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Comment by iterance | Hacker News Reader

This seems unnecessarily negative. Teaching analogies don't need to perfectly resemble the system being taught. From a pedagogical perspective, the aim is typically to relate something unfamiliar to something familiar, like water flowing in a pipe, in order to help someone gain footing in a topic.

Further connections can be developed mathematically; electric force propagation does obey wave equations, after all. But by then the analogy has served its purpose and should be droppped in favor of more rigorous knowledge development.

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When I was in EE at Purdue, most of my profs also railed against the hydraulic model. It really messes you up when it comes time to get into higher frequency digital circuits (CPU designs were just starting to brush up against quantum problems at the time).

Why would anyone be attempting to use this analogy to learn about intermediate to advanced topics like that? That's not what learning aid analogies are for... They are for beginners to gain some initial intuition in order to get over the immediate hump of unfamiliarity with a new subject.

They wouldn't, but people would create these increasingly tortured analogies out of the same motivations that other creative people would create, say, a raytracer in Brainfuck or a pregnancy test that can run DOOM.

By the time you get into higher frequency circuits I would think you would already understand exactly where the hydraulic analogy breaks down. Most grade school students aren’t doing any kind of extremely high frequency work, let alone even basic 60hz work.

When I was taking undergrad EE classes, I don’t recall it ever coming up. I think people’s comfort with and intuition for electricity are at least as good as for water, which actually behaves in deeply unintuitive ways. We’ve been living with switches and toaster ovens for generations now, people understand resistance, voltage, and current just fine on their own terms. Or at least, water analogies don’t help because people don’t understand water any better.

Once you start dealing with EM fields and even fairly common filter designs in the AC domain, the hydraulic analogy starts breaking down and becomes an impedement to learning... so my prof would say.

I was never taught the water analogy but I saw quite a few students struggle trying to wrap their heads around a physics (EM, RF, potentials, etc) based circuit design and theory.

As a fellow EE, I was amused that the plumbing model never came up in my engineering classes, but was introduced (and re-introduced) at several levels in my physics classes.

Agree. The hydraulic analogy is a good introduction to the duality that is current and voltage — as well as, to varying degree, capacitance and resistance. But then let's just stop there.

No problem.

I completely agree. Every model is "wrong" to some degree, it's just a matter of applying the "least wrong" one in the proper context to yield the most practicable solution.

Even basic circuit theory (Kirchhoff's laws) falls apart when the preponderance of propagating wavelengths become close to the characteristic length of the propagating medium.

Then that "wrong" simplifying model must transition to the much more complex transmission line theory.

By the same analogy, one doesn't use basic Bernoulli pressure/velocity/flow equations for plumbing when dealing with chaordic or turbulent flows outside of very limited Reynolds number regimes--one has to do numeric simulations of the more general Naiver-Stokes vector differential equations.

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