I've been working on my SR book http://www.lightandmatter.com/sr/ and its presentation of a suite of related mathematical tools such as the Levi-Civita tensor. This is aimed at the upper-division undergraduate level, although there are optional sections at the end of some of the chapters that go into topics that would normally be seen in a graduate course. Currently I have a treatment of the Levi-Civita tensor and volume forms in an optional section at the end of ch. 7. Ch. 8 is on rotation and currently makes no mention of angular momentum. I would like to add a section on angular momentum and make some use of the tools previously developed in ch. 7. At this stage the reader does not yet know about the stress-energy tensor, which is discussed in ch 9. Does anyone know of an interesting, simple, concrete, real-world application of relativistic angular momentum that can be done with these tools? When I think of relativistic objects that have angular momentum, I think of neutron stars, nuclei, hadrons, and atoms. Examples involving neutron stars seem not doable at this stage because they involve gravity, and this is an SR book. Nuclei, hadrons, and atoms seem like they would lead too far into quantum mechanics, which I don't assume my readers know much about beyond what's described in a freshman survey course. Any suggestions? Maybe there would be something interesting from relativistic heavy ion physics? Or small corrections in high-precision experiments, such as tests of Lorentz invariance?