Metric VS English engineering system of measurement

[timthereaper]

My brother in law used to be a science teacher at the middle school level in Mexico. Once I asked him when talking about how much less a person would weigh on the moon, did he use kilograms or Newtons. He used kilograms. He didn't even know what a Newton was.

Imperial units aren't much different with pound mass vs pound force, but it's good to see that that us Amurricans aren't the only ones that are screwing our kids up for the future.

 

[skeptic2]

Too many damn units in metric anyway. You need a dictionary to navigate through them all.

Too many units in metric! Check this out.

http://en.wikipedia.org/wiki/English_units

 

[gmax137]

So we can compete in the global market. Globalization is going to eventually make the US "go metric", with or without a government mandate. The US is no longer the economic powerhouse it was in the post WWII days. You can see this happening now. Some of the goods you buy have a goofy size in customary units, a nice clean size in metric units. Manufacturers that want to compete in the global market have no choice but to package goods in nice multiples of metric units. It's a whole lot cheaper if they sell those same size goods to the US market, with only a change in the label...

This is probably true - the manufacturer's will do whatever maximizes their profits. Though it is simpler for some (say soft drink companies) than others (umm, people making pipe fittings for NPS size pipes). There is more to international sales than package sizing. Keeping with the soft drink guys, have you tasted Mexican Coke? Still made with real cane sugar and it does taste different.

As far as school / jobs / doing calculations: if you can do a calc in one set of units but not another, chances are you don't really understand what you're doing (IMO). Some types of calcs are simpler in one set of units or another, but the physics you're modeling doesn't care about the units you use.

 

[PhanthomJay]

As far as school / jobs / doing calculations: if you can do a calc in one set of units but not another, chances are you don't really understand what you're doing (IMO). Some types of calcs are simpler in one set of units or another, but the physics you're modeling doesn't care about the units you use.

True, but if you are used to one system, you don't have a 'feel' for the other, as has been pointed out several times in this thread. If i were to size a structural beam in metric units of length and weight (or is it mass), using an allowable stress of so many millions of Pascals, I would be lost as to whether my calcs made sense. Could probably be off by a factor of 1000, and I wouldn't initially know. Very bad for productivity. And the steel mills.

I wonder what a 2 X 4 piece of lumber, which measures not quite 2 inches by 4 inches, is called in other countries? Please advise. I know what a 2 X 4 is, but not its metric counterpart name.

 

[Travis_King]

http://www.diy.com/diy/jsp/bq/nav.jsp?fh_location=//catalog01/en_GB/categories<{9372016}/categories<{9372053}/categories<{9372280}/categories<{9392123}&fh_reftheme=promo_159030093,seeall,//catalog01/en_GB/categories<{9372016}/categories<{9372053}/categories<{9372280}&fh_refview=summary&icamp=ns_2&ecamp=Aff-85386&awc=483_1379451378_7a694c05c55334b2bff0b9e406860136&noCookies=false

 

[SteamKing]

Too many units in metric! Check this out.

http://en.wikipedia.org/wiki/English_units

Most of these units are archaic and no longer used. In Engineering calculations, the foot, the inch, the pound (and its big brother, kip), degrees F or R, maybe the gallon, and the long and short ton are about all the units one will encounter. Statute miles and nautical miles are used for measuring large distances.

For non-engineering work, you'll come across an occasional furlong (horse racing). A parcel of land will have its area expressed in acres. Grain will have wholesale prices quoted for a bushel.

The point is, USCS works more often with basic units than SI does. USCS doesn't use a lot of derived units with funny names.

 

[D H]

The point is, USCS works more often with basic units than SI does. USCS doesn't use a lot of derived units with funny names.

Are you serious? BTUs? Horsepower? Candlepower? And of course,

 

[gmax137]

Pat, working in New York, carries a 50 pound sack of mortar mix up a 20 foot flight of stairs. How much work did Pat do on the sack?

20 * 50 = 1000 foot-pounds

What's so hard ?

 

[Baluncore]

Imagine; you are flying over Britain, on a moonless night in 1940, at a speed specified in knots, (nautical miles per hour), at a height measured in thousands of feet, on a magnetic compass bearing in degrees, (angle, not Fahrenheit or Celsius), on a chart referenced to Grid North. Your latest AI, (Air Intercept set), is on the blink, and the cabin heater has iced up. You must somehow find your way back to base.

