What makes a door move, the torque or the force or both?

[sreerajt]

May be a relevant read:
Leo Rausér's answer to Why exactly is it scientifically impossible to lift someone up by the neck? How strong do you have to be to do so? - Quora

 

[sophiecentaur]

If there is a net force, the torque depends on the choice of reference axis. That choice is free.

I may have just confused myself. If you have a reaction wheel system, attached to a free object, that cannot apply any net force - or you would have a reaction less drive à la Eric Laithwaite. Ah - but attaching a hinge provides another reaction torque in addition to that, due to the MI of the door.

 

[jbriggs444]

I may have just confused myself. If you have a reaction wheel system, attached to a free object, that cannot apply any net force - or you would have a reaction less drive à la Eric Laithwaite. Ah - but attaching a hinge provides another reaction torque in addition to that, due to the MI of the door.

The scenario I have in mind is a door with the hinge pins pulled out, just barely stuck in the jamb (*). You pull on the knob. The door comes out of the doorway, rotating as it does so. But if your choice of reference axis is at the knob then there was no torque and no change in angular momentum. Nonetheless, the door is unambiguously changing its orientation -- it is rotating without a torque having been applied.

The counter-balancing angular momentum is, of course, accounted for by the linear motion of the door's center of mass.

(*) Assume that you've also trimmed away the wood in the door frame so that the hinge-ward 1/3 of the door width is free to push into the jamb without impediment.