of the small circle moves on it, you'll immediately understand it will not make it round because the circile that ribbon makes has the radius of the big circle plus the radius of the small circle. The length of the distance travelled by the small circle, measured by it's centre point, and the length of the distance of the 'tread' or not the same, that is where we all went wrong. The number of revolutions by the small circle is determined by the distance the centre point covers, not by the edge.... I think.
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