water analogy- a simple calculator

[F. Bertolazzi]

John Larkin:

On Wed, 12 Jan 2011 01:46:59 +0100, "F. Bertolazzi"
TOGLIeset@MAIUSCOLEtdd.it> wrote:

John Larkin:

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

Uh?

Uh? Can you?

Yes, I can. But I understand that somebody that cites non-laminar flows in
example pipes just to demonstrate that he is right no matter what, will
surely pull my "chain" with static and dynamic friction.

Wait until I get to retirement age and you'll see. ;-)

 

[Jamie]

John Larkin wrote:

On Tue, 11 Jan 2011 21:27:19 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:


Rich Grise wrote:


John Larkin wrote:


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


This is a joke, right?

Personally, I don't see what a dashpot does, but damp (much like a
snubber). The only analog to an inductor I can think of would be
a positive-displacement turbine (like a gear pump) and a flywheel.

Thanks!
Rich


Eddy current?
Drop a PM down a non-magnetic conductible tube and see it drop
slowly.


Jamie


Friction results in zero motion until some threshold amount of force
is applied. And sliding friction drag mostly depends on normal force
but not velocity. I don't know of any electrical phenom that behaves
like that.

The PM in the tube thing is more like viscoscity; no force threshold
for motion, and drag increases with velocity.

John

Yes, a free drop is viscosity effects, if you want to put it that way.

pulling on it, to increase velocity will also increase drag, hence eddy
current clutches, brakes, dashpots etc., that generate more drag as
velocity increases.


Breaking threshold in comparison, would be a PM suck to something
requiring minimum tension to move across a magnetic surface, or a
solenoid, minimum surface breaking tension.

Maybe we're talking about something else here.

Jamie

 

[Rich Grise]

Phil Hobbs wrote:

Rich Grise wrote:
John Larkin wrote:

A true anology uses the same equations, with the same solutions.

No, that's an identity.

An analogy is like, "time flies like an arrow." ;-)

"And fruit flies like a banana."

(http://preview.tinyurl.com/27jchnw)

Use this stop watch to see how long it takes the flies to make it

around the race track, and do so with great alacrity! ;-)

Cheers!
Rich

 

[F. Bertolazzi]

John Larkin:

Of course most people will forget the basic lessons if they don't use
it regularly. But then, they may as well. No point cluttering your
brain with stuff you don't intend to use. They made me study French,
which I forgot as soon as I could.

A very nice definition of culture is "everything you know after you forgot
everything".

I've been at grammar school, studying Greek and Latin for five years,
French only for two (plus the three already done in middle school) and,
guess what, I learned English by listening to the Beatles. Despite of that,
after few months in the US, I scored better, in verbal ability, that 75% of
the other GRE candidates. And I can still survive in France.

The point of introductory EE is to get people doing the math from the
very start. Because they will be helpless if they can't do the math.

Clearly. But they would be in much worse shape if they did not understand
the "hose thing" before starting to make otherwise meaningless
calculations.

As I mentioned before, the water analogy should be taught in secondary
schools, not university. But, on the first lesson of EE 101, I'd make sure
everybody is familiar with it.

Analogies don't help there.

Analogies are fundamental to get you there. After, you can forget them.

 

[John Fields]

On Tue, 11 Jan 2011 13:47:18 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

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

---
Why would you think that resistance isn't analogous to friction?

---
JF

 

[F. Bertolazzi]

John Fields:

On Tue, 11 Jan 2011 13:47:18 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

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

---
Why would you think that resistance isn't analogous to friction?

Because he does not want to. ;-)

 

[Bob Masta]

On Tue, 11 Jan 2011 17:35:43 -0800, Rich Grise
<richg@example.net.invalid> wrote:

The only analog to an inductor I can think of would be
a positive-displacement turbine (like a gear pump) and a flywheel.

How about a big coiled garden hose? Not only looks like an
inductor, but the mass of the water in it will give it
inductor properties: Hard to get current to start flowing,
and once it's flowing, hard to stop or change directions.

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
Pitch Track, Pitch-to-MIDI
Science with your sound card!

