Understanding voltage

[Don Kelly]

----------------------------
"John Fields" <jfields@austininstruments.com> wrote in message
news:esh5e49meb8ev1v5p6q2889huo7ngipcjk@4ax.com...

On Tue, 30 Sep 2008 18:28:18 -0500, krw <krw@att.bizzzzzzzzzz> wrote:

In article <RfsEk.1952$ZP4.394@nlpi067.nbdc.sbc.com>,
Jon_Slaughter@Hotmail.com says...

"krw" <krw@att.bizzzzzzzzzz> wrote in message
news:MPG.234b62ace17ca7e698a24b@news.individual.net...
In article <gkhEk.2759$be.1230@nlpi061.nbdc.sbc.com>,
Jon_Slaughter@Hotmail.com says...
...
Nice job. Now he can go into fourth year.
No wonder our bridges are falling down.

When did one have to understand electricity to understand how to
build a
bridge?

Mechanical engineers don't build bridges either. They do build
automobiles and robots, though. Basic electricity would seem to be
a useful thing for MEs. Basic physics is rather useful, and
required, for EEs. MEs don't have to take the EM semester of
physics?


Ok... yes, I know that. Alhtough the overlap is much greater. Learning
about
your statics and dynamics is a major part of ME and CE'.

My response was specifically to the statement by Rose.

Understand. I was debating which one to respond to. ;-)

I'd rather the guy know squat about electricity and be a great bridge
builder than build shitty ass bridges cause he spent to much time
trying
to
learn about electricity for some school requirements to "broaden his
horizons". He could have spent that time more wisely.

Try a civil engineer if you want a bridge built. I'd rather my
civil engineer had the full load of physics too. We *are* talking
about basic electricity here.
Keith

True... but again, my statement was specifically about roses statement.

He/She is implying that if you don't know even the basics of electricity
then somehow you can't build a good bridge.

I don't think you should be an engineer without some knowledge of
basic physics. The fundamental units are rather important in all
engineering disciplines. I'm surely not an ME, but I know F=MA and
you can't push with a rope. ;-)

What I'm implying is that if the guy is an amazing bridge buildering(Ok,
I
know he's ME but Rose is the one who brought up the bridge building)
then
it's ok for him to suck as EE.

"Suck as an EE" <> "sucks at fundamental physics"

I'm sure Tesla sucked at ice hockey but I don't see anyone complaining
that
he should have spent more time on it. (What does ice hockey have to do
with
EE? Who knows but thats not the point)

Understandable. I didn't learn any ice hockey in college physics
either.

---
Not even anything about the interface between the blade and the ice and
how the blade was ground?

Pity...
---

Also we are getting off the point as if the guy is suppose to be the
best.
There are many EE's that don't even have a good understanding of their
own
craft so we should get onto those guys first.

The argument wasn't about whether or not there are EEs who shouldn't
be, rather whether it's understandable for an ME to lack basic
electrical knowledge. Would you think it OK for an EE to not know
that F=MA?

---
Not really, but on the electrical side of elementary physics we're
taught that:

F = MA

is the same as:

E = IR

Where E is a force exerted across a boundary,
I is the flow of mass across that boundary per unit time, and
R is the resistance to that flow.

---


Then I would say that you were taught incorrectly or incompletely.

Put it this way- a mass at constant velocity (as seen at a boundary)
requires a 0 force as there is no acceleration. A constant current (as you
say mass flow) in a resistance requires a voltage which is not 0. The
analogy breaks down immediately.

If you want a better analogy then consider force =current and voltage
=velocity and then mass =capacitance, spring =inductance and friction =
conductance. (nodal model)
You can also use a voltage=force and current =velocity analog and then mass=
inductance, spring =capacitance and friction = resistance. (loop model)
The nodal model is generally more useful.

The point is that friction is equivalent to resistance or conductance in
that it is lossy while mass and springs are storage elements equivalent to
capacitors and inductances.

Electrical engineers should know something about other branches of
engineering- enough to know when to call on others . They should also know
something about other branches of electrical engineering. That is know their
limits. This is also true of ME's CE's etc.

