When the scientists wanted to found fluid dynamics some heuristic problems were encountered. There were not physically isolated material particles as it was usual in order to apply Newtonian dynamics, and the fluid’s own lack of form and its capacity of spatial extensibility needed an imagery that orthodox Newtonian problems did not offer. As a result, in the starting point of the theoretical genesis analogy was more than just associative relation with expedient function, analogy should be able to activate and contain inside new image schemas and to regenerate the imagery needed for the solution of fluid dynamics problems. Bernoulli father and son were committed to this, especially the son.

The explanation and the determination of velocity-pressure relationship was the best contribution made by Daniel Bernoulli to the history of fluid mechanics. In the introduction of the chapter XII of his work Hydrodynamica says that the pressure of static water and the pressure of the flux of water must be clearly distinguished. Here he realized, “surprisingly”, that the pressure cannot be defined without taking into account the velocity of the flow.

Daniel presents a thought experiment based on a standard problem in order to investigate the pressure-velocity relation. The thought experiment is used within analogical reasoning with a creative function: to generate predictions for the flow phenomenon in a pipe (target) and to generate ideas for constructing model. Besides this, related with images, there is an imagery enhancement by generating extreme cases that helps tap implicit knowledge by increasing the contrast between simulations. The use of extreme cases, which seeks this contrast, is one of the clear heuristics instruments in the design of simulation; but there is another: the use of the cap with the hole as a heuristic marker to make it easier to track changes in key variables as pressure and velocity. All this simulative process establishes a source of conviction for the thinker because it is a way of generating an initial plausibility test for the model. There is a evaluation via simulation, as in the case of Maxwell's electromagnetic wheels and gears described by Nersessian (2002). Later, the conviction obtained for this qualitative model was able to develop a quantitative mathematical model to reach the famous Bernoulli's Theorem.