DC Circuit Water Analogy (1998)

This Falstad animated circuit simulation has been the best at conceptually understanding what&#x27;s going on in circuits: <a href="https:&#x2F;&#x2F;falstad.com&#x2F;circuit" rel="nofollow">https:&#x2F;&#x2F;falstad.com&#x2F;circuit</a><p>Click on the &#x27;Circuits&#x27; menu to see dozens of example circuits.<p>One issue with the hydraulic&#x2F;fluid analogy is the &quot;empty pipe&quot; misconception - we forget or don&#x27;t know that in electrical circuits, the circuit is a closed loop. An example of this misconception is that beginners sometimes think the current &quot;wears out&quot; as it goes along the wire. The Falstad simulation shows a line of moving dots that move faster or slower depending on the current - a little more like a train moving in a pipe - which helps counter this misconception, although it, too, isn&#x27;t perfect. As a next level, I like showing animations&#x2F;simulations that show the role of charge on the &#x27;outside&#x27; of the wire in steering current flow, as well as magnetic fields surrounding the wire.

It&#x27;s missing capacitors and inductors.<p>Did you know - a boost switching regulator was used to pump water up to the top of a garden in Victorian times. The regulator uses the water pipe analogy to electricity, except electricity hadn&#x27;t really been invented then. The system uses an inductor (a long straight pipe, where the water has momentum), and a switch (a flap that closes and opens regularly), with a diode (one-way valve) and a capacitor (a container with a pressurised air cavity). <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Hydraulic_ram" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Hydraulic_ram</a>

At my engineering undergrad, the mechanical, computer, and electrical engineers had effectively the same curriculum through our sophomore year. One of the big class combos was Electrical Systems, Mechanical Systems, and Fluid &amp; Thermodynamic systems where you work through from the laws of thermodynamics to how they apply in each of the areas. It was mind blowing when you realize how much of the underlying reasoning - and therefore resulting formulas - are nearly identical.<p>It led to many EEs getting a certificate in fluid &amp; thermo because the extra couple classes counted as tech electives and the math was the same.

There are serious limits to the analogy. Water only ever remains inside the pipes that carry it. Anything involving the electrical energy not inside wires has no water analogue (ie the electromagnetic waves inside a transformer).

I&#x27;m an electrician, definitely <i>not</i> a plumber. But when I needed to redo my parent&#x27;s irrigation system, the reverse analogy served well enough.

Unfortunately, water isn&#x27;t as simple as electricity.<p>Pipes almost always end up having turbulent flow inside, in which case, pressure drop is proportional to flow rate squared. Whereas for electricity, voltage drop is always proportional to current. This leads to problems when trying to use circuit analogies when trying to solve for pressure drop in a system of pipes.

There are also some very interesting analogies with mechanical and thermo dynamical* systems.<p>What i find even more interesting, is that those analogies are no lucky coincidence. The rules of dynamical systems apply on a higher level. The differential equations governing those systems do not care, how the concepts of inertia, capacitance or resistance are realised in a real world system. Those are implementation details. Neither do physical principles, like the principle of least action, which &#x27;govern&#x27; those differential equations.<p>*Fun fact: Classical thermals systems do not have an inductive element. That&#x27;s why there are no oscillations in thermal systems. You need two kinds of energy storage for that, so that the energy can switch between them.

Just the other day I was thinking about experimenting with some hydraulic or pneumatic cylinders, and I saw photo of a dual input cylinder with couples of pipes going in and out interconnected with a power source and a three position valve to hold or release pressure coming from either of two ports.<p>I looked at the photo and the description and suddenly realized I was looking at a XOR’d MOSFET low side switch circuit made of pipes and valves.<p>Funny that sometimes the water analogy also works the other way around.

