Meters, liters, kilograms, and degrees Celsius come more easily than others based on many years in the lab working with those units. I can't recall the last time I thought about any Newtons except those with the fruit filling. Just not a unit I commonly come across. The IEEE published a good unit-conversion book, "Metric Units and Conversion Charts," by Theodore Wildi that helps simplify moving between measurement units.
For some reason, I don't need to make a conversion in my head when I'm talking about liters, meters or kilograms. Newtons, however, is another matter. When someone expresses Newtons to me, I absolutely have to sit down and convert it to pounds-force. I just don't have an intuitive reaction when someone says, "This is 50 Newtons."
Robertson-head screws and tools prove difficult to find here in the US. I have a set of screwdriver bits and use them mainly for screws in electrical panels. I suppose those panels and circuit breakers have customers in Canada and the US. For an interesting and related book, see:
"One Good Turn: A Natural History of the Screwdriver and the Screw." Amazon has it in paperback for about $US 6. --Jon
p.s. It would help if this darn blog-post tool provided more control over fonts. Sorry about the big bold characters.
Ahhh.. the Robertson!. It was the greed and stubborness of Henry Ford that prevented an intelligent long-term deal with Robertson (Ford was already saving a lot by using those screws, but he wanted more). Robertson fasteners have a lot of qualities, but few people have used them. Can be torqued tremendously without rounding either the hex head or the "Allen" wrench; you can hold them very securely on the end of the Screwdriver w/o letting them fall inside the engine bay or worse, they are a joy to use single handedly. It is not only a pitty, but a shame that this truly excellent design was NOT used in cars. Car maintenance and Hot rodding would be much easier with them! I'm happy using them for high quality speaker cabinet construction and to build electronic chassises where a single slip of an screw driver would mean an ugly scratch on the front panel; and the joy of using them completely justifies their price.
@William K: I've seen torque given in inch-ounce, inch-pound, and foot-pound units. For some reason, I've never seen foot-ounce units, but I don't doubt that they exist. This causes no end of confusion.
I've also heard that the correct terminology for torque is actually ounce-inches, pounds-inches, and pounds-feet. This is supposedly in order to distinguish energy in foot-pounds (a scalar quantity) from torque in pounds-feet (a vector quantity). Of course, nearly no one uses this "correct" terminology.
At any rate, the "correct" terminology seems kind of silly, since multiplication is commutative, and there is no difference between multiplying 1 lb by 1 ft and multiplying 1 ft by 1 lb; it only matters whether you take the scalar (dot) product or the vector (cross) product.
In SI, torque is in newton-meters, and energy is in joules (1 J = 1 N · 1 m). This is at least more credible than the idea that, by changing the order of the words, you can distinuish a dot product from a cross product.
By the way, although I seem to be defending the metric system, I'm personally much more comfortable with inch units, and prefer to use them wherever possible. This is just a matter of custom and familiarity, more than anything else.
Pilots have to deal with mixed measurement systems as a matter of course, but at least the systems don't need to relate to each other. Speed and distance are in knots, altitude is in feet, temperature is in Celcius, you get the idea.
I never ever use units of ounces or feet. Mixed units of measure are an invitation to errors, and should be avoided for that reason, if for no other. Certainly those conversions are quite inconvenient, which is always quoted by those touting the metric system, but simply avoiding mixed units is very simple and very effective, and should have been done 50 years ago.
@William K: Multiplying a pressure in kPa by an area in cm² gives you a force in units of 0.1 N (1000 · .01²), so you just have to move the decimal point one place to the left. That's a lot easier than dealing with conversion factors of 12 (inches/foot), 16 (ounces/pound), etc. And multiplying pressure in MPa by area in mm² gives force in N directly.
ab3a, I understand where you are coming from, but I cannot agree with you. The units like nautical miles are really not used by most of us. Even if the polot is using them, the passengers see statute miles on their display for example. Actually, the foot and yard are fairly arbitrary as well as the meter. Should we go back to the cubit?
When I was living in England a few years ago, there was a scandal becuase food vendors were being forced to switch to metric. The argument used was the one you use, about being able to easily split things in half, then in half, etc. That is fine when there is no technology, but these same vendors had electronic payment decvices in their shops.
I always found it easier to calculate complicated things in my head (such as area and volume) with the metric system. Frankly, it is the same reason we picked a decimal currency system.
Long before the French developed the Metric system, the British had theirs. They built a huge level of commerce around it. The US continued with that system, slightly modified and it still remains to this day.
Much of the US system was worked up around carefully developed rules of thumb. The metric system was not. It was developed from arbitrary fundamental scientific units that had little relation to much of anything. Take the original definition of the Meter: It was based upon a ten millionth of the meridian from the pole to the equator through Paris.
That's not a particularly useful number. The Nautical Mile was based upon the Mercator Projection and it was intended to be about 1 minute of arc along any meridian. To this day, pilots and mariners still use this approximation.
From a practical perspective, the standard units were intended to be commonly used. The Metric system, well it fell wherever it fell.
The Metric system is based upon the notion that everyone has ten fingers. But a much more realistic system would go binary. 1/2, 1/4, 1/8, 1/16, 1/32...
This gets you exactly the precision you measured, not some ideal number plus or minus some slop.
The reason why the standard system is still here is because it was meant to be used without a calculator. Nobody thinks much about how it came about and how arbitrary the metric system really is.
We still use degrees. Does anyone use Grads? We still use millibars, does anyone use kPa for the weather?
The metric system was not meant to be used by mortals. It gives the illusion of precision whil the units are actually impractical as can be.
But I guess in this day and age, where mental computation seem as outmoded as a slide rule, Where measurements are made automatically by machine, those older systems "don't make sense." Go figure...
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