A point on a rolling circle traces out the curved path from the first animation.

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1. Robert McNees (mcnees@mastodon.social)'s status on Monday, 29-Jan-2024 18:18:23 UTC Robert McNees

   in reply to

   What does it mean that a brachistochrone is "part of a cycloid?”

   A cycloid is the path traced out by a point on the rim of a rolling circle. Here's how a cycloid gives the brachistochrone from the first tweet.