Rotation of a non pivot object

[VHAHAHA]

my teacher told.me.that If a rotating uniform stick is falling, the axis of rotation is about the cm of the stick.
I don't understand why it is about the cm of the ball. I have searched on google and i found no answer.
Can anyone give me some reference so that I can read? Can anyone explain to me? Thank you

 

[UltrafastPED]

Try this: http://ocw.mit.edu/courses/physics/8-01sc-physics-i-classical-mechanics-fall-2010/rotation-and-translation/two-dimensional-rotation-and-translation-dynamics/MIT8_01SC_coursenotes27.pdf

 

[VHAHAHA]

i have read this note
but i still can't the answer
any tips?

 

[D H]

You can describe the motion of a rigid body as a combination of translation of some point fixed with respect to the rigid body and rotation about that point. That point? It's completely arbitrary. It doesn't even have to be a point on the object. It's a consequence of Euler's rotation theorem.

So why choose the center of mass? That is the one point for which translational and rotational motion decouple from one another.