water analogy- a simple calculator

[George Herold]

On Jan 10, 11:32 am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

On Mon, 10 Jan 2011 15:05:06 +0100, "F. Bertolazzi"

TOGLIe...@MAIUSCOLEtdd.it> wrote:
John Larkin:

Except that most people don't understand the fluid situation to start,

Right. That's why this analogy is precious.

Everybody that has played with a garden hose as a kid has wondered why, if
you obstruct its end with the thumb, the water jet goes farther.

The solution to this apparent absurdity not only explains them Ohms law,
but also entices their curiosity by satisfying a long-standing question.

OK, what's the electrical equivalent of the finger-on-the-hose thing?
Schematic, please.

Hmm that's not easy to do... Water spraying out the end of the hose
looks like a circuit spitting electrons.... Expect for HV stuff we
usually keep all the electrons in the conductor. So best to keep the
water in the hose.
All analogies fall apart at some point. I don't mind the water
analogy. I like to think of the potential as water at different
heights in the gravitaional potential. (Really the same as the
pressure, but...) I don't know much fluid dynamics but isn't there
some low velocity limit where a pipe looks 'ohmic'. (Double the flow
for double the pressure.)

George H.

and lots of people don't do these sorts of physical analogies very
well. I find it easier to just explain the electricity.

Probably that's the reason why most of the ITIS (vocational high school)
graduates I interviewed don't know Ohm's law. We should make the teaching
of the water analogy compulsory in schools.

There is no equivalent of Ohm's Law in fluid flow. There's not much
point in teaching electronics qualitatively.

John

 

[Darwin]

On 10 Gen, 00:36, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

As I said, it's a weak analogy. You have to misunderstand fluid flow
for it to even sort of work. I've never liked using plumbing to
explain electronics.

A few years ago, a guy from CCD design has tried for four hours to
convince me and a few colleagues of mine that some kind of water
analogy was the best thing around to teach the behavior of the MOS
transistor. The problem is that I am much more used to electronics
than water piping, so basically I needed to understand the water
equivalent by coming back to the electronic circuit
I am not able to say if a beginner can find those kind of analogies
useful (or just funny), but usually I do not see things that way.

 

[F. Bertolazzi]

George Herold:

Hmm that's not easy to do... Water spraying out the end of the hose
looks like a circuit spitting electrons....

Wait! Who sys that water is similar to electrons?

I was talking about electric current, that flows from a high reservoir
potential to *ground* potential, throung an acqueduct and hose that have a
fixed resistance and a variable thumb

Electrons, by the way, go the other direction.

 

[Darwin]

On 11 Gen, 00:28, "F. Bertolazzi" <TOGLIe...@MAIUSCOLEtdd.it> wrote:

Electrons, by the way, go the other direction.

One of the problems I had with the water analogy that was given to me
is that the guy I described in my previous message represented the
flow of electrons with the flow of water. Maybe it was a nice thing
for him, but it was utterly unpleasant for me since all signs were
reversed when taking into account the currents...

 

[George Herold]

On Jan 10, 4:59 pm, Darwin <davbu...@tiscali.it> wrote:

On 10 Gen, 00:36, John Larkin

jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
As I said, it's a weak analogy. You have to misunderstand fluid flow
for it to even sort of work. I've never liked using plumbing to
explain electronics.

A few years ago, a guy from CCD design has tried for four hours to
convince me and a few colleagues of mine that some kind of water
analogy was the best thing around to teach the behavior of the MOS
transistor. The problem is that I am much more used to electronics
than water piping, so basically I needed to understand the water
equivalent by coming back to the electronic circuit  
I am not able to say if a beginner can find those kind of analogies
useful (or just funny), but usually I do not see things that way.

So my understanding of FET's is that they are just conduction
channels, that get cut off as voltage (pressure) is applied. There
can be all sorts of pinch-off effects and complications as you try and
close the gate too fast. But the water analogy looks pretty good for
FETs.

I've never measured the pressure drop along a tube of known size, flow
velocity and...(and the fluid equivalent of resistivity)

George H.

 

[George Herold]

On Jan 10, 6:28 pm, "F. Bertolazzi" <TOGLIe...@MAIUSCOLEtdd.it> wrote:

George Herold:

Hmm that's not easy to do... Water spraying out the end of the hose
looks like a circuit spitting electrons....

Wait! Who sys that water is similar to electrons?

