[HN Gopher] Water circuit analogy to electric circuit ___________________________________________________________________ Water circuit analogy to electric circuit Author : dynm Score : 94 points Date : 2022-01-24 16:16 UTC (6 hours ago) (HTM) web link (hyperphysics.phy-astr.gsu.edu) (TXT) w3m dump (hyperphysics.phy-astr.gsu.edu) | sandworm101 wrote: | 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). | jbay808 wrote: | > Water only ever remains inside the pipes that carry it. | | If only! My apartment was recently destroyed by water that | refused to do exactly that... | | Electricity also doesn't freeze solid, expand, and break open | its insulation; it doesn't evaporate and condense on cold | surfaces and cling there under surface tension, it doesn't drip | down. | | But the analogy is still a pretty useful one for people who | have lots of hands-on experience with water and not much with | electricity, or vise-versa. | sandworm101 wrote: | >> cling there under surface tension = Static charges. When a | walk in wool socks on a wet carpet my socks pick up water. | When I walk on a dry carpet my socks pick up electrons. | | >> expand, and break open its insulation = an arc causes by | too much electricity in too thin a pipe. | | >> it doesn't evaporate and condense on cold surfaces = | electro vapor deposition aka physical vapor deposition | teawrecks wrote: | The 2nd one would be less like an arc and more like the | wire/conductor getting too hot and melting/failing. | | Arcing (or shorting in general) would probably be more akin | to water's tendency to find the lowest point. | edmcnulty101 wrote: | Also not advised to drink electricity. | ithkuil wrote: | > For anyone desperate enough to want to find an analogy to a | light-emitting diode (LED), consider the fountain-emitting one- | way value shown in Figure 2. | mivade wrote: | No analogy is perfect. They are intended to help illustrate a | concept to gain insight. Ideally when using an analogy its | limits should also be described. Luckily the very first link | after the analogy is explained does just that: | http://hyperphysics.phy- | astr.gsu.edu/hbase/electric/watcir3..... | tzs wrote: | > Anything involving the electrical energy not inside wires has | no water analogue (ie the electromagnetic waves inside a | transformer) | | You don't even need fancy things like transformers for energy | not in the wires to be important. Even a simple DC circuit | consisting of a battery in series with a light bulb mostly | involves an electromagnetic field to transfer energy from the | battery to the light bulb, which mostly takes place outside the | wires. | | The function of the wires when it comes to energy transfer is | to carry moving charge which creates the magnetic part of the | electromagnetic field that actually carries the transferred | energy. | | Here's a pretty good explanation [1]. That video was from | January 2019, and not controversial. Veritasium did a video on | the topic in late 2021 that didn't really present things as | well and ended up being quite controversial [2]. Other well- | known YouTube channels such as EEVblog [3] and ElectroBOOM [4] | responded. | | There was also someone who bought a bunch of wire and did the | experiment as described in the Veritasium video (although | scaled down). That was discussed on HN and that discussion | contains some very interesting links [5]. | | In particular the link to a talk by Rick Hartley in this | subthread is very informative [6]. He talks about how most EMI | problems in PCB designs are due to people not taking into | account the the energy is not in the wires. | | [1] https://www.youtube.com/watch?v=C7tQJ42nGno | | [2] https://www.youtube.com/watch?v=bHIhgxav9LY | | [3] https://www.youtube.com/watch?v=VQsoG45Y_00 | | [4] https://www.youtube.com/watch?v=iph500cPK28 | | [5] https://news.ycombinator.com/item?id=29598860 | | [6] https://news.ycombinator.com/item?id=29601273 | gene-h wrote: | Hydraulic intensifiers can act as an analog of an electrical | transformer. An intensifier is a hydraulic device where a large | area piston is coupled to a small area piston. They are often | used in water jet cutters to produce high pressures. A jet | pump[0] is another device which acts sort of like a transformer | and exchanges high pressure for high flow. 