- #1

- 31

- 1

in classical physics orbital angular momentum is defined as the cross product of the position vector 'r' and the momentum 'p'. A friend told me that all moving objects must have orbital angular momentum (even if it is moving along a straight line). That statement confuses me a lot, because mathematically the vector product can become zero.

Suppose, we fix a coordinate system and our object is moving such that the position r and the momentum p are parallel. Then, mathematically, the angular momentum is zero. But, if we shift the origin of the coordinate system, then the orbital angular momentum suddenly becomes nonzero. It seems to me, that the angular momentum depends on our choice of coordinate system. Is that right? Maybe my friend had in mind something like: We can always choose a coordinate system, such that the orbital angular momentum of a moving object is not zero. This statement somehow seems to be wrong, because I would not expect a physical property to depend on our choice of coordinate system. Can someone explain where my mistakes are?

Best wishes