Maybe some rudimental tensor calculus? Our electrodynamics course was based on Landau&Lifshitz.
First google result: link. This is fairly sufficient and not much for an undergraduate level course.
Lets say we have a weight attached to a spring. When releasing it under water (whole motion occours under water) at different initial amplitudes, will logarithmic decrement be the same? And will the period change?
I think it should be the same for different initial amplitudes. But...