'Inertance' of the | water in the pipe can act in a manner similar to inductors. | | [0]https://en.wikipedia.org/wiki/Injector#/media/File:Ejector_o | ... | joezydeco wrote: | When I need to explain voltage+current to my inlaws, the | analogy is good enough. Perfect is the enemy of done. | young_unixer wrote: | Wouldn't it be easier to just say "current is how many | electrons flow through a specific section of the wire in a | second" and "voltage is the force that makes the electrons | move"? | | It's just as easy to understand without need for analogies. | ionicgiraffe wrote: | Those two sentences that you wrote are precisely the | hydraulic analogy. If it weren't, instead of electrons it | would be charge (that can be positive or negative), or | field strength (if you explain the transitory period of a | capacitor or non-DC), and voltage would become not the | force, but a number that applies to conservative fields | that allows to calculate the capacity to do work relative | to another such number... | shane_b wrote: | Same, by the time you need to explain how transformers use | electromagnetism, they probably understand the basics of V=IR | which is really as far as the analogy goes. | tagoregrtst wrote: | Could a turbo-pump can be thought of as a very bad | transformer? able to transform a flow mv1 at a pressure P1 | to mv2 P2 where their product, power is constant (except | its way more lossy). | | Still, I think the water analogy is over used | stephen_g wrote: | That's probably a good description of the main usefulness of | the analogy - explaining to people who won't actually need to | apply the concepts. My conclusion (after years of doing | electronics design professionally, including RF) is that to | do much useful in electronics, you need to get into the habit | of thinking natively in terms of voltage and current and | resistance etc. so soon that the hydraulic analogy is | basically not worth learning at all, since the missing things | just get confusing and it becomes a distraction or blocker to | advancement until you "unlearn" many of the concepts. | | I mean, it's probably worth mentioning current and voltage | are "kind of" like flow, pressure etc., in a first lecture to | start to get the basic idea, but then warning not to think of | it as being the exactly same because that will just be | confusing later. | causality0 wrote: | There's a large difference between "applying the concepts" | and "doing useful things in electronics". The vast majority | of people barely find utility in repairing what they | already own, to say nothing of tinkering or creating | something new. | | The water analogy, is, in my opinion, the sweet spot for | people who will never own a multimeter or fire up a SPICE | program. It's the level that ought to be the expectation | for citizens of a technic civilization. | throwaway0a5e wrote: | You can do 99.999% of practical applications of electricity | with the liquid analogy, up to and including most | industrial electrical stuff (remember, check valves, | accumulators and whatnot are a thing). | | What you can't do is design a bottom dollar power supply | that uses some trick circuitry to not emit enough RF noise | to matter. | sandworm101 wrote: | >> 99.999% of practical applications of electricity | | All radio/wifi and everything involving fiber optics or | magnets. That's probably slightly more than 00.001% of | applications. | bigbillheck wrote: | > Water only ever remains inside the pipes that carry it | | If that were the case I wouldn't be paying twelve hundred bucks | and counting to fix the plumbing in my mom's house. | eternalban wrote: | wikipedia has a very comprehensive treatment of this analogy: | | https://en.wikipedia.org/wiki/Hydraulic_analogy | alliao wrote: | tangentially this reminds me of water computer on display in | reserve bank of new zealand | | behold! the MONIAC | | https://www.rbnz.govt.nz/research-and-publications/videos/ma... | CapitalistCartr wrote: | I'm an electrician, definitely _not_ a plumber. But when I needed | to redo my parent 's irrigation system, the reverse analogy | served well enough. | caseysoftware wrote: | 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 & 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. | | It led to many EEs getting a certificate in fluid & thermo | because the extra couple classes counted as tech electives and | the math was the same. | toolslive wrote: | Yes. At my university this course was called "Systems theory". | Electrical networks, mechanical systems, hydraulic networks | were shown to have laws that have the same shape. They also | only gave the course after letting you struggle with | electricity, mechanics, fuild mechanics, ... for a few years. I | guess to make you appreciate it more (which I did!) | zodzedzi wrote: | > One of the big class combos was Electrical Systems, | Mechanical Systems, and Fluid & Thermodynamic systems where you | work through from the laws of thermodynamics to how they apply | in each of the areas. | | I would love to find a book with this type of presentation. Do | you happen to remember which textbooks were used for this | class? | erwincoumans wrote: | This video goes a bit further into the analogy, with parallel and | series circuits etc: https://www.youtube.com/watch?v=7_7NO2Np5-s | marcodiego wrote: | I still miss the water equivalents for capacitors and inductors. | munificent wrote: | You can think of a capacitor as sort of like a rubber membrane | stretched across the pipe. It allows some water to flow as it | distends but then stops. When distended like that, it has some | reverse pressure that wants to