You have a far better knowledge of some areas of EE than I do. I cannot
advise you on electronics as that is not my thing, although I have had ,
fading with lack of use and upkeep, some basic knowledge in that area. Power
systems and machines are another matter (and both do require some ME and CE
knowledge because fields overlap).


--

Don Kelly dhky@shawcross.ca
remove the X to answer

JF

 

[Don Kelly]

----------------------------
"Rose" <couple7802002@yahoo.com> wrote in message
news:f5f3bef0-fb78-41a4-a34b-795b4ed7f15c@k7g2000hsd.googlegroups.com...
On Sep 30, 7:35 pm, John Fields <jfie...@austininstruments.com> wrote:

---
Not really, but on the electrical side of elementary physics we're
taught that:

F = MA

is the same as:

E = IR

Where E is a force exerted across a boundary,
I is the flow of mass across that boundary per unit time, and
R is the resistance to that flow.

JF

Congrats.. Somebody got it right.
Why didn't someone tell him to
understand Ohm's law?
----------------------
But it isn't right and saying it is right doesn't help.
--

Don Kelly dhky@shawcross.ca
remove the X to answer

 

[Salmon Egg]

In article <tbgFk.19406$kc.10826@newsfe12.iad>,
"Don Kelly" <dhky@shaw.ca> wrote:

If you want a better analogy then consider force =current and voltage
=velocity and then mass =capacitance, spring =inductance and friction =
conductance. (nodal model)
You can also use a voltage=force and current =velocity analog and then mass=
inductance, spring =capacitance and friction = resistance. (loop model)
The nodal model is generally more useful.

The point is that friction is equivalent to resistance or conductance in
that it is lossy while mass and springs are storage elements equivalent to
capacitors and inductances.

Although this analogy is valid and can be worked out mathematically, it
is the dual (in the circuit sense) of the analogy that is usually used.

Mechanical Electrical
Force Voltage
Speed Current
Mass Inductance
Compliance Capacitance
Windage Resistance Sliding friction is very different

This is the scheme used mostly by Olson. some of the analogous equations
are:
f=ma v=L(di/dt)
P=fs P=ei s is used for speed
KE=m*s^2/2 KE=L*i^2/2 magentic energy in an inductor.

This also leads to one of the most useful analogies that I have
used--impedance, especially characteristic impedance. For ac quantities.
Mechanical impedance = f/s and and Z=v/i. This concept is good for
levers, loudspeakers, gearboxes, transformers, etc.


Bill

--
Private Profit; Public Poop! Avoid collateral windfall!

 

[ValleyGirl]

On Thu, 02 Oct 2008 02:10:43 -0700, Salmon Egg <SalmonEgg@sbcglobal.net>
wrote:

In article <gbvjr0$ueg$3@gonzo>, Jasen Betts <jasen@xnet.co.nz> wrote:

Bridges are civil engineering aren't they?

Some are rocks--like the Wheatstone Bridge.

Bill

You're un-civil.

Well, your post was un-civil engineering, anyway.

 

[RoyLFuchs]

On Thu, 2 Oct 2008 20:19:53 -0700, "Don Kelly" <dhky@shaw.ca> wrote:

----------------------------
"John Fields" <jfields@austininstruments.com> wrote in message
news:esh5e49meb8ev1v5p6q2889huo7ngipcjk@4ax.com...
On Tue, 30 Sep 2008 18:28:18 -0500, krw <krw@att.bizzzzzzzzzz> wrote:

In article <RfsEk.1952$ZP4.394@nlpi067.nbdc.sbc.com>,
Jon_Slaughter@Hotmail.com says...

"krw" <krw@att.bizzzzzzzzzz> wrote in message
news:MPG.234b62ace17ca7e698a24b@news.individual.net...
In article <gkhEk.2759$be.1230@nlpi061.nbdc.sbc.com>,
Jon_Slaughter@Hotmail.com says...
...
Nice job. Now he can go into fourth year.
No wonder our bridges are falling down.

When did one have to understand electricity to understand how to
build a
bridge?

