We added two more assumptions to our ideal fluid model: irrotational and non-viscous This allows to focus on only a few forms of energy with fluids, and these assumptions work well for the simple situations we look at in this class. We ended with three energies we need to track at different points of a fluid: gravitational, kinetic, and interaction energy. (I'm leaving that third type of energy a mystery, but if you think enough about the water that flows slowly under your house and then streams out fast from the tap on the second floor, you can understand that the water at your tap has more gravitational energy and more kinetic energy. Where did that energy come from? What type of energy did the water lose?)