Hello. My first post here. I'm having trouble with the basics of rigid body rotation. I have a few questions (my apologies if they are too childish; I'm very new to this): 1) Is torque (and other angular parameters like angular velocity, angular acceleration etc.) defined about a point or an axis? If about an axis, then can we choose any point on the axis as origin when calculating r x f? 2) Is a couple always required to produce rotation? If so, then how can torque be produced with just one force? If we have a rod (no gravity, no friction) and we apply force at one of its end, then will it start rotating? The force will produce torque about all the points on the rod except the end, but there will be no couple. 3) In rotational equilibrium, does the net torque about every point/axis have to be zero? Is this even possible? I mean, any force will produce torque about some point. Thanks in advance to anyone who can help me out. Edit: I think I've posted in the wrong section. How do I move/delete this thread?