In AP Physics 2, we whiteboarded the fluid dynamics problems today. This went better in that the questions and discussions were richer than when we whiteboarded the fluid statics problems last week. I expect this was due to two factors: one, students were better prepared; two, the problems were more challenging. In one class, we had a great discussion about why the pressure in an unconstrained stream must be atmospheric pressure. In another, we had a good discussion about how reasoning through a problem conceptually can provide bounds on possible answers that can be used to evaluate the reasonableness of the calculated answer.