I hate imperial units

[John Larkin]

If you're really intent on it you can use SPICE to solve mechanical systems as
well... I remember spending one class years back going through the equations,
and somewhere around here I have the conversion charts.

I do remember being told that the main problem with simulating mechanical
systems like this is that real viscious dampers are horribly non-linear, even
springs aren't great, etc.

And there is no thermal inductor!

John

 

[redbelly]

Units of thermal conductivity: BTU*in/(ft^2*h*°F)

ugh

http://www.gordonengland.co.uk/conversion/thermcon.htm

Steel alloy (4140 like) is around 200, or around 30 in the more
sensible metric system units: W/(m*K)


Best regards,
Spehro Pefhany

Does kV/inch for dielectric strength drive you nuts too?

I have a problem with metric units being used exclusively in U.S.
science education. The reality is we have not converted, and won't be
anytime soon. It would be good to send a message to students that
science applies to everyday life, but for that it helps to use everyday
common units for science homework problems. At least assign a fraction
of homework using feet & pounds so it's more meaningful to American
students.

Mark

 

[Genome]

L is, of course, our inductance. B is the flux density and H is the
magnetising force. All of these sums use something called the SI system of
units which was worked out by the French because the British Imperial
system
is shit. Unfortunately the British landed the Americans with Imperial
units
so all their data sheets are messed up. The British noticed that the
French
system was better but could not admit it so they had to join the European
Community. Then the Belgians forced them to use it and, after a lot of
complaining, the British gave up and said OK neatly avoiding having to
give
the French credit for anything, and we still get to buy our potatoes in
pounds and ounces. Politics ay?

I have often wondered about the intransigence of Americans and Britons
when it comes to SI. If an alien race invaded Earth, they would see
immediately that we are a lazy race. We have spent millions on
publicity campaigns to convert, and nothing has changed really.

-Le Chaud Lapin-

Are you saying Aliens ain't lazy or political....(for extra bonus points on
their arrival) or are you putting yourself forward for chief negotiator?

DNA

 

[Joerg]

I have often wondered about the intransigence of Americans and Britons
when it comes to SI. If an alien race invaded Earth, they would see
immediately that we are a lazy race. We have spent millions on
publicity campaigns to convert, and nothing has changed really.

-Le Chaud Lapin-

Are you saying Aliens ain't lazy or political....

Only those aliens who are regularly participating in Usenet newsgroups
are political.

 

[Genome]

Only those aliens who are regularly participating in Usenet newsgroups are
political.

Are you trying to imply all three terms are mutually exclusive?

DNA

 

[Rich Grise]

And there is no thermal inductor!

What about the aluminum? Doesn't the heat flow lag the temperature input?

Thanks,
Rich

 

[Rich Grise]

If you need inches. If you need mm, it avoids a conversion and a
possible source of errors, especially when the numbers are oddball
sequences of digits and humans are involved.

That became glaringly obvious to me once, when I downloaded a CAD drawing
from SKF, to fit it into this thing I was detailing. Well, I just used the
"import" function, and when I imported this metric file into my inch file,
it showed up 25.4x size - the bearing was bigger than the whole machine!

So I scaled it by 0.03937, and it seemed to fit OK. ;-)

(A little OT for electronics, but everybody already knows I'm crazy, so
probably no harm done.) ;-)

Cheers!
Rich

 

[Rich Grise]

Does kV/inch for dielectric strength drive you nuts too?

I have a problem with metric units being used exclusively in U.S.
science education. The reality is we have not converted, and won't be
anytime soon. It would be good to send a message to students that
science applies to everyday life, but for that it helps to use everyday
common units for science homework problems. At least assign a fraction
of homework using feet & pounds so it's more meaningful to American
students.

Well, the "imperial" units are just plain more natural. Your thumb is an
inch (albeit, your little finger is a cm), and one foot is one foot! ;-)
And from outstreched fingertip to fingertip is 1 fathom, or 2 yards. ;-)

Cheers!
Rich

 

[Genome]

That became glaringly obvious to me once, when I downloaded a CAD drawing
from SKF, to fit it into this thing I was detailing. Well, I just used the
"import" function, and when I imported this metric file into my inch file,
it showed up 25.4x size - the bearing was bigger than the whole machine!

So I scaled it by 0.03937, and it seemed to fit OK. ;-)

(A little OT for electronics, but everybody already knows I'm crazy, so
probably no harm done.) ;-)

Cheers!
Rich

You should worry....... I might have learnt recently that 25.4mm is not an
exact inch.

However I suppose that with mechanical stuff things will bed themselves in
or you use the right grease with additives for the slopp.

DNA

 

[Eeyore]

I got used to non-metric units, except maybe when I lay tile where I
still use centimeters a lot for tiles with really complicated cuts.

