1. The problem statement, all variables and given/known data The latex document for these equations wasnt updating correctly, so Ive included them as an attachment whereever there is a ... in the text Ok, Im trying to understand the Reynolds transport theorem, but i dont understand part of it. 2. Relevant equations This is the actual equation Im specifically interested in: ... 3. The attempt at a solution Now I know one term would be just the chain rule for f(phi) ... , but Im not sure how the derivative works for the other term to lower the order to a surface derivative. From texts I found, I guess the answer should be something like, ... but I dont really understand how to explicity take the derivative of the integral to lower the order.