# I Can angular momentum be applied to non circular rotations?

1. Dec 2, 2017

### Fruit Water

One of the reasons I've been so stumped about learning about angular momentum in QM, is that in my classical physics class we only applied it to circular motions. Hence, while I am aware that angular momentum is connected to spherical harmonics, the orbital shapes (besides s) isn't really circular motion to me. Can someone clarify this for me?

2. Dec 2, 2017

### PeroK

In classical physics, angular momentum applies to all motion. A partial moving in a straight line has non-zero angular momentum about any point not on that line.

Conservation of linear momentum can be seen as a special case of conservation of angular momentum.

In QM particles do not have defined trajectories such as a circular orbit. The spherical harmonics represent a probability density distribution, not a trajectory.

3. Dec 2, 2017

### gr71cj5

They taught you using a circle since it is the easiest to visualize and grasp the concepts. Just like in entry level physics when they have you calculate aspects of a ball rolling down an incline they do not include atmospheric resistance, surface frictions between the two items, or atomic attraction/repulsion characteristics of the materials. What PeroK stated is spot on, however, to reiterate from a different angle (hehe) think of the vectors of force at play when an object is in motion. If only one vector, no angular momentum, if two or more vectors, there is angular momentum. The path (circle or not) is not a determining factor in if there is angular momentum.