Is it true that “engineers design systems to manage pressure and flow?”

This is an answer to a question originally asked on Quora.com. You can find the original here:
Is it true that “engineers design systems to manage pressure and flow?”

An electrical engineer was explaining how electricity works in buildings to me, and I got the impression that all of engineering can be boiled down to managing pressure and flow in systems. This seems too simple to me, and I think there is more to it.  Can someone help me understand what I am missing?.

Answer by Rustin Bergren:

What you’ve stumbled upon is called the Hydraulic analogy. It’s an incredibly useful tool for teaching the very basic concepts of electricity in circuits. Interestingly, the ideas of a ‘pressure’ and a ‘flow’ can be extended to mechanics and thermal systems (and computer networks and vehicle traffic engineering and on and on).

Here’s a chart from (the wikipedia page: System equivalence) showing the relationship between parameters of different systems.

(note: I have a couple of disagreements with this chart; however, pointing them out is not really not germane to the answer)
It doesn’t work perfectly, however. Notice, there isn’t an equivalent term for inductance in thermal systems. From this, I think we can gather that Thermal systems do not oscillate (I’m pretty sure).
Also, the simple fluid analogy for electrical engineering becomes pretty much useless after a first semester circuits course. It’s great for understanding the overall qualitative constructs of the stuff at hand, but it doesn’t get you much farther than that. For that matter, this simplistic fluid analogy wouldn’t get you all that far into an understanding of fluid mechanics.

So what you really have here is a case of having a hammer causing you to see everything you come in contact with to look like a nail. Indeed, we can draw analogies between numerous types of systems, though many times we have to modify the hammer a bit to make it work for that particular type of nail.

So yes, you’re right. It’s way too simple if you’re trying to reduce all of engineering to a simple metaphor. So it’s not at all about ‘pressure’ and ‘flow’ if you want to boil engineering down to something. What it can all be boiled down to is the application of mathematics and physics. In the case of RF Engineering (electrical) and Aeronautics (mechanical), it has to do with applying a lot of Vector Calculus. In the case of Control Systems Engineering (electrical/mechanical) and Heat Transfer Engineering (mechanical) it’s more about solving Partial Differential Equations (PDEs).

But, if you’re trying to explain the basics of how power distribution in a building works to a non-engineer, making a water analog (something most people can easily picture in their heads) works extremely well.