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Say that I have two magnetic dipoles, one of which is rigidly attached to a freely movable inflexible body at some point that is not at the body's center of mass, while the other is fixed in space. Now I already know how to compute both the force and torque that the dipoles exert directly upon eachother per the wikipedia article on magnetic dipoles, and I can calculate the net force and torque that is exerted on the body due to said force between them, per the answer to Force applied off-center of an object, but the answer to that question does not address how to also calculate any additional force and torque on the body due to any torque that is exerted on an off-center point.

This question is admittedly highly similar to Force applied off-center of an object, but I do not believe it is identical. They differ in that the other question was asking about computing effective torque and force on the center of mass from a force being applied off-center, while I am asking about applying both force and torque through an off-center point, and computing the effective force and torque on the center of mass from that. As I said, I already am aware of how to calculate the net force and torque on the rigid body due to just the force that exists between the two points, but how do add in the issue of torque between them?

Edit:

This is for 3d.

Although I know that torque does not any any additional force when applied to the object's center of mass. If I twist an object around a point that is not at the object's center, however, in addition to the object starting to spin, the object's center of mass will be moved, and it will spin as if a force and torque HAD been applied to the object's center of mass. What is that force and torque?

Edit: I do not understand how this question is answered by the one that has been alleged to already answer it, nor do I understand what anyone is thinking I was actually asking about to suggest that the answer to that question would answer mine. They seem entirely different to me.

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  • $\begingroup$ A torque does not impose any additional forces. If you have multiple forces then you need to sum them up to get the motion of the center of mass. You also need the net torques (including the effects of force at a distance). $\endgroup$ – John Alexiou Nov 21 '14 at 20:10
  • $\begingroup$ Is this 2D or 3D? $\endgroup$ – John Alexiou Nov 21 '14 at 20:11
  • $\begingroup$ If you apply a pure torque on a (resting) rigid body the center of mass will not move. The body will rotate about the center of mass. Albeit, it is very hard to apply a pure torque (without a net force component). See physics.stackexchange.com/a/81078/392 $\endgroup$ – John Alexiou Nov 21 '14 at 20:47
  • $\begingroup$ I am applying torque on the dipole that is attached to the rigid body, which I know by itself would not cause the dipole to move, but the torque will want to make the dipole spin. Because the dipole is not allowed to spin relative to the body, however, wouldn't that torque have to get transferred to the rigid body it is attached to in some way? $\endgroup$ – Mark Nov 21 '14 at 23:54
  • $\begingroup$ I do not understand how the answer to the question this is alleged to answer this question accomplishes that. I see nothing in the other question about how to derive effective force upon the center of mass from a torque issued at a point that was not at the center of mass. $\endgroup$ – Mark Dec 3 '14 at 19:24