@johnmdudley Usage is inconsistent in my experience. I think I would tend to treat "dynamics" as plural when it stands alone as a noun (e.g. "the dynamics are nonlinear") but generally singular when referring to a type of dynamics in a noun phrase (e.g. "nonlinear dynamics is a well-studied phenomenon").

If one is publishing in a specific journal, it may pay to check the style guide for that journal. I was curious what a general dictionary would say and see Merriam-Webster says "plural in form but singular or plural in construction".