I was talking about electric current, that flows from a high reservoir
potential to *ground* potential, throung an acqueduct and hose that have a
fixed resistance and a variable thumb

Electrons, by the way, go the other direction.

Oh, I thought that was the analogy. The flow of electrons looks like
the flow of water. At some low enough velocity...I think it must
work?

George H.

 

[Michael A. Terrell]

John Larkin wrote:

OK, what's the electrical equivalent of the finger-on-the-hose thing?
Schematic, please.

A transformer: High flow at low pressure is transformed into low
flow at high pressure.


--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.

 

[Michael A. Terrell]

Darwin wrote:

On 10 Gen, 00:36, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

As I said, it's a weak analogy. You have to misunderstand fluid flow
for it to even sort of work. I've never liked using plumbing to
explain electronics.

A few years ago, a guy from CCD design has tried for four hours to
convince me and a few colleagues of mine that some kind of water
analogy was the best thing around to teach the behavior of the MOS
transistor. The problem is that I am much more used to electronics
than water piping, so basically I needed to understand the water
equivalent by coming back to the electronic circuit
I am not able to say if a beginner can find those kind of analogies
useful (or just funny), but usually I do not see things that way.

It's like a valve that is controlled by a low flow of water. They
are used in irrigation work.


--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.

 

[George Herold]

On Jan 10, 7:28 pm, Darwin <davbu...@tiscali.it> wrote:

On 11 Gen, 00:28, "F. Bertolazzi" <TOGLIe...@MAIUSCOLEtdd.it> wrote:

Electrons, by the way, go the other direction.

One of the problems I had with the water analogy that was given to me
is that the guy I described in my previous message represented the
flow of electrons with the flow of water. Maybe it was a nice thing
for him, but it was utterly unpleasant for me since all signs were
reversed when taking into account the currents...

Yeah, that's a problem. Once you learn about semiconductors and
holes, you can just remeber that in our system the holes flow in the
positve direction. (that was a joke) No analogy is perfect. It's
better to think about the real electrons, once the analogy is
understood.

George H.

 

[John Larkin]

On Mon, 10 Jan 2011 12:17:30 -0800 (PST), George Herold
<ggherold@gmail.com> wrote:

On Jan 10, 11:32 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Mon, 10 Jan 2011 15:05:06 +0100, "F. Bertolazzi"

TOGLIe...@MAIUSCOLEtdd.it> wrote:
John Larkin:

Except that most people don't understand the fluid situation to start,

Right. That's why this analogy is precious.

Everybody that has played with a garden hose as a kid has wondered why, if
you obstruct its end with the thumb, the water jet goes farther.

The solution to this apparent absurdity not only explains them Ohms law,
but also entices their curiosity by satisfying a long-standing question.

OK, what's the electrical equivalent of the finger-on-the-hose thing?
Schematic, please.

Hmm that's not easy to do... Water spraying out the end of the hose
looks like a circuit spitting electrons.... Expect for HV stuff we
usually keep all the electrons in the conductor. So best to keep the
water in the hose.
All analogies fall apart at some point. I don't mind the water
analogy. I like to think of the potential as water at different
heights in the gravitaional potential. (Really the same as the
pressure, but...) I don't know much fluid dynamics but isn't there
some low velocity limit where a pipe looks 'ohmic'. (Double the flow
for double the pressure.)

A true anology uses the same equations, with the same solutions. A
mass-spring-dashpot mechanical system is mathematically congruent to
an R-L-C circuit. A garden hose and a finger aren't congruent to any
circuit I know of.

The water flow analogy only works at low Reynolds' numbers. Liquids
are horribly nonlinear.

It's easier to just directly explain the physics, and the math, of
electricity. There's very little electronics you can do without the
math.

John

 

[F. Bertolazzi]

Michael A. Terrell:

John Larkin wrote:

OK, what's the electrical equivalent of the finger-on-the-hose thing?
Schematic, please.

A transformer: High flow at low pressure is transformed into low
flow at high pressure.

Humm. Maybe John is right.

 

[F. Bertolazzi]

John Larkin:

A true anology uses the same equations, with the same solutions. A
mass-spring-dashpot mechanical system is mathematically congruent to
an R-L-C circuit.

That's the best one for explaining AC circuits. But what about DC circuits?

A garden hose and a finger aren't congruent to any circuit I know of.

Gosh, I'm sorry that my explanation was not clear enough.

The water flow analogy only works at low Reynolds' numbers. Liquids
are horribly nonlinear.