When I see a tree I sometimes think out loud "Oh, that one would be
about 20,000,000 BTUs". Drives people crazy.

Hmm.... About 7,500kWh IIRC.

Graham

 

[Jonathan Kirwan]

Hmm.... About 7,500kWh IIRC.

Type:

20000000 BTU in kiloWatt*hour

into Google and you get,

20 000 000 BTU = 5 861.4214 kilowatt * hour

But even Google hates Spehro's:

1 BTU*inch/foot/foot/hour/Fahrenheit in Watt/meter/Kelvin

But it works if you do this:

1 BTU*inch/foot/foot/hour/(1 degree Fahrenheit) in Watt/meter/Kelvin

You get,

(1 ((((BTU * inch) / foot) / foot) / hour)) / (1 degree Fahrenheit) =
0.000313082877 (watt / meter) / Kelvin

Which without wanting to check, one can assume is probably about
right.

Jon

 

[Jonathan Kirwan]

But it works if you do this:

1 BTU*inch/foot/foot/hour/(1 degree Fahrenheit) in Watt/meter/Kelvin

Or the short-hand version:

1 BTU*in/ft/ft/hr/(1 F) in W/m/K

I think that's about as short as it gets.

Jon

 

[confused]

I have a problem with metric units being used exclusively in U.S.
science education. The reality is we have not converted, and won't be
anytime soon.

To be honest, that is one (more) thing about the U.S. of A. that surprises me.
While you have over the centuries appeared more than eager to throw off the
vestiges of your anglo antecedents, you cling to their antiquated weights and
measures system (incorporating some aberrations like gallons).

I grew up in the imperial system, faced conversion to metric-cgs in the early
60's and subsequently to metric-mks. In many areas I am now fluently
dimensionally tri-lingual - but I stll see people's height in imperial units.

It would be good to send a message to students that
science applies to everyday life, but for that it helps to use everyday
common units for science homework problems. At least assign a fraction
of homework using feet & pounds so it's more meaningful to American
students.

If the US is determined (has determined?) not to change to SI units "any time
soon", then certainly exposure to both systems is a must.

 

[Mike Monett]

Hmm. Well, let's us take those units out of the particular problem
domain they were designed for and try to figure out how many watts
it takes to maintain temperature difference of 10C (18F) across a
0.5" (12.7mm) piece of P20 steel 3/8" (9.52mm) thick. Convert
between W and BTU, between in or mm and square feet etc. Lots of
unnecessary work and possible places for errors.

Hello Speff,

You can eliminate most of the work and errors by using an equation
solver. Just enter the unit conversions, then solve for the desired
parameter.

This method is very fast and gives high confidence in the accuracy
of the results. I have tried different equations solvers but found
Roger Schafly's Mercury to be the best for this work.

Here's a simple example. Say we need to find out how many
barleycorns there are in pi furlongs.

Start by entering the unit conversions. (Note there is no direct
conversion between barleycorn and furlong.)

; Unit Conversion Factors

foot = yard * 3
furlong = yard / 202
inch = barleycorn / 3
inch = foot * 12
yard = fathom * 2

Now enter the desired parameter(s):

; Parameters

furlong = pi

The solution is:

barleycorn = 68536.985330715
fathom = 317.300858012569
foot = 1903.8051480754
furlong = 3.14159265358979
inch = 22845.6617769050
yard = 634.601716025138

(I simplified the printout to make it more readable.)

Now you can solve for any unknown. Just enter the desired parameter
and press solve. Unlike ordinary algebra solvers, you don't have to
rearrange the equation to put the unknown on the left side. This is
where many of the errors occur.

Once you have entered the necessary unit conversions, you don't have
to touch them again. This saves time and eliminates errors, since
you are re-using conversions that have already been debugged. You
can simply cut and paste from other files to add more units whenever
needed. Pretty soon you will have a library of conversions you can
draw on that will simplify and speed your work.

Roger Schafly's Mercury is free and available at

http://www.mindspring.com/~schlafly/eureka.htm

Hope this helps.

Regards,

Mike Monett

Antiviral, Antibacterial Silver Solution:
http://silversol.freewebpage.org/index.htm
SPICE Analysis of Crystal Oscillators:
http://silversol.freewebpage.org/spice/xtal/clapp.htm
Noise-Rejecting Wideband Sampler:
http://www3.sympatico.ca/add.automation/sampler/intro.htm

 

[Mike Monett]

Roger Schafly's Mercury is free and available at

http://www.mindspring.com/~schlafly/eureka.htm

Just to minimize confusion, Mercury is at

http://archives.math.utk.edu/software/msdos/calculus/mrcry209/.html

Roger also gives you an updated version of Eureka, which is the predecessor
to Mercury. That link is

http://www.mindspring.com/~schlafly/eureka-v211.zip

In most cases, either program can be used. It is good to have both programs
in the rare event when a file will run on one but not the other.

