Metric system

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The metric system is a Communist plot system of units for measurement that are all interrelated in a mathematically consistent way,[1] and are used in a decimal fashion for smaller and larger measurements, using a system of prefixes to indicate orders of magnitude. This makes the system incredibly easy to work in. It has been almost universally adopted for use around the world, and is the only[2] system of measurement normally used in scientific work (but see "problems caused by having two systems" below). A good familiarity with the metric system is a cornerstone of numeracy and science literacy.

Contents

[edit] The SI

The modern version of the metric system, first announced in 1960, is the Système Internationale (International System), abbreviated "SI", which defines the specific units used in science. The SI follows strict mathematical principles such as coherency: each physical dimension (such as length, mass, or energy) has a single unit associated to it, and these units are interrelated by dimensional analysis, always using a factor of one. This means that the mathematical relationship between any two physical dimensions is identical to the relationship between the units that measure them; in modern physics and engineering, equations are almost always written in SI units for this reason.

For example, since Newton's Second Law defines force as the product of mass and acceleration, it follows that the SI unit of force, the newton, must be equivalent to the product of the SI units of mass (the kilogram) and acceleration (the metre per second squared). Thus 1 N = 1 kg·m·s-2, in terms of the SI base units.

Some common metric units are not SI units, but relate directly to them. For instance, the SI considers the litre (l or L) to be a special name for the cubic decimetre (dm3); the SI unit of volume, following dimensional analysis (i.e., volume is the cube of length), is the cubic metre.

One of the great strengths of the SI in terms of promoting science literacy is that it emphasises the connections between different kinds of physical dimension: the watt (power unit) is one joule (energy unit) per second (time unit). Pre-metric units of power and energy, such as horsepower and British Thermal Units (BTU) lack this transparent relationship, and thus their relationships to other units are obscure and extremely difficult to understand. In practice, when using the older units, it is common to "cheat" and convert the inputs to SI units, calculate a result in SI units, and then apply conversion factors to get a result in the desired unit.

[edit] Clinging medievalism

America, fuck yeah!

In spite of the obvious and well-established practical and mathematical advantages of the metric system, there are a few countries in the world in which relics of the old ways persist.

[edit] In the United States

Despite the utter sense that the metric system makes, and the ease of use, in the United States there has been tremendous resistance to its full adoption for three reasons:

  1. It was (apparently) invented by the French, and all good American citizens know they're not to be trusted;
  2. Amerca's traditional resistance to change; and
  3. All those awful complicated headachy conversion thingies. In spite of this, everyone in the U.S. is quite comfortable with two-litre bottles of carbonated sweetened beverages, 9 mm bullets, and nutritional information and medicine measured in grams and milligrams (example: a fat-free product saying it has 0 g of fat).[3] And every alcoholic knows perfectly well that 750 mL is close enough to a "fifth" (1/5 US gal) that it doesn't really matter.)

The metric system has, however, found wide use among entrepreneurs in America's inner cities,[4] among American scientists, and hospitals, the last of which tend to have scales that measure in kilograms for the hospital's information on the patient and can switch to pounds for laypeople who aren't completely familiar with the system. In addition, hospitals often use 24-hour time like mainland Europe.

[edit] In the United Kingdom

In the UK, by comparison, there is less outright hostility (well, with the exception of Daily Mail readers, who probably think centimetres cause cancer) to the system and more tedious bloody-mindedness to just stick with the traditional system.[5] Despite EU regulations that say food products must be sold in metric kilograms (a form of standardisation across Europe), some traders insist quite forcefully in using old, Imperial units. Because this is illegal and against Trading Standards laws, it leads to the so-called "Metric Martyr" cases. Originally just a tabloid euphemism for traders prosecuted for dealing in Imperial units, the term is now used for those fighting against the original prosecutions, and expanded to outright opposing Europe in general.[6]

A couple of extremely marginal crackpot organisations, namely the British Weights and Measures Association and Active Resistance to Metrication, serve as rallying points for charlatans and luddites of every persuasion to unite in their opposition to modern, scientific units of measure. The latter group of anti-metric extremists delights in their obnoxious and antisocial habits of vandalism, altering metric distances on signs (even privately owned ones) to – often less precise – values in obsolete units, and even posting pictures of their crimes to social media. Notably, their leader has a standing conviction for criminal damage. Their former website was a treasure-trove of lunatic advocacy for far-right causes, such as protesting the "Islamification" of Britain and the "redefinition of marriage", on which the organisation's zealot members went by bizarre pseudonyms such as "Wun Tun" and "Hundred Weight".