Sure, the first thing one thinks about when talking about pipes and water
is turbulence, in particular when they're used as an example.

It's easier to just directly explain the physics, and the math, of
electricity.

Yes, I've seen the results in my interviews. A couple of months after
finishing school they're back to blank.

There's very little electronics you can do without the math.

This platitude should validate the previous mirror climb?

 

[Bob Masta]

On Mon, 10 Jan 2011 21:02:33 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

A true anology uses the same equations, with the same solutions. A
mass-spring-dashpot mechanical system is mathematically congruent to
an R-L-C circuit.

Agreed in principle, but there can be serious debate over
the proper analogy even in this basic RLC case. Consider
that with a series connection, current is analogous to force
in that it is identical in all elements, while the voltage
drop across each element is analogous to relative velocity.
That doesn't fit well with the voltage-as-pressure concept.


Mechanical engineers use different analogies as needed, and
can make the math work out even when there isn't much
intuitive connection (to this poor EE, at least!).

Best regards,


Bob Masta

DAQARTA v6.00
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, FREE Signal Generator
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Science with your sound card!

 

[John Fields]

On Sun, 09 Jan 2011 15:36:16 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Sun, 09 Jan 2011 05:56:29 -0600, John Fields
jfields@austininstruments.com> wrote:

On Fri, 07 Jan 2011 20:29:09 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Thu, 06 Jan 2011 13:12:39 +0100, tuinkabouter
dachthetniet@net.invalid> wrote:

Op 6-1-2011 10:49, F*cking French schreef:
Hello,

I'm a designer, and I don't know much about electronics and water
analogy...
But I was wondering if a very basic calculator could be made with
water.

Lets say a circuit able to + and - numbers and display them.

I have no idea how complex such a circuit would be.

There is no analogy between electronics and water.
The only analogy i know is teh analogy between water and electricity.

Pressure is voltage.
Flow is current.

It's a weak analogy, because the equations don't match. You can't
apply Ohms-law type reasoning to fluid flow because pressure drop is
nonlinear on fluid flow.

John

---
So what?

It's still an excellent way of introducing someone unfamiliar with the
concepts of voltage, current, and resistance to their fluid analogs of
pressure, flow, and pipe diameter.

Except that most people don't understand the fluid situation to start,

---
Really?
Got a reference?
---

and lots of people don't do these sorts of physical analogies very
well.

---
Bullshit.
---

I find it easier to just explain the electricity.

---
Because, since it's convenient for you, you don't have to bother
constructing an analogy which might get the newbie over the hump, and
you get to demean anyone who doesn't understand how things work
according to his highness' high-handed "teaching" strategies.
---

And, as far as Ohm's law goes, if pressure (voltage) increases while
resistance (pipe diameter) remains constant, then current (flow) will
increase, so the _reasoning_ is the same in either case regardless of
the equations.

As I said, it's a weak analogy.

---
As _you_ said?

That's just more of your posturing and is supposed to conjure up the
image of you being incarnate and your word being incontrovertible.

Contrary to your statement, it's a very strong analogy, qualitatively,
and readily lends itself to a newbie's being able to grasp the
concepts of voltage, resistance, and current as analogies of fluid
characteristics which are palpable.
---

You have to misunderstand fluid flow for it to even sort of work.

---
Well, then, since you stated earlier:

"Except that most people don't understand the fluid situation to
start",

it shouldn't be much of a stretch to leave what doesn't matter out of
the water analogy and use what's salient to explain the basic concepts
of electricity.
---

I've never liked using plumbing to explain electronics.

---
You don't like _anything_ you disagree with, and have demonstrated
time and time again that you'll lie and cheat in order to keep from
having to admit that what you disagreed with was right.

---
JF

 

[John Fields]

On Mon, 10 Jan 2011 08:32:11 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Mon, 10 Jan 2011 15:05:06 +0100, "F. Bertolazzi"
TOGLIeset@MAIUSCOLEtdd.it> wrote:

John Larkin:

Except that most people don't understand the fluid situation to start,

Right. That's why this analogy is precious.

Everybody that has played with a garden hose as a kid has wondered why, if
you obstruct its end with the thumb, the water jet goes farther.

The solution to this apparent absurdity not only explains them Ohms law,
but also entices their curiosity by satisfying a long-standing question.

OK, what's the electrical equivalent of the finger-on-the-hose thing?
Schematic, please.

