My question is how to prove that if you measure the angular momentum of an object that only has spin angular momentum (only spins around its center of mass), the answer is independent of the origin you chose. I.e., what Walter Lewin says in this lecture: http://ocw.mit.edu/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/video-lectures/lecture-20/ at 15:59 Thanks in advance!

Question

My question is how to prove that if you measure the angular momentum of an object that only has spin angular momentum (only spins around its center of mass), the answer is independent of the origin you chose. I.e., what Walter Lewin says in this lecture:  http://ocw.mit.edu/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/video-lectures/lecture-20/  at 15:59 Thanks   in advance!

vincent-lyon.fr · Answer

Linear momentum and angular momentum form a screw.
If C is the centre of mass and A any point, you have:

$\vec L(A)=\vec L(C)+\vec{AG}\times\vec p$

If the centre of mass is fixed in your frame of reference, then $\vec p=m\,\vec v(C)=\vec0$, so this proves that whatever the point A you chose, $\vec L(A)=\vec L(C)$

anonymous · Answer

Ah Ok thanks!, but what is G on the equation? And what does it means they form a screw

vincent-lyon.fr · Answer

Sorry, I meant $\vec{AC}$, G is how you denote centre of mass in my country. Screw: http://en.wikipedia.org/wiki/Screw_theory