ZeroExperience
Aerospace
As title asks.
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Do you want to switch to SI units? 8
- Thread starter ZeroExperience
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JohnRBaker
Mechanical
David, you mentioned 18 wheelers...
Well speaking of 'wheels', the 'rims' are designed and sized based on Imperial/English untis while the 'tires' are Metric.
And every mass produced automotive sparkplug ever manufactured was Metric, even 60 years ago when every other nut and bolt on an American-built car or truck was Imperial/English units (why do you think sets of SAE wrenches always came with special sockets designated for 'Sparkplugs').
But on the other hand, fire-hydrants and the standard for firehose connections are based on Imperial/English units. Sometimes absolute assurance of interchangeability is more important than complying with the local units of measure.
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
UG/NX Museum:
To an Engineer, the glass is twice as big as it needs to be.
Well speaking of 'wheels', the 'rims' are designed and sized based on Imperial/English untis while the 'tires' are Metric.
And every mass produced automotive sparkplug ever manufactured was Metric, even 60 years ago when every other nut and bolt on an American-built car or truck was Imperial/English units (why do you think sets of SAE wrenches always came with special sockets designated for 'Sparkplugs').
But on the other hand, fire-hydrants and the standard for firehose connections are based on Imperial/English units. Sometimes absolute assurance of interchangeability is more important than complying with the local units of measure.
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
UG/NX Museum:
To an Engineer, the glass is twice as big as it needs to be.
SomptingGuy
Automotive
SI unifies electrical, mechanical and thermal analysis with no nasty conversion factors. So easy to simulate whole systems using it. You have to cope with rad/s for shaft speeds, but that's not a difficult leap to make.
Ask me what I weigh in kg though, and I'd need to think about it.
- Steve
Ask me what I weigh in kg though, and I'd need to think about it.
- Steve
moltenmetal
Chemical
I need to do my calcs in SI to avoid forgetting a g sub c somewhere. What the )(*$ kind of unit system doesn't even allow you to calculate F = m*a without using a conversion factor?
I then convert the results to a unit my commonsense is calibrated in.
We work in THREE systems here: SI and derived metric units, US customary units, and Imperial units.
I then convert the results to a unit my commonsense is calibrated in.
We work in THREE systems here: SI and derived metric units, US customary units, and Imperial units.
SomptingGuy
Automotive
We were taught that F was proportional to m*a in physics classes at the age of about 13 and did loads of experiments to demonstrate it. A big light switched on in my brain when I finally realised that in SI units, not only was F proportional to m*a, it was actually equal to it.
- Steve
- Steve
ornerynorsk
Industrial
Who's up for several of 5.7 deciliters of Guinness??? Nope, just doesn't sound right!
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
A rose by any other name Ornery...
Posting guidelines faq731-376 (probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484
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patprimmer
New member
It doesn't, hence the use of terms like a litre of milk but a pint of beer.
I still like to use psi or bar for pressure. I don't even know what the tables are that David refers to. Boiling point vs pressure maybe? I like psi because I can envisage it graphically in my mind and I am accustomed to it's effect on tyres. I like bar because it is a simple multiplier of atmospheric pressure for forced induction engines.
If we used deg K instead of C I guess temperature changes in gasses from pressurisation would become a bit easier.
This could go all year though.
Ultimately we use what we have at hand and learn the conversions if really necessary.
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
I still like to use psi or bar for pressure. I don't even know what the tables are that David refers to. Boiling point vs pressure maybe? I like psi because I can envisage it graphically in my mind and I am accustomed to it's effect on tyres. I like bar because it is a simple multiplier of atmospheric pressure for forced induction engines.
If we used deg K instead of C I guess temperature changes in gasses from pressurisation would become a bit easier.
This could go all year though.
Ultimately we use what we have at hand and learn the conversions if really necessary.
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
Pat,
I'm talking about classroom materials. Things like the units that an empirical equation needs in fps in one column and the units in SI in another, or a tablulation of a physiscal parameter like saturation quantity of water in natural gas vs. pressure for a constant temperature.
Your bar example works in a lot of the world, but I always find myself in places where local atmophperic pressure is 0.7 bar(a) or less and using bar doesn't help the math much.
David
I'm talking about classroom materials. Things like the units that an empirical equation needs in fps in one column and the units in SI in another, or a tablulation of a physiscal parameter like saturation quantity of water in natural gas vs. pressure for a constant temperature.
Your bar example works in a lot of the world, but I always find myself in places where local atmophperic pressure is 0.7 bar(a) or less and using bar doesn't help the math much.
David
GregLocock
Automotive
"Ask me what I weigh in kg though, and I'd need to think about it."
Well first you'd need to find out which planet you are on.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376
Well first you'd need to find out which planet you are on.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376
Ah, the joy of mass V weight pedantry.;-)
Posting guidelines faq731-376 (probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484
What is Engineering anyway: faq1088-1484
SomptingGuy
Automotive
Ornery:
Who's up for approximately four fifths of a pint of Guinness?
- Steve
Who's up for approximately four fifths of a pint of Guinness?