Mechanical engineers don't build bridges either. They do build
automobiles and robots, though. Basic electricity would seem to be
a useful thing for MEs. Basic physics is rather useful, and
required, for EEs. MEs don't have to take the EM semester of
physics?


Ok... yes, I know that. Alhtough the overlap is much greater. Learning
about
your statics and dynamics is a major part of ME and CE'.

My response was specifically to the statement by Rose.

Understand. I was debating which one to respond to. ;-)

I'd rather the guy know squat about electricity and be a great bridge
builder than build shitty ass bridges cause he spent to much time
trying
to
learn about electricity for some school requirements to "broaden his
horizons". He could have spent that time more wisely.

Try a civil engineer if you want a bridge built. I'd rather my
civil engineer had the full load of physics too. We *are* talking
about basic electricity here.
Keith

True... but again, my statement was specifically about roses statement.

He/She is implying that if you don't know even the basics of electricity
then somehow you can't build a good bridge.

I don't think you should be an engineer without some knowledge of
basic physics. The fundamental units are rather important in all
engineering disciplines. I'm surely not an ME, but I know F=MA and
you can't push with a rope. ;-)

What I'm implying is that if the guy is an amazing bridge buildering(Ok,
I
know he's ME but Rose is the one who brought up the bridge building)
then
it's ok for him to suck as EE.

"Suck as an EE" <> "sucks at fundamental physics"

I'm sure Tesla sucked at ice hockey but I don't see anyone complaining
that
he should have spent more time on it. (What does ice hockey have to do
with
EE? Who knows but thats not the point)

Understandable. I didn't learn any ice hockey in college physics
either.

---
Not even anything about the interface between the blade and the ice and
how the blade was ground?

Pity...
---

Also we are getting off the point as if the guy is suppose to be the
best.
There are many EE's that don't even have a good understanding of their
own
craft so we should get onto those guys first.

The argument wasn't about whether or not there are EEs who shouldn't
be, rather whether it's understandable for an ME to lack basic
electrical knowledge. Would you think it OK for an EE to not know
that F=MA?

---
Not really, but on the electrical side of elementary physics we're
taught that:

F = MA

is the same as:

E = IR

Where E is a force exerted across a boundary,
I is the flow of mass across that boundary per unit time, and
R is the resistance to that flow.

---


Then I would say that you were taught incorrectly or incompletely.

Put it this way- a mass at constant velocity (as seen at a boundary)
requires a 0 force as there is no acceleration. A constant current (as you
say mass flow) in a resistance requires a voltage which is not 0. The
analogy breaks down immediately.

If you want a better analogy then consider force =current and voltage
=velocity and then mass =capacitance, spring =inductance and friction =
conductance. (nodal model)
You can also use a voltage=force and current =velocity analog and then mass=
inductance, spring =capacitance and friction = resistance. (loop model)
The nodal model is generally more useful.

The point is that friction is equivalent to resistance or conductance in
that it is lossy while mass and springs are storage elements equivalent to
capacitors and inductances.

Electrical engineers should know something about other branches of
engineering- enough to know when to call on others . They should also know
something about other branches of electrical engineering. That is know their
limits. This is also true of ME's CE's etc.

You have a far better knowledge of some areas of EE than I do. I cannot
advise you on electronics as that is not my thing, although I have had ,
fading with lack of use and upkeep, some basic knowledge in that area. Power
systems and machines are another matter (and both do require some ME and CE
knowledge because fields overlap).

Howard Hughes proved that liquids are compressible.

Then, we all called him a genius, which he was.

Then, he crashed his toy (or it was sabotaged). Then, he went nuts.

 

[Salmon Egg]

In article <62hbe4p0p4ddj3qnj1i3trqjc33nlbi23o@4ax.com>,
ValleyGirl <LuvYerNailz@LikeIWouldGiveIt.Comeon> wrote:

On Thu, 02 Oct 2008 02:10:43 -0700, Salmon Egg <SalmonEgg@sbcglobal.net
wrote:

In article <gbvjr0$ueg$3@gonzo>, Jasen Betts <jasen@xnet.co.nz> wrote:

Bridges are civil engineering aren't they?

