Orbital Angular Momentum: Need at least 2 particles?

[LarryS]

The definition of orbital angular momentum, whether for classical mechanics or for quantum mechanical operators, is rxp. Technically, according to this definition, one particle can possesses orbital angular momentum - in this case about the origin.

But I cannot think of any examples, in classical or quantum mechanics, in nature in which a system of one particle has orbital angular momentum. It seems like a minimum of 2 "particles" is necessary.

Comments?

As always, thanks in advance.

 

[mfb]

Every system of one particle has "orbital" angular momentum - in some frames.
It's just pointless to consider those reference frames if you really just have one particle. It is much more convenient to put the origin of your reference frame where the particle is.

 

[LarryS]

Every system of one particle has "orbital" angular momentum - in some frames.
It's just pointless to consider those reference frames if you really just have one particle. It is much more convenient to put the origin of your reference frame where the particle is.

Makes sense. If one has a system of just 1 particle, then you can make the system's angular momentum "go away" by moving the origin of the reference frame to the position of the particle. But, obviously, you cannot do that if the system contains 2 or more particles. It's like those system's angular momentum are "absolute".