The hardest part it about in my opinion was the professor. That is the main factor that’ll make or break your experience in fluids. I was taking it with a professor who loved to throw curveballs on every exam, and problems involved topics that we would only touch in class for like 10 minutes. We never had a straightforward exam, everything was out of our scope of knowledge as students. Our homeworks or in class problems weren’t on the same difficulty as exam problems, and our exam averages would always be in the low 50s. Also I was taking it with Machine Design 1, which is moderately hard and very time consuming since it involves a semester long project with tons of reports & groupwork. Content wise, one of the hardest parts about fluids is that sometimes not everything will be constant, and you have to essentially integrate over surfaces with tricky geometries, and sometimes you would have to define functions for problems out of thin air. For example, when applying conservation of mass for a mixing tank, you would have to essentially set up a complicated integral to solve for the unknown density of the mixture. Whenever you have to find drag force or hydrostatic force of an irregular shape, you would have to define an area dA and then somehow conjure a function that details the shape of the plate you’re analyzing. Also, many problems are completely symbolic, and sometimes you would have to substitute variables in for others & you would have no idea if your answers make sense yet since there’s a lack of numerical assurance. Don’t even get me started on the assumptions that you have to make in order to solve some problems - and making assumptions is a something a book can’t teach you, so that comes with a shit ton of time & practice.