 

[Bob Masta]

On Tue, 11 Jan 2011 13:41:39 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

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

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!

They need analogies so they know what equations to borrow
from the EEs!

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
Pitch Track, Pitch-to-MIDI
Science with your sound card!

 

[F. Bertolazzi]

Bob Masta:

On Tue, 11 Jan 2011 17:35:43 -0800, Rich Grise
richg@example.net.invalid> wrote:

The only analog to an inductor I can think of would be
a positive-displacement turbine (like a gear pump) and a flywheel.

How about a big coiled garden hose?

HA! [cit.]

The All-Encompassing Garden Hose Analogy!

BTW, what about shorter hoses? Short conductors don't have any inductance,
nor capacity (as the hose's elasticity)?

This reminds me that a pipe can also oscillate and transform hydraulic
energy into acoustic waves (as in badly done house piping), pretty much
like an antenna transfers energy in another domain.

 

[John Larkin]

On Wed, 12 Jan 2011 13:31:45 GMT, N0Spam@daqarta.com (Bob Masta)
wrote:

On Tue, 11 Jan 2011 13:41:39 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

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

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!


They need analogies so they know what equations to borrow
from the EEs!

Working with MEs can be fun. Once we had a requirement to furnish a
mechanical propeller shaft-rotation counter for a big ship. It was to
be a non-resettable veeder-root type indicator, in a sealed box with a
window for readout of the counts. It had to count turns in either
direction, since the ship runs in reverse now and then. The MEs were
stumped, so I invented the mechanical full-wave rectifier. It was
simple, a couple of gears and belts and two of those one-way clutch
things, essentially an inverter and two diodes. I was surprised they
hadn't thought of that.

I've run into similar situations with various scientists and such.
Electronic design teaches us all sorts of topological and algorithmic
and signal processing tricks that do have useful analogies in other
domains.

John

 

[John Larkin]

On Wed, 12 Jan 2011 13:30:11 GMT, N0Spam@daqarta.com (Bob Masta)
wrote:

On Tue, 11 Jan 2011 17:35:43 -0800, Rich Grise
richg@example.net.invalid> wrote:

The only analog to an inductor I can think of would be
a positive-displacement turbine (like a gear pump) and a flywheel.

How about a big coiled garden hose? Not only looks like an
inductor, but the mass of the water in it will give it
inductor properties: Hard to get current to start flowing,
and once it's flowing, hard to stop or change directions.

Hydraulic accumulator? That's a pretty lossy inductor equivalent.

John

 

[John Larkin]

On Wed, 12 Jan 2011 06:16:37 -0600, John Fields
<jfields@austininstruments.com> wrote:

On Tue, 11 Jan 2011 13:47:18 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

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

---
Why would you think that resistance isn't analogous to friction?

---
JF

Grossly different behavior, explained elsewhere. Resistance is more
like low-Reynolds number viscoscity.

The only things that resistance and friction have in common is that
both are dissipative.

John

 

[John Larkin]

On Wed, 12 Jan 2011 13:25:14 +0100, "F. Bertolazzi"
<TOGLIeset@MAIUSCOLEtdd.it> wrote:

John Fields:

On Tue, 11 Jan 2011 13:47:18 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

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

---
Why would you think that resistance isn't analogous to friction?

Because he does not want to. ;-)

I don't want to because the behaviors are very different. You'd have
to actually understand friction behavior to see why. Neither static
friction nor sliding friction behave like electrical resistance.

John

 

[F. Bertolazzi]

John Larkin:

I don't want to because the behaviors are very different. You'd have
to actually understand friction behavior to see why. Neither static
friction nor sliding friction behave like electrical resistance.

What about the air drag of "your" mass hung to a spring?

You know, there are several kinds of friction, most of them due to...
electromagnetic forces.

 

[George Herold]

On Jan 11, 4:55 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 11 Jan 2011 06:11:41 +0100, "F. Bertolazzi"

TOGLIe...@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.

Oh the piston thing works nicely for me as a transformer. Thanks.

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!