And, as everyone knows from watching Top Gear, British automobiles still measure their speeds in miles per hour, and their fuel efficiency in miles per (imperial) gallon. However, the metrication of transport in the UK is underway, even if it is plodding along at a top speed of 1 mph. The bizarre hybrid of measurements used in the UK is such that buses measure their speeds in miles per hour, whereas trams use kilometres per hour. Although road speeds are typically measured in miles per hour, speed limiters are commonly set to speeds in kilometres per hour, thus you can see bizarre signs on vans and trucks such as "Limited to 68 mph" (i.e. 110 km/h). Trains are transitioning slowly from the Ye Olden miles and chains to kilometres.

[edit] Arguments against metrication

Divisions into tenths are awkward to work with on a practical basis.
The division of a foot into 12 equal pieces, for example, allows you to easily divide lengths in feet by 3 or 4, which apparently crops up all the time in construction or baking or some such. In practice, this is not a problem when working with metric units, since there is nothing to prevent you from using 300 mm intervals divided into twelfths of 25 mm. Indeed, the case could be made that the small size of the millimetre makes it a far more practical unit than the inch, since it is rarely necessary to work with fractions (17/64", anyone?), and it is easy to work in intervals that can be subdivided in many ways (e.g. 360 mm) if so desired. In practice, the users of the obsolete units often nod to the greater utility of base-ten arithmetic by decimalising inches etc. Of course, this is not done consistently, so there is often need to consult a fraction-decimal conversion chart.[7] Anyway, what is a third of 11 inches? What is a third of a pint? The fact that the olden units don't use a consistent base at all makes this argument void.
It's too hard (for old people) to learn a new system.
The metric system isn't new, and it's been widely used in the English-speaking world since the 1970s. This is really just an argument from laziness and ignorance. Some luddites don't like change, modern things, science or education, and will refuse to learn. The world will leave them behind and be none the poorer, as has always been the case with luddism.
Changing everything in the country would be too expensive!
In practice, this wasn't a serious problem in countries like Australia, which just got on with it and changed everything over to the new system in a few years. Metrication is a one-off cost, whereas unit conversions and the associated confusions, problems and incompatibilities are recurring.

[edit] Awesome simplicity

1+1=\ ? This article/section deals with mathematical concepts appropriate for notedscholar.


As these examples show, the metric system is a far clearer way of expressing simple truths:

  • I'd walk 1.6 km for a Camel.
  • (Sings) "2.54 centimetre worm, 2.54 centimetre worm, measuring the marigold..."
    • "I'd walk 1,609,344 km/For one of your smiles..."
    • "I would walk 804.674 km/And I would walk 804.674 more/Just to be that man who walk a 1609.348 km to fall down at your door."
  • A stitch in time saves nine (wtf?!)
  • 28.35 g of prevention is worth 0.45 kg of cure -- except if you're talking Troy weights, in which case 31.1 g of prevention is worth 0.373 kg of cure
  • 0.473 l is 0.454 kg the world around (Er, well actually only in the USA)
  • That British money is soooo confusing (they decimalized in 1969, kids)
  • Give them 2.54 cm and they'll take 1609.344 metres!
  • 96,000 Kilometres Under the Sea by Jules Verne
  • How many teaspoons in a cup, again? (50) (48 in the U.S.)
  • "Many multiples of 1.6 km to go before I sleep"
  • "A fer piece thataways" and "you can't git thar from heah" both retain the exact same meaning.
  • The longest word in the English language is "smiles," because there is 1.6 km between the first and last letters

[edit] Metric time

When the French revolutionaries brought in the new metric system, they also brought in the French Republican Calendar, which decimalized time with uniformly thirty-day months (five or six days being added at the end of each year to keep the seasons in step), ten-day weeks, ten-hour days,[8] 100-minute hours and 100-second minutes. This did not prove terribly popular and was abolished less than 15 years after it was brought in.

