Please see diagram below showing a rigid rod mass 'm' connected at one end to a fixed frictionless pivot.

The rod swings from position A to B changing its orientation around its centre of mass.

Can anyone advise how an external torque can be formed that causes the rod to spin about its centre of mass?

enter image description here

  • 1
    $\begingroup$ The force from the pivot is not necessarily directed along the line of the rod. $\endgroup$ Aug 16, 2023 at 11:57
  • $\begingroup$ I don't think that the rod is rotating about the center of mass. the center of mass is moving a circular path about the joint due to the $~m\,g~$ $\endgroup$
    – Eli
    Aug 17, 2023 at 13:44
  • $\begingroup$ The rod has changed it's orientation in space , therefore it has some spin about its COM. Why should the contact force with the pivot not be directed along the line of the rod through its COM? $\endgroup$
    – Dubious
    Aug 24, 2023 at 22:31


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