[HN Gopher] Water circuit analogy to electric circuit
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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]
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