- Steve
Darn 16 oz colonial pint.
Posting guidelines faq731-376 (probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484
What is Engineering anyway: faq1088-1484
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3
- #36
If it's a question of what you like to use, it's what you are comfortable with. If it's a question of what's a better system then lets look at some comparisons.
Temperature:
C - 0 is the freezing point of water, 100 is the boiling point. Relatable and useful in many scientific and industrial settings.
F - 0 means...ahh...the coldest temperature they could achieve at the time. 100 means....ahh...the internal temperature of the human body...wait, we got that wrong.
Length:
m - Base 10. Enough said.
ft - 3'7-1/2" + 4'3-5/8" + 6'5-1/4" + 8'7" = need to convert into either inches or feet before I plug into my calculator.
Force:
N - Not as relatable as lbf unless you use them.
lbf - Not to be confused with lbm...or are they interchangable...and what about that slug thing? Do I need to multiply or divide by gravity to get to it?
Volume:
m^3 - yes, L are commonly used for liquid but you just need to move the decimal point around.
Oz - fluid volume (8 oz per cup), dry volume(wait...oz don't exists for dry volume). And don't forget weight (16 oz per pound). Don't like oz, ok gallons...wait US or Imperial. Don't like gallons, ok ft^3....now what's the conversion.
Scalability:
Metric - change the prefix, move the decimal.
Imperial - use a completely different unit of measure, find what wacky conversion is required and calculate.
Temperature:
C - 0 is the freezing point of water, 100 is the boiling point. Relatable and useful in many scientific and industrial settings.
F - 0 means...ahh...the coldest temperature they could achieve at the time. 100 means....ahh...the internal temperature of the human body...wait, we got that wrong.
Length:
m - Base 10. Enough said.
ft - 3'7-1/2" + 4'3-5/8" + 6'5-1/4" + 8'7" = need to convert into either inches or feet before I plug into my calculator.
Force:
N - Not as relatable as lbf unless you use them.
lbf - Not to be confused with lbm...or are they interchangable...and what about that slug thing? Do I need to multiply or divide by gravity to get to it?
Volume:
m^3 - yes, L are commonly used for liquid but you just need to move the decimal point around.
Oz - fluid volume (8 oz per cup), dry volume(wait...oz don't exists for dry volume). And don't forget weight (16 oz per pound). Don't like oz, ok gallons...wait US or Imperial. Don't like gallons, ok ft^3....now what's the conversion.
Scalability:
Metric - change the prefix, move the decimal.
Imperial - use a completely different unit of measure, find what wacky conversion is required and calculate.
JohnRBaker
Mechanical
Or you could just download something like 'Versaverter' (a free program found at: ).
I've been using 'Versaverter 1' since about 2000 and it works great.
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
UG/NX Museum:
To an Engineer, the glass is twice as big as it needs to be.
I've been using 'Versaverter 1' since about 2000 and it works great.
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
UG/NX Museum:
To an Engineer, the glass is twice as big as it needs to be.
MiketheEngineer
Structural
Yes - much easier to use and to computer program!!
When they built the new Federal Building here in St. Louis - all the dimensions were metric.
Guess what - they had to go out and buy like $25,000 worth of dual marked tape measures for the Missouri farm boys building it.
Also, Canada is supposedly "metric" - but I get orders all the time for parts that 254 mm long (10'') Go figure!!
When they built the new Federal Building here in St. Louis - all the dimensions were metric.
Guess what - they had to go out and buy like $25,000 worth of dual marked tape measures for the Missouri farm boys building it.
Also, Canada is supposedly "metric" - but I get orders all the time for parts that 254 mm long (10'') Go figure!!
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1
- #39
Really, the ONLY advantage Imperial has over Metric, is that people are more familiar with it. If it was the other way around and Metric was here first and someone was trying to promote a switch to Imperial with all its odd conversions we wouldn't be having this conversation.
I am fairly young and I can't easily visualize metric (I need to do the math to give my weight/height in kg/m)...I do my calc's in metric and convert to imperial to get a feel for the size and forces involved in a problem...hopefully I will eventually develop a better feel for metric and forget about imperial.
I am fairly young and I can't easily visualize metric (I need to do the math to give my weight/height in kg/m)...I do my calc's in metric and convert to imperial to get a feel for the size and forces involved in a problem...hopefully I will eventually develop a better feel for metric and forget about imperial.
MiketheEngineer,
I am in a new building here in Canada. The architects prepared their drawings in metric. The actual construction drawings were converted to inches and feet.
A lot of stuff is nominally sized in Imperial unts, but does not actually conform. Lumber and pipe comes to mind. You could just re-label these things in conforming metric units. For example, 1/2" [ ]pipe (Ø.840") can be called 14mm pipe.
JHG
I am in a new building here in Canada. The architects prepared their drawings in metric. The actual construction drawings were converted to inches and feet.
A lot of stuff is nominally sized in Imperial unts, but does not actually conform. Lumber and pipe comes to mind. You could just re-label these things in conforming metric units. For example, 1/2" [ ]pipe (Ø.840") can be called 14mm pipe.
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