Did you ever see the variable Vee Belt drive on a snowmobile?
George H.

John

 

[Michael A. Terrell]

Bob Masta wrote:

On Tue, 11 Jan 2011 17:35:43 -0800, Rich Grise
richg@example.net.invalid> wrote:

The only analog to an inductor I can think of would be
a positive-displacement turbine (like a gear pump) and a flywheel.

How about a big coiled garden hose? Not only looks like an
inductor, but the mass of the water in it will give it
inductor properties: Hard to get current to start flowing,
and once it's flowing, hard to stop or change directions.

No 'Mutual Inductance' though.


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

 

[George Herold]

On Jan 11, 9:49 pm, "F. Bertolazzi" <TOGLIe...@MAIUSCOLEtdd.it> wrote:

John Larkin:

On Wed, 12 Jan 2011 01:46:59 +0100, "F. Bertolazzi"
TOGLIe...@MAIUSCOLEtdd.it> wrote:

John Larkin:

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

Uh?

Uh? Can you?

Yes, I can. But I understand that somebody that cites non-laminar flows in
example pipes just to demonstrate that he is right no matter what, will
surely pull my "chain" with static and dynamic friction.

Wait until I get to retirement age and you'll see. ;-)

Friction is different than a resistor. (Did you look at the plots I
posted?) With friction you get a decay in amplitude that is linear in
time. As long as the oscillator is moving it's losing amplitude at a
constant rate. For a damping term that depends on velocity you get an
exponential decay. Like an RCL circuit.

With electricity the electrons start moving even with the smallest
electric field.

I've been racking my brains for a friction analogy in electronics and
can think of nothing. Now I'm wondering if you could make some circit
that would look "friction like". (An oscillator that decays
linearly.)

George H.

 

[George Herold]

On Jan 12, 7:16 am, John Fields <jfie...@austininstruments.com> wrote:

On Tue, 11 Jan 2011 13:47:18 -0800, John Larkin

jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

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

---
Why would you think that resistance isn't analogous to friction?

---
JF

Did you look at the plots I posted John? Friction causes a linear
decrease in amplitude, not exponential.

George H.

 

[John Larkin]

On Wed, 12 Jan 2011 10:38:47 -0800 (PST), George Herold
<ggherold@gmail.com> wrote:

On Jan 11, 9:49 pm, "F. Bertolazzi" <TOGLIe...@MAIUSCOLEtdd.it> wrote:
John Larkin:

On Wed, 12 Jan 2011 01:46:59 +0100, "F. Bertolazzi"
TOGLIe...@MAIUSCOLEtdd.it> wrote:

John Larkin:

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

Uh?

Uh? Can you?

Yes, I can. But I understand that somebody that cites non-laminar flows in
example pipes just to demonstrate that he is right no matter what, will
surely pull my "chain" with static and dynamic friction.

Wait until I get to retirement age and you'll see. ;-)

Friction is different than a resistor. (Did you look at the plots I
posted?) With friction you get a decay in amplitude that is linear in
time. As long as the oscillator is moving it's losing amplitude at a
constant rate. For a damping term that depends on velocity you get an
exponential decay. Like an RCL circuit.

With electricity the electrons start moving even with the smallest
electric field.

I've been racking my brains for a friction analogy in electronics and
can think of nothing. Now I'm wondering if you could make some circit
that would look "friction like". (An oscillator that decays
linearly.)

And then just stops.

John

 

[John Larkin]

On Wed, 12 Jan 2011 18:47:23 +0100, "F. Bertolazzi"
<TOGLIeset@MAIUSCOLEtdd.it> wrote:

John Larkin:

I don't want to because the behaviors are very different. You'd have
to actually understand friction behavior to see why. Neither static
friction nor sliding friction behave like electrical resistance.

What about the air drag of "your" mass hung to a spring?

You know, there are several kinds of friction, most of them due to...
electromagnetic forces.

Now you're parsing definitions. I don't consider viscous force to be
"friction." Maybe you do. If you do, then some forms of friction
behave like electrical resistance and some don't. Enjoy.

John