---
View in Courier:
WIRE NEEDLE POINT
+-----------------------+ / /
+--|+ HIGH VOLTAGE SUPPLY -|=====---
| +-----------------------+
GND
---

and lots of people don't do these sorts of physical analogies very
well. I find it easier to just explain the electricity.

Probably that's the reason why most of the ITIS (vocational high school)
graduates I interviewed don't know Ohm's law. We should make the teaching
of the water analogy compulsory in schools.

There is no equivalent of Ohm's Law in fluid flow. There's not much
point in teaching electronics qualitatively.

John
---

JF

 

[John Fields]

On Mon, 10 Jan 2011 21:02:33 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Mon, 10 Jan 2011 12:17:30 -0800 (PST), George Herold
ggherold@gmail.com> wrote:

All analogies fall apart at some point. I don't mind the water
analogy. I like to think of the potential as water at different
heights in the gravitaional potential. (Really the same as the
pressure, but...) I don't know much fluid dynamics but isn't there
some low velocity limit where a pipe looks 'ohmic'. (Double the flow
for double the pressure.)

A true anology uses the same equations, with the same solutions. A
mass-spring-dashpot mechanical system is mathematically congruent to
an R-L-C circuit. A garden hose and a finger aren't congruent to any
circuit I know of.

---
But congruence isn't necessary for an analogy to be valid.

For example, a 3-4-5 right triangle is like a 9-16-25 right triangle,
and they're analogous to each other, but they'r not congruent
---

The water flow analogy only works at low Reynolds' numbers. Liquids
are horribly nonlinear.

---
So what?

Just don't bring up Reynolds numbers when using the water analogy and,
since hardly anyone understands fluid dynamics - according to you -
the water won't be muddied.
---

It's easier to just directly explain the physics, and the math, of
electricity.

---
For the instructor, no doubt.

But not so easy necesarily, for the student to understand the
explanation, and that's where analogy is useful.
---

There's very little electronics you can do without the math.

---
From: http://en.wikipedia.org/wiki/Platitude

"A platitude is a trite, meaningless, biased, or prosaic statement,
often presented as if it were significant and original."

---
JF

 

[George Herold]

On Jan 11, 12:02 am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

On Mon, 10 Jan 2011 12:17:30 -0800 (PST), George Herold





ggher...@gmail.com> wrote:
On Jan 10, 11:32 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Mon, 10 Jan 2011 15:05:06 +0100, "F. Bertolazzi"

TOGLIe...@MAIUSCOLEtdd.it> wrote:
John Larkin:

Except that most people don't understand the fluid situation to start,

Right. That's why this analogy is precious.

Everybody that has played with a garden hose as a kid has wondered why, if
you obstruct its end with the thumb, the water jet goes farther.

The solution to this apparent absurdity not only explains them Ohms law,
but also entices their curiosity by satisfying a long-standing question.

OK, what's the electrical equivalent of the finger-on-the-hose thing?
Schematic, please.

Hmm that's not easy to do... Water spraying out the end of the hose
looks like a circuit spitting electrons.... Expect for HV stuff we
usually keep all the electrons in the conductor.  So best to keep the
water in the hose.
All analogies fall apart at some point.  I don't mind the water
analogy.  I like to think of the potential as water at different
heights in the gravitaional potential.  (Really the same as the
pressure, but...)  I don't know much fluid dynamics but isn't there
some low velocity limit where a pipe looks 'ohmic'.  (Double the flow
for double the pressure.)

A true anology uses the same equations, with the same solutions. A
mass-spring-dashpot mechanical system is mathematically congruent to
an R-L-C circuit. A garden hose and a finger aren't congruent to any
circuit I know of.

That's a nice analogy too. It's nice to be able to go back and forth
'cause sometimes your brain is better as seeing things with a
different perspective. And by looking at where the analogies fail,
you can learn more about both systems.

Oh if the mechanical system has a damping term that doesn't go as the
velocity then you can get different behaviour. (Just like the water
analogy.)


Scroll down here till you get to damping, down near the bottom.

http://www.teachspin.com/instruments/tho/experiments.shtml

You can see friction damping, damping ~ velocity in the middle pic and
v^2 damping... only the middle one matches an RCL circuit.

The frictional damping is kinda interesting. The thing just stops at
some point and that point is *not* (in general) the equilibrium
position.

George H.

The water flow analogy only works at low Reynolds' numbers. Liquids
are horribly nonlinear.

It's easier to just directly explain the physics, and the math, of
electricity. There's very little electronics you can do without the
math.