Some are rocks--like the Wheatstone Bridge.

Bill


You're un-civil.

Well, your post was un-civil engineering, anyway.

I don't remember. Maybe I was thinking of the Whitestone Bridge.

Bill

--
Private Profit; Public Poop! Avoid collateral windfall!

 

[Michael A. Terrell]

Don Kelly wrote:

----------------------------
"RoyLFuchs" <RoyLFuchs@urfargingicehole.org> wrote in message
news:jof5e4l3lqvq0m6afcopkrf1nafdsupl4l@4ax.com...
On Mon, 29 Sep 2008 23:02:58 -0700, Salmon Egg <SalmonEgg@sbcglobal.net
wrote:

I am no longer surprised.


As was stated earlier... your assessments here are worth exactly squat!

---
Actually, Salmon Egg knows more about electricity than most contributing to
this group. Do you have a problem with that?

Don't feed the dimbulb troll

--
http://improve-usenet.org/index.html

aioe.org, Goggle Groups, and Web TV users must request to be white
listed, or I will not see your messages.

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm


There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.

 

[John Larkin]

On Fri, 03 Oct 2008 00:06:46 -0700, ValleyGirl
<LuvYerNailz@LikeIWouldGiveIt.Comeon> wrote:

On Thu, 02 Oct 2008 02:10:43 -0700, Salmon Egg <SalmonEgg@sbcglobal.net
wrote:

In article <gbvjr0$ueg$3@gonzo>, Jasen Betts <jasen@xnet.co.nz> wrote:

Bridges are civil engineering aren't they?

Some are rocks--like the Wheatstone Bridge.

Bill


You're un-civil.

Well, your post was un-civil engineering, anyway.

My posts are electrical.

John

 

[John Fields]

On Fri, 03 Oct 2008 08:27:02 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 03 Oct 2008 00:06:46 -0700, ValleyGirl
LuvYerNailz@LikeIWouldGiveIt.Comeon> wrote:

On Thu, 02 Oct 2008 02:10:43 -0700, Salmon Egg <SalmonEgg@sbcglobal.net
wrote:

In article <gbvjr0$ueg$3@gonzo>, Jasen Betts <jasen@xnet.co.nz> wrote:

Bridges are civil engineering aren't they?

Some are rocks--like the Wheatstone Bridge.

Bill


You're un-civil.

Well, your post was un-civil engineering, anyway.


My posts are electrical.

---
Shocking!!!

JF

 

[John Larkin]

On Fri, 03 Oct 2008 11:13:02 -0500, John Fields
<jfields@austininstruments.com> wrote:

On Fri, 03 Oct 2008 08:27:02 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 03 Oct 2008 00:06:46 -0700, ValleyGirl
LuvYerNailz@LikeIWouldGiveIt.Comeon> wrote:

On Thu, 02 Oct 2008 02:10:43 -0700, Salmon Egg <SalmonEgg@sbcglobal.net
wrote:

In article <gbvjr0$ueg$3@gonzo>, Jasen Betts <jasen@xnet.co.nz> wrote:

Bridges are civil engineering aren't they?

Some are rocks--like the Wheatstone Bridge.

Bill


You're un-civil.

Well, your post was un-civil engineering, anyway.


My posts are electrical.

---
Shocking!!!

JF

Some posts are connected in parallel, and some posts are cereal.

John

 

[Michael A. Terrell]

John Larkin wrote:

On Fri, 03 Oct 2008 00:06:46 -0700, ValleyGirl
LuvYerNailz@LikeIWouldGiveIt.Comeon> wrote:

On Thu, 02 Oct 2008 02:10:43 -0700, Salmon Egg <SalmonEgg@sbcglobal.net
wrote:

In article <gbvjr0$ueg$3@gonzo>, Jasen Betts <jasen@xnet.co.nz> wrote:

Bridges are civil engineering aren't they?

Some are rocks--like the Wheatstone Bridge.

Bill


You're un-civil.

Well, your post was un-civil engineering, anyway.

My posts are electrical.

John

Dimbulb is finally showing herself for the Usenet pain slut she is.


