"Water circuit" equivalents of basic electric components

[rumborak]

There were two threads in short succession in this forum about basic electric circuitry (RC circuit, RL circuit), and it struck me that over the years I've been surprised that the "water circuit" analogy isn't used more than it is.
That is, in a system with a circular pipe that contains water:

Electrons = Water molecules
Battery = Pump
Voltage = Water pressure
Current = Water flow
Resistor = Narrow pipe

Now, what would the equivalents of the capacitor and the coil be? That's what I've been wondering.

EDIT: Ooh, a coil could be imagined as a heavy flywheel that is moved by the water current. It will oppose any change in flow through it.

 

[Quantum Defect]

There were two threads in short succession in this forum about basic electric circuitry (RC circuit, RL circuit), and it struck me that over the years I've been surprised that the "water circuit" analogy isn't used more than it is.
That is, in a system with a circular pipe that contains water:

Electrons = Water molecules
Battery = Pump
Voltage = Water pressure
Current = Water flow
Resistor = Narrow pipe

Now, what would the equivalents of the capacitor and the coil be? That's what I've been wondering.

EDIT: Ooh, a coil could be imagined as a heavy flywheel that is moved by the water current. It will oppose any change in flow through it.

A Battery is more like a water tower, I think. It just sits there with potential energy until you tap it. Water also leaks out of these over time, running down -- just like a battery.

 

[Hesch]

Now, what would the equivalents of the capacitor and the coil be? That's what I've been wondering.

A capacitor is a watertank with the inlet and outlet placed in same height (at the bottom). If more water flows in than out, the tank will be filled with water, increasing the water pressure at the bottom. (The capacitor will be charged, increasing the voltage over the capacitor).

A coil is a turbine loaded by some inertia. Water pressure will accelerate the turbine, so that water flow through the turbine gradually increases. Lowering the water pressure (or changing direction of the pressure), the inertia will drive the tubine, so that the turbine will act as a pump while decellerating.. (You cannot immediately alter the current through a coil).

 

[rumborak]

A capacitor is a watertank with the inlet and outlet placed in same height (at the bottom). If more water flows in than out, the tank will be filled with water, increasing the water pressure at the bottom. (The capacitor will be charged, increasing the voltage over the capacitor).

Hmm, but no matter how high you charge the watertank, you are not impeding the flow, right? That's what a capacitor does, on direct voltage it eventually blocks the current completely.

 

[rumborak]

Ah, a capacitor could be a simple tube with a divider plate in it, where the divider plate would be moved by the water pressure on both sides. However, a spring would be holding it in place, where there more it gets displaced from its rest position, the harder it becomes to move it further.

 

[jbriggs444]

Hmm, but no matter how high you charge the watertank, you are not impeding the flow, right? That's what a capacitor does, on direct voltage it eventually blocks the current completely.

Agreed. My picture of a "hydraulic capacitor" is a horizontal tank with a narrow inlet on one end, a narrow outlet on the other end and a rubber diaphragm in the middle.

Edit: Rumborak beat me to it.

 

[rumborak]

Lol, that's exactly what I was suggesting in my previous post. I like the rubber diaphragm idea, makes it conceptually simpler.

 

[Hesch]

Hmm,

I see, but give me another try:

It's a piston with an attached spring in a cylinder with inlet/outlet at the top/bottom of the cylinder. Water flow through the cylinder will compress/stretch the spring, resulting in a water pressure.

 

[rumborak]

That still doesn't cut off the flow on steady pressure.

jbrigg's and my equivalent does exactly that. Horizontal tube, with a rubber diaphragm in the middle. The equivalent is even good enough that you could show an isolated, charged capacitor that way. Charge the device in a water circuit so that the diaphragm is "loaded", then cap off the two sides, and remove the device. Now you got a "charged" capacitor that, when reconnected to another circuit, will unload its energy.

EDIT: Sorry, misread your post, you had changed one of the outlets to the top. Yeah, then it becomes equivalent to the rubber diaphragm device.

