Torque from a frame of reference

[SDewan]

Whenever we define torque from a frame of reference, is it necessary for the frame to be inertial?
Please explain because I am unclear on this.

 

[BvU]

Yes. In e.g. an accelerating frame of reference you no longer have $\vec \tau = I\vec\alpha$.
Example: you sit in an accelerating car and have to lean forward to stay sitting upright. $\alpha$ of your head w.r.t. your hips is zero but you (or the backrest) do have to exercise a torque to stay with your head above your hips.

 

[SDewan]

In case of non inertial frame, a pseudo force should be taken and then we can proceed writing the torque. Right?