--
http://improve-usenet.org/index.html

aioe.org, Goggle Groups, and Web TV users must request to be white
listed, or I will not see your messages.

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm


There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.

 

[John Fields]

On Fri, 03 Oct 2008 10:10:11 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 03 Oct 2008 11:13:02 -0500, John Fields
jfields@austininstruments.com> wrote:

On Fri, 03 Oct 2008 08:27:02 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 03 Oct 2008 00:06:46 -0700, ValleyGirl
LuvYerNailz@LikeIWouldGiveIt.Comeon> wrote:

On Thu, 02 Oct 2008 02:10:43 -0700, Salmon Egg <SalmonEgg@sbcglobal.net
wrote:

In article <gbvjr0$ueg$3@gonzo>, Jasen Betts <jasen@xnet.co.nz> wrote:

Bridges are civil engineering aren't they?

Some are rocks--like the Wheatstone Bridge.

Bill


You're un-civil.

Well, your post was un-civil engineering, anyway.


My posts are electrical.

---
Shocking!!!

JF

Some posts are connected in parallel, and some posts are cereal.

---
Cereal posts? That doesn't make a grain of sense.

JF

 

[krw]

In article <kr2de4lljr9s5fj9th7l1abmb6k4taubh7@4ax.com>,
jfields@austininstruments.com says...

On Fri, 03 Oct 2008 10:10:11 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 03 Oct 2008 11:13:02 -0500, John Fields
jfields@austininstruments.com> wrote:

On Fri, 03 Oct 2008 08:27:02 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 03 Oct 2008 00:06:46 -0700, ValleyGirl
LuvYerNailz@LikeIWouldGiveIt.Comeon> wrote:

On Thu, 02 Oct 2008 02:10:43 -0700, Salmon Egg <SalmonEgg@sbcglobal.net
wrote:

In article <gbvjr0$ueg$3@gonzo>, Jasen Betts <jasen@xnet.co.nz> wrote:

Bridges are civil engineering aren't they?

Some are rocks--like the Wheatstone Bridge.

Bill


You're un-civil.

Well, your post was un-civil engineering, anyway.


My posts are electrical.

---
Shocking!!!

JF

Some posts are connected in parallel, and some posts are cereal.

---
Cereal posts? That doesn't make a grain of sense.

Back to the wheatstone bridge?

--
Keith

 

[Michael A. Terrell]

John Fields wrote:

Cereal posts? That doesn't make a grain of sense.

http://static.flickr.com/68/186536545_20024adcac_o.jpg


--
http://improve-usenet.org/index.html

aioe.org, Goggle Groups, and Web TV users must request to be white
listed, or I will not see your messages.

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm


There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.

 

[ValleyGirl]

On Fri, 03 Oct 2008 05:41:32 -0700, Salmon Egg <SalmonEgg@sbcglobal.net>
wrote:

In article <62hbe4p0p4ddj3qnj1i3trqjc33nlbi23o@4ax.com>,
ValleyGirl <LuvYerNailz@LikeIWouldGiveIt.Comeon> wrote:

On Thu, 02 Oct 2008 02:10:43 -0700, Salmon Egg <SalmonEgg@sbcglobal.net
wrote:

In article <gbvjr0$ueg$3@gonzo>, Jasen Betts <jasen@xnet.co.nz> wrote:

Bridges are civil engineering aren't they?

Some are rocks--like the Wheatstone Bridge.

Bill


You're un-civil.

Well, your post was un-civil engineering, anyway.

I don't remember. Maybe I was thinking of the Whitestone Bridge.

Bill

http://www.redrivergorgearches.com/


Volume 1, White's Branch Arch

 

[RoyLFuchs]

On Fri, 03 Oct 2008 09:58:25 -0400, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

Don Kelly wrote:

----------------------------
"RoyLFuchs" <RoyLFuchs@urfargingicehole.org> wrote in message
news:jof5e4l3lqvq0m6afcopkrf1nafdsupl4l@4ax.com...
On Mon, 29 Sep 2008 23:02:58 -0700, Salmon Egg <SalmonEgg@sbcglobal.net
wrote:

I am no longer surprised.


