You should use the Udemy Marketplace Insights tool to help you determine if that topic is worth your time. General Physics courses are in high-demand, but there's also a lot of competition; the average physics course earns $16/month.
When I searched for dynamics, the average course earns around $24/month. In general,sSpecialized "niche" courses, that aren't in high-demand generally don't do as well as general broader courses, such as an AP Physics course.
When using the tool, look at both demand as well as competition. And also, don't only use the tool, but do some research on Udemy yourself, looking at the competition to see what you're up against.