The AA, (Anti-Aircraft), artillery will now take over. The artillery uses maps printed at a scale of inches per mile, but divided into 1000 metre squares. It uses ground range measured in yards, but height in feet. Elevation is measured in degrees, but azimuth is corrected, not in degrees, but in “mils”, (an offset of one in a thousand, (no, not thousandths of an inch, nor millimetres)).

Your enemies fuel gauges are calibrated in litres, your fuel gauges are calibrated in gallons(imp), (4.546 litre). In a couple of years time, (if you survive), when you begin flying a US built aircraft, the gauges will be calibrated either in pounds of fuel, or in gallons(US), (3.79 litre), but refilled from bowsers still calibrated in gall(imp). As allies you will soon be united in a cold war. United politically that is, but still separated by your inconsistent units of mensuration.

For short term survival it is essential that you use what you now have available, but in the longer generational time-scale it is wise to convert to one consistent set of units across science, engineering and commerce. Should that conversion be a progressive evolutionary change or a unit step ?

The USA does not yet use the fundamental ISO metric unit of length, the “metre”. It uses the “meter”. We will know that the USA has finally “gone metric” when their spelling of that unit changes to conform to the ISO definition.

 

[Baluncore]

Grain will have wholesale prices quoted for a bushel.

Which bushel would that be ? Is it a weight or a volume ?

 

[D H]

Pat, working in New York, carries a 50 pound sack of mortar mix up a 20 foot flight of stairs. How much work did Pat do on the sack?

20 * 50 = 1000 foot-pounds

What's so hard ?

Which foot? The survey foot or international foot?

Also, express your answer in horsepower-hours, please.

Assuming Pat works at 30% efficiency, how much energy did he use? Express your answer in BTUs. Mean BTUs, International Table BTUs, and 59 °F BTUs. Different engineers use different BTUs.

Assume the work is done by a pump. How much work is done? (Hint: Hydraulics engineers use a different horsepower than mechanical engineers.)

How much water flows through the pump? Express your answer in fluid ounces, gallons, barrels, cubic feet, cubic yards, and acre feet.

 

[SteamKing]

Which bushel would that be ? Is it a weight or a volume ?

I really couldn't say, since a bushel is not used much in engineering. A commodities merchant would know.

 

[D H]

The USA ... uses the “meter”. We will know that the USA has finally “gone metric” [strike]when their spelling of that unit changes to conform to the ISO definition.[/strike] when ISO 80000 is modified to allow US spelling of the meter and liter.

There you go. Fixed that for you.

The US will never spell the meter as "metre". Never.

 

[D H]

I really couldn't say, since a bushel is not used much in engineering. A commodities merchant would know.

Are you saying that agricultural engineers aren't engineers?

 

[SteamKing]

"(Hint: Hydraulics engineers use a different horsepower than mechanical engineers.)"

http://en.wikipedia.org/wiki/Horsepower

1 HP = 550 ft-lbs/sec, even for hydraulic engineers = 2544 BTU/hr

1 BTU = 778 ft-lbs of energy

Bushels are dry measures that are units of volume. 1 US bushel = 2150.42 cu. in.

As to the foot, the 12-inch foot is just fine. International feet v. survey feet:
http://microstationtoday.com/microstation-tip-corner-survey-foot-versus-international-foot-whats-the-difference/

 

[Baluncore]

Millers' statements as to the number of sacks, bushels or coombs of corn they have ground are often confusing, and the following may help to light up their remarks. One 'sack' equals four bushels or one coomb, and two coombs equal one 'quarter'; but the avoirdupois weight of a bushel is not constant, thus a bushel of wheat is 63 lb., barley 56 lb., oats 42 lb. and beans 77 lb; so a coomb of wheat is 252 lb. or 18 stone, barley 224 lb. (16 stone), oats 168 lb. (12 stone) and beans 308 lb. (22 stone), and a quarter of wheat is 4½ cwt., barley 4 cwt., oats 3 cwt. and beans 5½ cwt. A 'quarter', avoirdupois, is a quarter of a hundredweight - 28 lb. Beans are 4¾ cwt - 532 lb. - in modem milling. The sack of grain is called a 4-bushel sack'; the term '20-stone sack' (2½ cwt.) is applied to a sack of flour; the coomb is a measure of grain, not of flour.

 

[Baluncore]

There you go. Fixed that for you.

The US will never spell the meter as "metre". Never.

Nevre evre ?

 

[skeptic2]

Pat, working in New York, carries a 50 pound sack of mortar mix up a 20 foot flight of stairs. How much work did Pat do on the sack?

20 * 50 = 1000 foot-pounds

What's so hard ?

