Understanding Rigid Body Rotation: Principles and Observations

[Tian En]

Just to confirm a few points:

1. A body frame rotates with a body. It need not be aligned to the rotation axis.
2. Angular momentum vector always aligned with rotation axis (not deviates from it).
3. An observer on the body surface (body frame) observes no motion on a body.
4. Principal axis of rotation comes from the symmetry of the body.
5. Principal axis of rotation need not be rotation axis itself.

For point 3, is there a body angular velocity vector in the first place as observed by the observer in the body frame? I think if the observer is in the external static frame, he can then observe the body precesses and hence the existence of angular momentum vector.

Thanks.

 

[Gigaz]

An observer can always determine the rotation of his coordinate system from the Coriolis force.

 

[Dr.D]

Principal axis of rotation comes from the symmetry of the body.

There exists principal coordinates even when there is no evident symmetry.

 

[Tian En]

Is angular momentum vector of the rotating body precessing in the frame of an observer in the rotating body?