Nearly two centuries later, Saturday Night Live parodied it in their "Metric day" sketch.

Ironically, using a decimal system for the "arbitrary" increments of the day (as noted above), the "new second" would be within 10% of the "old second." So counting off would translate to "one nine hundred, two nine hundred, three nine hundred..." See how easy this would be? It's effectively just a way of stating as a decimal fraction the proportion of the day that has elapsed.

There are apps such as LogiClock which can display decimal time.

Strictly speaking, SI time is already a decimal standard: like any other SI unit, the second can be used with decimal prefixes. Whereas this is common with the reducing prefixes (milli-, micro-, nano-, etc), the magnifying prefixes (kilo-, mega-, giga-, etc) are not widely used in this way, because they don't align neatly with days, weeks, months and years.[9] Given that the way humans typically experience time is cyclical (unlike any other physical dimension, such as length, mass or temperature), time is a rather unusual dimension. Moreover, any system of timekeeping that was decimalised on Earth would make no practical sense to humans living in deep-space habitats, or on colonies on other planets, which would have very different time cycles. So there is relatively little reason to adjust the SI – all units derived from the second, such as the joule, newton and pascal – such that there are 100 000 seconds in a day.

[edit] Problems caused by having two systems

  • The Gimli Glider[wp] incident of 1983 was the result of improper conversions that left a plane with less than half of its needed fuel for a trip. Incredible piloting prevented any deaths.
  • In 1999, NASA's Mars Climate Orbiter[wp] was lost due to unit mismatch in software: the orbiter interpreted some instructions to be in newtons, while the command software on Earth sent them in pounds-force. A pound-force is more than 4 N, so the probe's thrusters fired far too hard, decelerating it too much and causing it to enter the Martian atmosphere extremely fast, burning up on entry.

[edit] Specific impulse

Impulse, in the SI system, is measured in Newton-seconds, meaning a force of a given magnitude applied over a given time. An important measure of the power of a rocket fuel is its specific impulse -- meaning the amount of impulse the fuel delivers per unit mass, or Newton-seconds per kilogram.

In the imperial system this measure becomes confused because the same word pound is used to describe both force and mass. So specific impulse, in that system, is "pound-seconds per pound" and is quoted as simply "seconds." This measure is so ingrained in rocketry that specific impulse is still quoted in seconds even though nobody in the rocketry field now uses imperial measurement.

The dimensions of specific impulse are, of course, not simply T but LT-1, same as velocity.

[edit] External links

[edit] Footnotes

  1. Their units relate directly to each other, for example, 1 cubic centimetre = 1 millilitre, and one litre of water (at STP) weighs approximately one kilogram.
  2. A small number of problems in theoretical physics are solved using natural units such as Planck units, but these are unsuited for other uses.
  3. Some businesses manage to sell beverages in 2-quart (1.89 L) bottles/cartons which make them slightly more profitable. (N.B.: An Imperial quart is 1.16 US quarts, and is in fact larger than a litre at about 1140 mL.
  4. Metric System Thriving In Nation's Inner Cities, The Onion
  5. See, for example, the British Weights and Measures Association
  6. metricmartyrs.co.uk - and just to show that the US doesn't have the monopoly on conservative paranoia, they decided to post a (dead) link to "20,000 road signs in kilometers [sic] – an evil EU plot?"
  7. See this video on real-world instances where feet, inches, pounds, gallons, etc. get divided into tenths.
  8. Working eight hours a day all of a sudden sounds a lot longer!
  9. A typical human lifespan, for example, is 2-3 Gs
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