flow back. | | An inductor would be something like a propeller/impeller | attached to a flywheel. | ohmthrow wrote: | Obligatory newb question: | | I recently got into electronics/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/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). | | A close family member was an EE/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. | | 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. | jrumbut wrote: | The key is to realize electricity in a circuit is kind of like | data traveling through a network ;) | Moru wrote: | Except the wifi has it's own wifi that has it's own | interference that is having it's own echo. Go too low down | the frequency hole and you get so lost :-) | Freak_NL wrote: | Very likely posted on HN today because of this week's XKCD; | 'Hydraulic Analogy': https://xkcd.com/2571/ | silveira wrote: | I came here searching for this comment and it is here. | edtechdev wrote: | This Falstad animated circuit simulation has been the best at | conceptually understanding what's going on in circuits: | https://falstad.com/circuit | | Click on the 'Circuits' menu to see dozens of example circuits. | | One issue with the hydraulic/fluid analogy is the "empty pipe" | misconception - we forget or don't know that in electrical | circuits, the circuit is a closed loop. An example of this | misconception is that beginners sometimes think the current | "wears out" 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't | perfect. As a next level, I like showing animations/simulations | that show the role of charge on the 'outside' of the wire in | steering current flow, as well as magnetic fields surrounding the | wire. | gowld wrote: | A "closed" circuit is just an open circuit plus a pump | (electron pump or water pump). | | Open circuits work fine if there is a powerful source of | electricity (like a a radio) and a sink (like the Earth), and | same for water (an icy comet crashing into a cliff, making a | waterfall). | | An open water circuit is full of stationary water. | rdtsc wrote: | Those are exceptional. I remember gaining really nice math and | physics intuition from his "applets" years ago. Yes, those | started as Java applets if anyone still remembers those. | | Here are math and physics ones: | https://falstad.com/mathphysics.html | | I like the 2D vector field one https://falstad.com/vector (2d) | and the 3d one https://falstad.com/vector3d. | | Antenna simulator: https://falstad.com/antenna | | Waveguide is awesome too https://falstad.com/embox/guide.html. | Don't forget to pick various modes in the little square at the | bottom. | | If Paul Falstad comes around these parts, thank you for | creating and sharing those! | stathibus wrote: | Falstad is a really excellent education tool. I used it myself | as an undergrad and as a tutor. Can't recommend it enough. | mnw21cam wrote: | It's missing capacitors and inductors. | | 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'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). https://en.wikipedia.org/wiki/Hydraulic_ram | lagrange77 wrote: | Yes, that's always been my favourite hydraulic-electrical | analogy! | hwillis wrote: | Acoustics is a more direct parallel, and even uses the same | unit- the acoustic Ohm. The hydraulic Ohm also exists, but is | not really used. | | Helmholtz resonators[1] are used to provide capacitive acoustic | impedance in a gas system. Archetypically a beautiful hollow | copper sphere. Ported subwoofers use the same formulas, as do | some types of automotive exhaust. Exhausts use a long pipe and | cylindrical section to form a low-pass filter, which transforms | the individual exhaust bursts of an engine into a smooth | continuous flow. Two stroke exhausts[2] are band-pass filters | that improve compression by putting backpressure on the engine | at the correct time. | | [1]: https://en.wikipedia.org/wiki/Helmholtz_resonance | | [2]: | https://en.wikipedia.org/wiki/Expansion_chamber#/media/File:... | amelius wrote: | > The system uses an inductor (a long straight pipe, where the | water has momentum), | | How would you model mutual inductance in other circuits? | jcims wrote: | A hydraulic cylinder connecting the systems would work. It | maps voltage (pressure) between two disconnected systems | through a ratio of windings (piston area). It only creates | flow when there is a change in voltage (pressure) and current | (flow), and if the circuit is open on the induced side then | the transfer of energy is limited to the capacitance | (compressibility) in the circuit. | bullfightonmars wrote: | Check out Spintronics, it's a game/kit for building mechanical | analogs for electric circuits. It's coming out sometime this | year from the same team that made Turing Tumble. | | https://www.kickstarter.com/projects/upperstory/spintronics-... | aidos wrote: | Has anyone tried Turing Tumble? Would you recommend it? | Thinking about getting it for an upcoming bday for one of my | kids. | lagrange77 wrote: | There are also some very interesting analogies with mechanical | and thermo dynamical* systems. | | 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 'govern' those differential | equations. | | *Fun fact: Classical thermals systems do not have an inductive | element. That'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. | MatthiasWandel wrote: | Unfortunately, water isn't as simple as electricity. | | 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. | mikewarot wrote: | If you force enough current through a wire, the Lorenz force | can cause it to pinch in on itself and disintegrate. Copper | wires aren't so simple at high currents, high voltages, or high | frequencies. | CamperBob2 wrote: | _Whereas for electricity, voltage drop is always proportional | to current._ | | The water metaphor works fine for many DC circuit comparisons, | up to and including basic transistor operation. Meanwhile, at | AC, your statement above doesn't hold up much better than the | water analogy would. Lots of additional terms come into play... | skin effect, radiative losses, displacement current and phasor | relationships, even quantum effects. | | Every once in a while, a huge Internet argument springs up | among people who don't understand that the Ohm and Kirchoff | laws represent the steady-state map and not the time-variant | territory. Do a search on eevblog for "Lewin," for instance. | (Actually that's terrible advice. Don't do that, and forget I | said anything.) | lagrange77 wrote: | While this is true, these analogies do have limits of | applicability, like all models have. They are only valid down | to a specific point of abstraction and only within certain | bounds. You just have to be aware of the limits of your | analogies, to use them as a tool, an educational one in this | context. | | That's how modelling works. | brk wrote: | They should show an analogy between capacitors and water hammer | preventers. And maybe inductors to pressure/expansion tanks. | sidpatil wrote: | The analogies I've heard are that a capacitor is like a rubber | membrane in line with the water pipe, and that an inductor is | like a flywheel being driven by a turbine. | [deleted] | madengr wrote: | Inductance would be the momentum of the water; reactance to | change in flow. Capacitance would be the expansion tank; | reactance to change in pressure. | azalemeth wrote: | I think the inductor one only makes sense if you imagine the | flywheel being driven with huge buckets -- such that the | voltage drop is massive if [?]V/[?]t is large (with analogy | to L [?]I/[?]t). I'm far from convinced that is totally right | though, as you can easily have arbitrarily high voltages with | switched circuits and inductors, but not necessarily with | turbines... | | I guess a transistor is a little man twiddling a valve | according to a dial in the "water model" of electricity, any | through-space effects are due to leaks, and nonlinear | components like MOSFETs are a bit more creatively explained. | (E.g. Source: water reservoir; drain: water reservoir; gate: | gate between source and drain reservoirs, driven by an | utterly mad person who follows interesting rules. Oh, and | inexplicably he's a bit stronger than transistor man too). | yboris wrote: | A crude joke comparing electricians and plumbers: | | https://i.redd.it/42ah3br6r2251.jpg | numpad0 wrote: | 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. | | 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. | | Funny that sometimes the water analogy also works the other way | around. | hwillis wrote: | It can get you into trouble in real (high pressure, | specifically) hydraulic circuits, since hydraulic | pumps/actuators are almost always flow (current) sources | instead of voltage/pressure sources. It's almost a fundamental | rule, since liquids are so incompressible. A hydraulic | reservoir under a very high pressure will only provide a tiny | amount of flow before the pressure drops to zero. | | The opposite is also true; if the flow out of a pump is blocked | then the pressure will immediately climb extremely high and | usually break things. Once you get into the weeds with | transistors etc you obviously also have to worry a lot more | about currents, but with hydraulics it's always about the flow. | adhoc_slime wrote: | I've been recently learning all about hobby electronics recently | (circuit design, microcontrollers, basic components so far), so I | want to give a beginner's perspective, and honestly this water | pressure /flow analogy is actually really distracting and | misleading as soon as you get past the basics of circuits and | components. | | If you'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't apply. | Or at least heavily stress that these are analogies and not to | expect that this "water circuit" analogy will hold forever. | [deleted] ___________________________________________________________________ (page generated 2022-01-24 23:03 UTC)