As was stated earlier... your assessments here are worth exactly squat!

---
Actually, Salmon Egg knows more about electricity than most contributing to
this group. Do you have a problem with that?


Don't feed the dimbulb troll

I did not respond to his stupidity, idiot. I will, however, point out
yours.

 

[John Larkin]

On Fri, 03 Oct 2008 16:11:13 -0700, RoyLFuchs
<RoyLFuchs@urfargingicehole.org> wrote:

On Fri, 03 Oct 2008 08:25:45 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 03 Oct 2008 01:10:59 -0700, RoyLFuchs
RoyLFuchs@urfargingicehole.org> wrote:




Howard Hughes proved that liquids are compressible.


Right. Prior to that, nobody noticed that sound propagates in water.

It also propagates through solids, idiot. Sound propagation has
nothing to do with compressibility.

Wonderful! You are raising being really, really wrong to a high art.

Here, this may help:

http://en.wikipedia.org/wiki/Speed_of_sound#General_formulae

http://hyperphysics.phy-astr.gsu.edu/Hbase/sound/souspe2.html

See? The speed is inverse on compressibility. That was known a long
time before HH was born.

Then, we all called him a genius, which he was.

Then, he crashed his toy (or it was sabotaged). Then, he went nuts.


C'mon Roy, explain voltage to us.

Take a small rooftop lightning rod, and an ankle chain. Walk up on a
tall 14k' plus mountain.. Hold the lightning rod up.

You'll learn what voltage and current is, but it will be the last thing
you learn.

You don't understand voltage, do you? Don't feel bad, lots of techs
don't actually understand voltage. I suppose I'll have to explain it
one of these days.

John

 

[Michael A. Terrell]

John Larkin wrote:

On Fri, 03 Oct 2008 16:11:13 -0700, RoyLFuchs
RoyLFuchs@urfargingicehole.org> wrote:

On Fri, 03 Oct 2008 08:25:45 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 03 Oct 2008 01:10:59 -0700, RoyLFuchs
RoyLFuchs@urfargingicehole.org> wrote:




Howard Hughes proved that liquids are compressible.


Right. Prior to that, nobody noticed that sound propagates in water.

It also propagates through solids, idiot. Sound propagation has
nothing to do with compressibility.

Wonderful! You are raising being really, really wrong to a high art.

Here, this may help:

http://en.wikipedia.org/wiki/Speed_of_sound#General_formulae

http://hyperphysics.phy-astr.gsu.edu/Hbase/sound/souspe2.html

See? The speed is inverse on compressibility. That was known a long
time before HH was born.


Then, we all called him a genius, which he was.

Then, he crashed his toy (or it was sabotaged). Then, he went nuts.


C'mon Roy, explain voltage to us.

Take a small rooftop lightning rod, and an ankle chain. Walk up on a
tall 14k' plus mountain.. Hold the lightning rod up.

You'll learn what voltage and current is, but it will be the last thing
you learn.

You don't understand voltage, do you? Don't feel bad, lots of techs
don't actually understand voltage. I suppose I'll have to explain it
one of these days.

You'll have to use small words and type real slow, for dimbulb.


--
http://improve-usenet.org/index.html

aioe.org, Goggle Groups, and Web TV users must request to be white
listed, or I will not see your messages.

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm


There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.

 

[Don Kelly]

----------------------------
"Salmon Egg" <SalmonEgg@sbcglobal.net> wrote in message
news:SalmonEgg-560BC8.22085902102008@news.la.sbcglobal.net...

In article <tbgFk.19406$kc.10826@newsfe12.iad>,
"Don Kelly" <dhky@shaw.ca> wrote:

If you want a better analogy then consider force =current and voltage
=velocity and then mass =capacitance, spring =inductance and friction =
conductance. (nodal model)
You can also use a voltage=force and current =velocity analog and then
mass=
inductance, spring =capacitance and friction = resistance. (loop model)
The nodal model is generally more useful.

The point is that friction is equivalent to resistance or conductance in
that it is lossy while mass and springs are storage elements equivalent
to
capacitors and inductances.

