Metric or Imperial??

[clarinetJWD]

I don't really like Celcius, though...maybe we should all switch to Kelvin.

 

[Benthic]

<snip>
Also: We (the US) need to just go cold turkey and scrap the imperial system. THere would be measurement confusion for a few years, but eventually we'd be able to communicate to the rest of the world without converters...

Amen to that! I think the US Gov't should drag the country (kicking and screaming if necessary) to the metric system. I grew up on the Imperial system, but I see many advantages to the metric system.

My wife, on the other hand, hates the metric system. Her argument usually something like, " I know how long a yard is, but I don't know how long a meter is." I've tried to remind her that she would learn and that once upon a time she didn't know how long a yard was, but she learned that just fine. No luck though.

Brian

 

[Jeff Canes]

The US officially when to metric in 1975 but in the late 80&#8217;s it was changed from the official to preferred system

 

[BoblyBill]

I don't really like Celcius, though...maybe we should all switch to Kelvin.

LOL... Man, it was like 263 K today. I had to go get a jacket...

 

[BoblyBill]

pounds mass and pounds force are the same on earth... on the moon they are different.

 

[Helen B]

The pound (symbol lb) is a unit of mass (dimension M).

The pound force (symbol lbf, the f may be written as a subscript) is a unit of force (dimension MLT-2), being the force due to Earth's gravity acting on a one-pound mass.

Screwed up units: air conditioners with electrical power stated in kW, compressor motor power stated in hp (or is it HP?) and cooling power stated in BTU/hr when all powers could be stated in kW.

Oh, and then there's the use of capitals for SI unit names. In SI it is kelvin, watt and volt not Kelvin, Watt and Volt. The symbols (they are symbols, not abbreviations) may be capitals if they are named after someone (eg K, W and V) but the unit names are not capitalized, unless they would be by the normal rules of grammar, such as at the beginning of a sentence.

Best,
Helen

 

[Mitica100]

^^
Helen, you always continue to amaze me!!! :thumbup:

I grew up in a metric system, had to spend a few years to get used to the Imperial system. I still have troubles once in a while but what's sad now is that I have more troubles in metric!

 

[BoblyBill]

There is a little problem with pound-mass. Take this for example.

You can find this all over the net, but the convertion between pounds mass and kilogram is 1 lbm = .45359237 kilograms or just 1 lbm = .45 kg. Now we can find that force in Newtons, we get .45*9.806=4.4127 N. We then can convert this to pounds-force and that convertion is .224 lbf/N*4.4127 = 1 lbf. Now that we had this in force we should be able to divide by 32.2 ft/s^2 to get mass but now we are left with a mass that 32.2 (.0310559) times smaller than what we started out with. Basically, when you are converting between metric and SI, you would be able to go from mass (SI) to force (SI), force (SI) to force (metric), force (metric) to mass (metric), mass (metric) to mass (SI) and still come up with the same number you started out with. But with this, you can't...
If you take this chart and go clockwise or counter clockwise you should always end up with the same numbers, but with pounds force and pounds mass used you get bigger and bigger numbers if you go clockwise and smaller and smaller numbers going counter clockwise, but is you use slugs and pounds-force then this you will always end up with the same numbers that you start with.

Force (SI) Force (metric)
Mass (SI) Mass (metric)


Pounds-force and pounds-mass are equal, and to get rid of the confusion get rid of pounds-mass and just have pounds for force and slugs for mass. The actual definition of a pound-mass is: the amount of mass that “weighs one pound or pound-force.” Were as the definition of the slug is: the amount of mass that a one pound force will accelerate to one foot per second squared. These are completely different.

 

[Helen B]

There is a little problem with pound-mass. Take this for example.

You can find this all over the net, but the convertion between pounds mass and kilogram is 1 lbm = .45359237 kilograms or just 1 lbm = .45 kg. Now we can find that force in Newtons, we get .45*9.806=4.4127 N. We then can convert this to pounds-force and that convertion is .224 lbf/N*4.4127 = 1 lbf. Now that we had this in force we should be able to divide by 32.2 ft/s^2 to get mass but now we are left with a mass that 32.2 (.0310559) times smaller than what we started out with. Basically, when you are converting between metric and SI, you would be able to go from mass (SI) to force (SI), force (SI) to force (metric), force (metric) to mass (metric), mass (metric) to mass (SI) and still come up with the same number you started out with. But with this, you can't...