Regards,

Mike Monett

Antiviral, Antibacterial Silver Solution:
http://silversol.freewebpage.org/index.htm
SPICE Analysis of Crystal Oscillators:
http://silversol.freewebpage.org/spice/xtal/clapp.htm
Noise-Rejecting Wideband Sampler:
http://www3.sympatico.ca/add.automation/sampler/intro.htm

 

[krw]

What about the aluminum? Doesn't the heat flow lag the temperature input?

Of course not. Aluminum is a resistor/capacitor/low-pass filter
like any other material. A thermal inductor would have the
temperature lead the heat; rather a silly idea.

 

[krw]

You don't own one of those sliding pins thingies ? Wonderful for
transferring a door facing shape to a tile cut.

Hmm, I simply cut the molding back and don't sweat the silly
millimeters. That's what molding is for!

Really ?

My boiler is 125K BTU/hr, so I can easily scale from there. ;-)

 

[krw]

Jim Thompson wrote:


On Tue, 12 Dec 2006 17:37:34 GMT, Joerg



Spehro Pefhany wrote:



Units of thermal conductivity: BTU*in/(ft^2*h*°F)

ugh

http://www.gordonengland.co.uk/conversion/thermcon.htm

Steel alloy (4140 like) is around 200, or around 30 in the more
sensible metric system units: W/(m*K)



I got used to non-metric units, except maybe when I lay tile where I
still use centimeters a lot for tiles with really complicated cuts.


You don't own one of those sliding pins thingies ? Wonderful for
transferring a door facing shape to a tile cut.


Thought about it but then I always figured that after finishing this one
more room I'd be done tiling for the next 20-30 years. Wrong! I am
married, so...

What works really nicely is to cut several odd vellum templates. Those
can be angled at will and then fastened to each other with some masking
tape. The tape comes off with ease and you can re-use the templates for
all the other odd tiles to come. Until a splotch of mortar accidentally
lands on it, that is. However, every time it almost broke my heart not
having used that sheet for a nice high-tech super-gizmo schematic.

[ ... ]

I have been known to accurately measure the WHOLE house, then lay down
a hexagonal placement grid on the plan and slide it around for best
fit, with mostly near-1/2-tile cuts, and best look to the eye... with
fudging to accommodate a long hallway with almost an inch of TAPER :-(

Our neighbor is a civil engineer. Before he even thinks about firing up
the saw he does the whole project on AutoCad. Even if it's just the
guest bath. That drives his wife crazy because it can take a long time.

I did that for my bathrooms. It really doesn't take that long.
FOr the master bathroom I wanted to make sure the backer-board
didn't line up on either the subfloor joints or the floor joists.
I laid them all out in A9CAD, then laid the room outline on that.
It was a simple matter to lay the tile grid on that to find the
optimum starting point, which wasn't where I first expected. I had
nearly full tiles on three sides ("1/2 off two edges and those
under the base molding). Full tiles against the tub looked great,
since there "edge" on the tile.

If it's any consolation I also had to fudge the hallway. Did the kitchen
first and calculated it all so the 1/2-tile symmetries came out nicely.
I had no choice but to either compromise the kitchen or fudge the (long)
hallway because its end is almost 1/2" off track. Opted for making the
kitchen perfect because that's where everybody always hangs out.

Amazingly my house is perfectly square (just had it measured for
carpeting and was surprised how close he had to measure). THere is
one wall that is embarrassingly out of plumb though.

I did it the Sharpie way

Sharpies or wax pencils work. They do tend to wash off the glazed
surfaces though. I'm normally done cutting by then.

Fortunately I'm done tiling in this house. I just finished the
mantle (really a 3" thick concrete and marble tile slab) over the
wood stove. Gotta pack away the wet saw and the tools...

 

[Phil Hobbs]

Me? I do all my thermal stuff in SI units. What I hate is the way
people randomly use calories and joules/watts when specifying thermal
conductivity.

This is neat: you can use Spice to model thermal dynamics. Just
equate...

1 K/w == 1 ohm

1 K == 1 volt

1 gram aluminum == 1 farad

1 second == 1 second.

Works to about 5%

....for times long compared with the 2/3 power of the mass in grams.

That is neat, you're right.

Cheers,

Phil Hobbs

 

[Phil Hobbs]

Of course not. Aluminum is a resistor/capacitor/low-pass filter
like any other material. A thermal inductor would have the
temperature lead the heat; rather a silly idea.

Yep, no thermal inductors because the heat equation is first order in
time, so there are no imaginary exponential solutions.

Cheers,

Phil Hobbs