I&#x27;ve had my head buried in law too long because when I saw this headline I didn&#x27;t think about electricity; I figured somebody had come up with a boneheaded way to explain a legal theory.<p>Anyway.<p>The water analogy is pretty good, but it&#x27;s important to not get too wrapped up in it. In some very fundamental ways, electricity is not like water, and believing it is will trip you up when you get into more complicated circuits or try to take what you&#x27;ve learned about DC and apply it to alternating current. It&#x27;s a great place to start though.<p>After getting one&#x27;s head wrapped around those, I found that Kirchoff&#x27;s loop and junction rules were great, because they make intuitive sense (junction because matter is not created or destroyed, and loop because the value of a thing has to be equal to itself, so no matter what path you take around the circuit, when you return to a point of origin it must be true that the point of origin has the same voltage at the end of the path as it did at the beginning).

wikipedia has a very comprehensive treatment of this analogy:<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Hydraulic_analogy" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Hydraulic_analogy</a>

They should show an analogy between capacitors and water hammer preventers. And maybe inductors to pressure&#x2F;expansion tanks.

I&#x27;ve been recently learning all about hobby electronics recently (circuit design, microcontrollers, basic components so far), so I want to give a beginner&#x27;s perspective, and honestly this water pressure &#x2F;flow analogy is actually really distracting and misleading as soon as you get past the basics of circuits and components.<p>If you&#x27;re an educator please reconsider using these analogies that fall apart later on becuase in more complex concepts but the analogy may stick on in your students head when it doesn&#x27;t apply. Or at least heavily stress that these are analogies and not to expect that this &quot;water circuit&quot; analogy will hold forever.

Very likely posted on HN today because of this week&#x27;s XKCD; &#x27;Hydraulic Analogy&#x27;: <a href="https:&#x2F;&#x2F;xkcd.com&#x2F;2571&#x2F;" rel="nofollow">https:&#x2F;&#x2F;xkcd.com&#x2F;2571&#x2F;</a>

A crude joke comparing electricians and plumbers:<p><a href="https:&#x2F;&#x2F;i.redd.it&#x2F;42ah3br6r2251.jpg" rel="nofollow">https:&#x2F;&#x2F;i.redd.it&#x2F;42ah3br6r2251.jpg</a>

These water circuit analogs to electric circuits remind me of Eric Laithwaite&#x27;s water analogs. Several videos showing the analogs in action on youtube in The Circle of Magnetism. For example: <a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=0tJfqMYHaQw" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=0tJfqMYHaQw</a>

tangentially this reminds me of water computer on display in reserve bank of new zealand<p>behold! the MONIAC<p><a href="https:&#x2F;&#x2F;www.rbnz.govt.nz&#x2F;research-and-publications&#x2F;videos&#x2F;making-money-flow-the-moniac" rel="nofollow">https:&#x2F;&#x2F;www.rbnz.govt.nz&#x2F;research-and-publications&#x2F;videos&#x2F;ma...</a>

This video goes a bit further into the analogy, with parallel and series circuits etc: <a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=7_7NO2Np5-s" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=7_7NO2Np5-s</a>

Obligatory newb question:<p>I recently got into electronics&#x2F;electricity and I have been trying to put together a course for myself, mostly for the kind of work that involves fixing things (power supplies, small house appliances, and so on) but also for having a good understanding for how things work. Of course the field is huge and there’s all sorts of applications out there. I’m a long time software dev and I’ve delved into all sorts of software-oriented subjects over the years, so I’m hoping I can apply some of this knowledge, at least from a troubleshooting&#x2F;analysis perspective. But oh boy is this difficult due to electromagnetism and not being able to really visualize these things (not without an oscilloscope I suppose).<p>A close family member was an EE&#x2F;technician and they ran a repair service for appliances for many decades - anything and everything, TVs, radios, kitchen appliances, industrial machinery, and so on. Sadly they passed away and I don’t know anyone personally I can ask about where to begin and how to approach this.<p>Any recommendations for curriculum? I started with Make: Electronics 3rd Ed and a half dozen or so online resources, like the Khan Academy series and some other undergraduate level videos on circuit analysis and such. I really like the electricity misconceptions site as well.

I still miss the water equivalents for capacitors and inductors.