19 ms·
DC Circuit Water Analogy (1998)
- brk 5y agoThey should show an analogy between capacitors and water hammer preventers. And maybe inductors to pressure/expansion tanks.
- sidpatil 5y agoThe 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.
- azalemeth 5y agoI 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).
- madengr 5y agoInductance would be the momentum of the water; reactance to change in flow. Capacitance would be the expansion tank; reactance to change in pressure.
- deleted 5y ago[deleted]
- sandworm101 5y agoThere 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).
- mivade 5y agoNo 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.html#c1 http://hyperphysics.phy-astr.gsu.edu/hbase/electric/watcir3.....
- joezydeco 5y agoWhen I need to explain voltage+current to my inlaws, the analogy is good enough. Perfect is the enemy of done.
- shane_b 5y agoSame, 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 5y agoCould 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 5y agoThat’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.
- Freak_NL 5y agoVery likely posted on HN today because of this week's XKCD; 'Hydraulic Analogy': https://xkcd.com/2571/ https://xkcd.com/2571/
- silveira 5y agoI came here searching for this comment and it is here.
- CapitalistCartr 5y agoI'm an electrician, definitely not a plumber. But when I needed to redo my parent's irrigation system, the reverse analogy served well enough.
- eternalban 5y agowikipedia has a very comprehensive treatment of this analogy: https://en.wikipedia.org/wiki/Hydraulic_analogy https://en.wikipedia.org/wiki/Hydraulic_analogy
- yboris 5y agoA crude joke comparing electricians and plumbers: https://i.redd.it/42ah3br6r2251.jpg https://i.redd.it/42ah3br6r2251.jpg
- erwincoumans 5y agoThis video goes a bit further into the analogy, with parallel and series circuits etc: https://www.youtube.com/watch?v=7_7NO2Np5-s https://www.youtube.com/watch?v=7_7NO2Np5-s
- caseysoftware 5y agoAt 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.
- zodzedzi 5y ago> 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?
- femto 5y agoIt doesn't approach it from a thermodynamic perspective, but the following paper summarises the duality between electrics, hydraulics, acoustics and mechanics: SchÖnfeld, J. C. (1954). Analogy of hydraulic, mechanical, acoustic and electric systems. Applied Scientific Research, Section B, 3(1), 417–450. doi:10.1007/bf02919918
- toolslive 5y agoYes. 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!)
- ohmthrow 5y agoObligatory 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 5y agoThe key is to realize electricity in a circuit is kind of like data traveling through a network ;)
- Moru 5y agoExcept 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 :-)
- shadowgovt 5y agoFor fixing things, a couple of good books on home repair will do you a lot better than deep theory (both because safely manipulating high voltages in a home setting doesn't require the underlying physics so much as following the rules and because if you apply the theory too strictly, you run the risk of getting tripped up, possibly dangerously so, by somebody failing to do something to code). On the other hand, the underlying theory is very useful for if you do encounter something off code, because something off code will be doing something, and you as the homeowner are stuck figuring out what.
- mnw21cam 5y agoIt'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 https://en.wikipedia.org/wiki/Hydraulic_ram
- bullfightonmars 5y agoCheck 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-build-mechanical-circuits?ref=user_menu https://www.kickstarter.com/projects/upperstory/spintronics-...
- aidos 5y agoHas anyone tried Turing Tumble? Would you recommend it? Thinking about getting it for an upcoming bday for one of my kids.
- 317070 5y agoIt is nice, and the things you can do are amazing. As an adult I enjoyed playing it. My 9 year old brother found it quickly too hard though.
- po 5y agoI bought it and explained to my kids (7 and 3) that it's "daddy's game" and they can watch me play it but can't play it without me. My 7 year old daughter helped me up through about the first 1/3rd of the game but then quickly it became too hard. It does a good job of introducing concepts slowly but they are in fact hard concepts if you're new to them. It is actually a bit of a challenge for adults too. Mechanically, the game is good but a bit finicky to set each piece in place. That means the time between "I think I know what to do" and testing it out is a bit too long. Overall, I find it pretty fun though. (I also backed the spintronics kickstarter)
- numpad0 5y agoJust 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 5y agoIt 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.
- MatthiasWandel 5y agoUnfortunately, 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 5y agoIf 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 5y agoWhereas 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 5y agoWhile 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.
- marcodiego 5y agoI still miss the water equivalents for capacitors and inductors.
- munificent 5y agoYou 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.
- adhoc_slime 5y agoI'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 5y ago[deleted]
- shadowgovt 5y agoI don't know how hard it is to find these days, but I stumbled across a book called "There are no elections" ages ago that I found very helpful. As a student of American high schools familiar with both the water analogy and the basic electron flow theory we get in school, that book does a good job of upending both by presenting a sort of third model that, while tongue-in-cheek, fits the observations the first two models explain. Then it's sort of goes on to show how those models are all lacking because there are other things we know about electricity that don't fit any of them.
- edtechdev 5y agoThis Falstad animated circuit simulation has been the best at conceptually understanding what's going on in circuits: https://falstad.com/circuit 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.
- stathibus 5y agoFalstad is a really excellent education tool. I used it myself as an undergrad and as a tutor. Can't recommend it enough.
- gowld 5y agoA "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 5y agoThose 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 https://falstad.com/mathphysics.html I like the 2D vector field one https://falstad.com/vector https://falstad.com/vector (2d) and the 3d one https://falstad.com/vector3d https://falstad.com/vector3d. Antenna simulator: https://falstad.com/antenna https://falstad.com/antenna Waveguide is awesome too https://falstad.com/embox/guide.html 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!
- alliao 5y agotangentially 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/making-money-flow-the-moniac https://www.rbnz.govt.nz/research-and-publications/videos/ma...
- lagrange77 5y agoThere 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.
- djrconcepts 5y agoThese water circuit analogs to electric circuits remind me of Eric Laithwaite's water analogs. Several videos showing the analogs in action on youtube in The Circle of Magnetism. For example: https://www.youtube.com/watch?v=0tJfqMYHaQw https://www.youtube.com/watch?v=0tJfqMYHaQw
- shadowgovt 5y agoI've had my head buried in law too long because when I saw this headline I didn't think about electricity; I figured somebody had come up with a boneheaded way to explain a legal theory. Anyway. The water analogy is pretty good, but it'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've learned about DC and apply it to alternating current. It's a great place to start though. After getting one's head wrapped around those, I found that Kirchoff'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).