Although this analogy is valid and can be worked out mathematically, it
is the dual (in the circuit sense) of the analogy that is usually used.

Mechanical Electrical
Force Voltage
Speed Current
Mass Inductance
Compliance Capacitance
Windage Resistance Sliding friction is very different

This is the scheme used mostly by Olson. some of the analogous equations
are:
f=ma v=L(di/dt)
P=fs P=ei s is used for speed
KE=m*s^2/2 KE=L*i^2/2 magentic energy in an inductor.

This also leads to one of the most useful analogies that I have
used--impedance, especially characteristic impedance. For ac quantities.
Mechanical impedance = f/s and and Z=v/i. This concept is good for
levers, loudspeakers, gearboxes, transformers, etc.


Bill
--------------------

Looking at it from a machines viewpoint, the nodal analogy is, in my mind,
having used both, actually better than the loop analogy.
force----current
voltage----velocity
capacitance-----mass
inductance----spring compliance
conductance----resistance

Note that for gears the speed is proportional to the gear ratio and the
torque is inversely proportional which corresponds to voltage and current
respectively for a transformer. This is true for a lever as well. These are
inverted in the loop analog but the impedance, as you note, is inverted in
the nodal analog.
In a motor the torque is current dependent and the voltage is related to
speed. One also notes that the inertial mass of a spinning armature nicely
reflects back to the electrical side as a capacitor. This analogue also more
closely matches the mechanical block diagrams for multimass cases and in
such cases, the nodal approach does offer some computational advantage (just
as in a power system load flow or even fault analysis a nodal approach is
used- simpler in that there is no need to choose loops and node choice is
automatic- an admittance array is a turn the crank algorithm with no
"choosing" of a base tree and branches so it is much easier to program the
idiot box).

Berenak in "Acoustics" introduces both models but tends to the loop or
impedance model but others in this area have used the nodal or mobility
model.

What it boils down to is that the choice is really the user's preference
(and such preferences are based on what one's background happens to be ).


--

Don Kelly dhky@shawcross.ca
remove the X to answer

 

[John Larkin]

On Sat, 04 Oct 2008 12:49:53 -0700, RoyLFuchs
<RoyLFuchs@urfargingicehole.org> wrote:

On Fri, 03 Oct 2008 19:37:20 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 03 Oct 2008 16:11:13 -0700, RoyLFuchs
RoyLFuchs@urfargingicehole.org> wrote:

On Fri, 03 Oct 2008 08:25:45 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 03 Oct 2008 01:10:59 -0700, RoyLFuchs
RoyLFuchs@urfargingicehole.org> wrote:




Howard Hughes proved that liquids are compressible.


Right. Prior to that, nobody noticed that sound propagates in water.

It also propagates through solids, idiot. Sound propagation has
nothing to do with compressibility.


Wonderful! You are raising being really, really wrong to a high art.

Here, this may help:

http://en.wikipedia.org/wiki/Speed_of_sound#General_formulae

http://hyperphysics.phy-astr.gsu.edu/Hbase/sound/souspe2.html

See? The speed is inverse on compressibility. That was known a long
time before HH was born.


Wrong. You speak of liquids and gasses.

I mentioned neither.

In solids it relates to shear
deformation at the lattice level. Nothing is compressed. No physical
shape change occurs

Of course the material is compressed as a sound wave passes... any
sound wave, longitudinal or transverse. "Deformation at the lattice
level" is big words for compression and stretching.

Always Wrong, a perfect record! You couldn't be this wrong by
accident... you've got to be doing it on purpose. The pain slut thing,
I suppose.

In the wiki link, you should examine the portion on speed through
solids, as most of the article is about speed through, and effects on
gasses and liquids. Solids barely get a mention.

The subject, as you introduced it, was compressibility of *liquids*.
My point was that the equation for sound velocity was known long
before Howard Hughes was born, and one of the terms is
compressibility, and people have known that sound travels in water
since people learned to swim.

Git a reference for the Howard Hughes claim?

You probably believe that glass is a solid, and you probably think that
two colliding spheres is only a momentary collision.

A mind reader too?


John