I hadn't seen that before but it is quite funny, and it shows how an inconsistent set of units can lead to gross misunderstanding.

The conversion from lbm to lbf is

lbf = lbm x ft/s2 / 32.2

As often happens, inconsistent units require constants where a consistent set does not.

Slugs, lbf and ft/s2 are a consistent set:

lbf = slugs x ft/s2

Kilograms, newtons and m/s2 are a consistent set:

N = kg x m/s2

Now, put the formula

lbf = lbm x ft/s2 / 32.2

into the little 'problem' and no matter how you calculate it, it always works out correctly.

Best,
Helen

 

[dklod]

Purely metric here.
Can't make head nor tail out of baby measurements when the babies were born in Britain, the States or Australia. Neither weight nor length. All I can ask back is "Would that be considered 'normal'?" When the answer is "Yes, pretty average", I get the idea.
I have more of an idea of what temps in Fahrenheit are as compared to our Celsius-grades. But once we enter the field of cubic measurements, I'm totally lost when someone gives me an imperial measurement.

On the baby thing, we still measure babies in pounds at times. But its seems everywhere to get that baby out, the mum to be needs to be 10cm dialated, not 4 inches.

 

[mrodgers]

On the baby thing, we still measure babies in pounds at times. But its seems everywhere to get that baby out, the mum to be needs to be 10cm dialated, not 4 inches.

Good one, it's the same here. I forgot about that one.

 

[usayit]

Most college level sciences and engineering in the United States is taught in metric. Architecture is still taught in Imperial. How is Architecture taught in other countries outside of the U.S? Just curious....

 

[BoblyBill]

I hadn't seen that before but it is quite funny, and it shows how an inconsistent set of units can lead to gross misunderstanding.

The conversion from lbm to lbf is

lbf = lbm x ft/s2 / 32.2

As often happens, inconsistent units require constants where a consistent set does not.

Slugs, lbf and ft/s2 are a consistent set:

lbf = slugs x ft/s2

Kilograms, newtons and m/s2 are a consistent set:

N = kg x m/s2

Now, put the formula

lbf = lbm x ft/s2 / 32.2

into the little 'problem' and no matter how you calculate it, it always works out correctly.

Best,
Helen

Which means that on earth like I said a couple of posts above lbf and lbm are the same value:

lbf=lbm*32.2. ft/s^2/32.2...

Different units but they have the same value...

 

[Helen B]

Which means that on earth like I said a couple of posts above lbf and lbm are the same value:

lbf=lbm*32.2. ft/s^2/32.2...

Different units but they have the same value...

I wasn't disputing that, merely pointing out the major error in the 'little problem' you quoted: there is no problem if the correct relationship is used, which it wasn't in the 'little problem'.

Best,
Helen

PS In the USA, the pound is legally defined in terms of the kilogram, not by its relationship with the pound force.

 

[slapshot™]

How is Architecture taught in other countries outside of the U.S? Just curious....

In Canada, for the most part, Engineering firms use metric. Civil works (road building) are exclusively metric. Practically most buildings are designed using metric, however you do on occasion find a renagade outfit that insists in using English (or, Imperial) measurements.

In road construction (to which I am employed) we tend to switch back and forth as we are bilingual. Aggregates will be discussed either in yards (yd3) or cubes (m3). We measure our materials in mass as tonnes but never really discuss them in pounds or tons. Lineal measurements in inches/feet or millimetres/metres/centimetres. Usually smaller measurements would be easily translated in inches or millimetres (4" = 100mm) or (5' = 1.5m), but longer measurements tend to revert back to metres - usually anything over 20' (6.1m).

I guess I'm from an age where I'm lucky. When Canada made the switch I was in my teens and young enough to adapt. However, when it comes to larger areas and talking hectares to me you might as well be speaking Greek. Western Canada was surveyed using miles (township and range system) and acres. I can grasp the concept of 640 acres - 259 hectares, not so much.