 

[sophiecentaur]

There are a number of Mathematical Equations that describe aspects of water flow are of the same form as some of the Equations used for electrical circuit analysis. That much is true. However, the 'Water Analogy' is actually pretty hopeless as a model for Electricity. The main problem is that there is no appreciable kinetic energy involved in the energy transfer in electric circuits. There is also the problem of open circuits and water leaking out of the open ends of pipes.

If you really really want to use an analogy, rather than dealing directly with a phenomenon then you are always welcome to try but the caveats are enormous and you will never be sure that any conclusions that are drawn from the analogue model are valid for the real thing.

Just what is the point, when the sums involved in basic Electrical theory are extremely simple and you can rely on the results?

 

[rumborak]

I don't know, what is ever the point of using analogies? I think the water analogy holds actually pretty well, and particularly, it makes for example people realize that just like water, the electron gas "bounces" off a resistor, with waves sloshing to and fro until the circuit is settled. I remember only learning about these dynamic effects pretty far into my EE, and I was annoyed because I always *thought* that's how it must happens, but the educational material up to that point had made it look as if electricity just magically knows that five elements down the circuit there's a resistor and thus it can only have this much current.

 

[OmCheeto]

There are a number of Mathematical Equations that describe aspects of water flow are of the same form as some of the Equations used for electrical circuit analysis. That much is true. However, the 'Water Analogy' is actually pretty hopeless as a model for Electricity. The main problem is that there is no appreciable kinetic energy involved in the energy transfer in electric circuits. There is also the problem of open circuits and water leaking out of the open ends of pipes.

If you really really want to use an analogy, rather than dealing directly with a phenomenon then you are always welcome to try but the caveats are enormous and you will never be sure that any conclusions that are drawn from the analogue model are valid for the real thing.

Just what is the point, when the sums involved in basic Electrical theory are extremely simple and you can rely on the results?

I thought I did a great job of explaining the simplicity of this a few years back:

I enjoy the hydraulic analogy, as it ... involved infinite numbers of water powered massless torque wrenches attached to the perimeter of two infinite sets of bicycle ratchet type gears. Except the torque wrenches don't really turn, and they expand at the speed of light, with a force circular to and in a particular direction, depending on which way the fluid is flowing. I think I stopped when I decided the time varying infinite numbers of water powered massless torque wrenches attached to the perimeter of two infinite sets of bicycle ratchet type gears required another slightly different set of infinite numbers of water powered massless torque wrenches attached to the perimeter of two infinite sets of bicycle ratchet type gears.

And my post from last week was almost flawless:

Each counters "conductance" is equal to fans/second(I) divided their level of fear of death(V).

Though, I don't think I finished my thoughts on the subject. hmmm...

So resistance would be (fear of death)/(fans/second)
which would be (fear of death seconds)/fan
fear of death seconds being equivalent to a weber(volt second)

Which is not quite right, as it is a change of a volt in a second that generates a "Weber".

I'm glad I could clear this up.

Rumborak, you are welcome.

 

[OmCheeto]

ps. Whenever I do these things, I have a weird feeling, that I'm simultaneously channeling the spirits of Dr. Seuss & Rube Goldberg, as the imagery, and complexity, get very strange.

 

[Quantum Defect]

I thought I did a great job of explaining the simplicity of this a few years back:

[snip]


fear of death seconds being equivalent to a weber(volt second)

[snip]

But a "Weber" is a barbecue grill? I guess if you used too much lighter fluid, you could have some reasonable fear of death ...
... and is it a "fear of (death seconds)" or a "(fear of death) seconds" ... ?

My favorite "analogy" of all time was in a quantum mechanics class taught by an eccentric professor. He said that time reversal invariance was like running the film backwards through a movie projector and having nobody laugh.

 

[rootone]

Water equivalent of an LED would be a hard one.

 

[OmCheeto]

Water equivalent of an LED would be a hard one.

Don't even get me started, on diodes...

I... thought I knew how diodes worked. One day, I entered university, and it seemed there was more to their life then just a simple bias. They were filled with dopes and holes and what-not. Later, I joined a science forum and probed a bit deeper, into the quantum world of diodes. And being that I had no comprehension of the quantum world, I decided I did not know how diodes worked.