I have worked with a number of motor and motor drive manufacturers who consistently refer to the torque of their motors in foot-pounds instead of pound-feet.

 

[gmax137]

I have worked with a number of motor and motor drive manufacturers who consistently refer to the torque of their motors in foot-pounds instead of pound-feet.

Personally, I never really bought into this ft-lb vs lb-ft thing. Seems to me Torque and Work have the same dimensions

[M][L]²[T]^-2

no matter what units system you're following. Does anyone think "meter-Newton" is work and "Newton-meter" is torque? Or should that be "Newton-metre"

 

[PhanthomJay]

Ft-lb is the accepted unit for both torque and work. I have never seen either referred to as lb-ft in the US.

 

[SteamKing]

Torque outputs in the car magazines used to be quoted in units of 'lb-ft' and they still are.

http://www.motortrend.com/roadtests/convertibles/1307_2014_chevrolet_corvette_stingray_z51_first_test/

 

[Baluncore]

I have never thought of “foot.pounds” or “pound.feet” as distinct units.
I still believe that multiplication is commutative.

 

[D H]

Some apparently like to use different names for the units for torque and energy. This distinction with pound-feet for torque, foot-pounds for energy, goes back to 1900. Others don't care. They use foot-pounds for both.

Aside: That distinction seems bass ackwards to me. Torque is $\vec r \times \vec F$, so the units should be feet*pounds to indicate how torque is calculated. Work is $\int \vec F \cdot d\vec l$, so here the units should be pounds*feet. But the convention is the other way around.

 

[WaaWaa Waa]

As was already mentioned in the thread, the metric system is used in the US. So is the old imperial system. You are free to use whatever you like in the US, that's what freedom is all about. ;) Freedom necessarily includes the freedom to make bad decisions, like imperial units. I don't use them though. I use the metric system personally and have yet to have storm troopers knocking at my door.

I recently followed The American Society Of Civil Engineers page in Facebook. I found that they are using only Imperial Units. Now, don't get me wrong. I have nothing against the Imperial Unit whatsoever On the contrary, as a civil engineer myself I applaud the American civil engineers for their achievements using the Imperial Units

 

[SteamKing]

There are a lot of legacy structures which were designed and built using imperial units in the US and in the Commonwealth. There is still a lot of holdover in state regulations and reporting standards regarding public works projects. You have to report the amount of Earth moved in an excavation, for example, in cubic yards instead of cubic meters. Construction materials are manufactured and sold using imperial measures rather than metric.

 

[2milehi]

Torque outputs in the car magazines used to be quoted in units of 'lb-ft' and they still are.

http://www.motortrend.com/roadtests/convertibles/1307_2014_chevrolet_corvette_stingray_z51_first_test/

I wouldn't put too much weight in that presumptuous snob magazine where the readers of that rag never have performed an oil change in their life. Any real gear-head magazine will state ft-lb of torque.

 

[2milehi]

I recently followed The American Society Of Civil Engineers page in Facebook. I found that they are using only Imperial Units. Now, don't get me wrong. I have nothing against the Imperial Unit whatsoever On the contrary, as a civil engineer myself I applaud the American civil engineers for their achievements using the Imperial Units

The surveying tapes are in 1/100 of a foot.

 

[SteamKing]

Land surveying is one of those professions in the US where the law prescribes certain things. Land descriptions are regulated by the various state governments, and the surveyor obviously must comply with those regulations in doing survey work. The US has been surveyed using the imperial system, and the various state plane coordinate systems have also been laid out using imperial units.

When expansion started westward in the late 18th century, the land was divided into square townships which measured 6 statute miles to the side. There were further subdivision in each township, and if you read the legal description of a parcel of land, it will make reference to the township and subdivision within the township in locating that parcel.

 

[xxChrisxx]

To be fair lengths are easy enough to just convert as a design exercise. It's a bit more of a pain to have to own two sets of spanners and sockets.

The true pain in the arse is designing a piece to mate two threaded components together. One with a metric thread, the other with a UTS. Doubly so if they are very similar in pitch, but they still need different gauges.

 

[SteamKing]

That's a big reason why metric conversion in manufacturing took so long. Fastener standards took a long time to standardize across industry, and manufacturers in the US were very reluctant to start the process over with metric fasteners. In the UK, with the Whitworth system, special tools were required which could not be used on US fasteners. Since modern machinery is very dependent on standardized fasteners, this is no small consideration in whether to go metric in your manufacturing sector.

http://en.wikipedia.org/wiki/Screw_thread#History_of_standardization