John- Hide quoted text -

- Show quoted text -

 

[John Larkin]

On Tue, 11 Jan 2011 13:51:52 GMT, N0Spam@daqarta.com (Bob Masta)
wrote:

On Mon, 10 Jan 2011 21:02:33 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

A true anology uses the same equations, with the same solutions. A
mass-spring-dashpot mechanical system is mathematically congruent to
an R-L-C circuit.

Agreed in principle, but there can be serious debate over
the proper analogy even in this basic RLC case. Consider
that with a series connection, current is analogous to force
in that it is identical in all elements, while the voltage
drop across each element is analogous to relative velocity.
That doesn't fit well with the voltage-as-pressure concept.


Mechanical engineers use different analogies as needed, and
can make the math work out even when there isn't much
intuitive connection (to this poor EE, at least!).

Why do MEs need analogies? They can see and feel their stuff!

John

 

[John Larkin]

On Tue, 11 Jan 2011 08:24:10 -0800 (PST), George Herold
<ggherold@gmail.com> wrote:

On Jan 11, 12:02 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Mon, 10 Jan 2011 12:17:30 -0800 (PST), George Herold





ggher...@gmail.com> wrote:
On Jan 10, 11:32 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Mon, 10 Jan 2011 15:05:06 +0100, "F. Bertolazzi"

TOGLIe...@MAIUSCOLEtdd.it> wrote:
John Larkin:

Except that most people don't understand the fluid situation to start,

Right. That's why this analogy is precious.

Everybody that has played with a garden hose as a kid has wondered why, if
you obstruct its end with the thumb, the water jet goes farther.

The solution to this apparent absurdity not only explains them Ohms law,
but also entices their curiosity by satisfying a long-standing question.

OK, what's the electrical equivalent of the finger-on-the-hose thing?
Schematic, please.

Hmm that's not easy to do... Water spraying out the end of the hose
looks like a circuit spitting electrons.... Expect for HV stuff we
usually keep all the electrons in the conductor.  So best to keep the
water in the hose.
All analogies fall apart at some point.  I don't mind the water
analogy.  I like to think of the potential as water at different
heights in the gravitaional potential.  (Really the same as the
pressure, but...)  I don't know much fluid dynamics but isn't there
some low velocity limit where a pipe looks 'ohmic'.  (Double the flow
for double the pressure.)

A true anology uses the same equations, with the same solutions. A
mass-spring-dashpot mechanical system is mathematically congruent to
an R-L-C circuit. A garden hose and a finger aren't congruent to any
circuit I know of.

That's a nice analogy too. It's nice to be able to go back and forth
'cause sometimes your brain is better as seeing things with a
different perspective. And by looking at where the analogies fail,
you can learn more about both systems.

Oh if the mechanical system has a damping term that doesn't go as the
velocity then you can get different behaviour. (Just like the water
analogy.)


Scroll down here till you get to damping, down near the bottom.

http://www.teachspin.com/instruments/tho/experiments.shtml

You can see friction damping, damping ~ velocity in the middle pic and
v^2 damping... only the middle one matches an RCL circuit.

The frictional damping is kinda interesting. The thing just stops at
some point and that point is *not* (in general) the equilibrium
position.

George H.

Right. I can't think of an electrical analogy to friction.

The old SU vacuum-piston carburetor, and the diaphragm carbs on my old
Honda motorcycles, provably had too much static friction to work. But
add a lot of engine vibration, and shazam, zero friction.

A weak analogy is ADC dithering.

John

 

[John Larkin]

On Tue, 11 Jan 2011 06:11:41 +0100, "F. Bertolazzi"
<TOGLIeset@MAIUSCOLEtdd.it> wrote:

Michael A. Terrell:

John Larkin wrote:

OK, what's the electrical equivalent of the finger-on-the-hose thing?
Schematic, please.

A transformer: High flow at low pressure is transformed into low
flow at high pressure.

Humm. Maybe John is right.

HA!

A transformer could be a water-powered motor driving a pump. For
non-steady-state, a driven piston pushing another piston of a
different size.

It's easier to just explain the electricity. That way, you don't have
to explain two systems, when you're trying to teach one.

One interesting analogy is a synchronous buck switcher to a pair of
gears. That sort of works. You can apply conservation of energy in
both ideal cases and predict behavior without having to go into gory
detail.

The holy grail of automotive design is the continuously-variable
transmission. The electronic equivalent is easy. Eat your hearts out,
MEs!

John