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Showing content with the highest reputation on 01/19/2019 in all areas

  1. 1 point
    Judging from the recent thread “Where are you?” some people here are interested in spherical geometry, so you might be interested in a curious fact about space discovered by the English theoretical physicist P.A.M. Dirac (1902-1984) – specifically the “space” of rotations in three dimensional space. At the bottom of the following webpage you’ll find a link to a computer program (Windows) that generates movies illustrating his discovery in various ways: How a Spinning Object Can Remain Connected to a Stationary One It can also show a movie that illustrates the principle behind the spinning jenny used to twist fiber into thread.
  2. 1 point
    The pins are rigidly affixed to the rod. They cannot slide along the rod, nor can it slide through them. The crayon is held by a cylinder welded to the end of the rod. One pin is closer to the crayon than the other. The pins are mounted to the sleds via the sleds’ collars. The pins are limited to rotating in the collars on their vertical axes. Grooves X and Y are perpendicular to each other. Sled 1 is limited to sliding in groove X, and sled 2 is limited to sliding in groove Y. The crayon is in constant contact with the surface beneath its tip. When horizontal force is applied to the crayon’s holding cylinder, perpendicular to the rod, what shape will be created by the crayon’s path once it has completed a full cycle?