What are the advantages of using international systems of Units (51)
Answers
Answer:
1. has only one unit for each quantity.
Answer:
Advantages of SI System of Units
It is a coherent system of units.
It is a rational system of units.
SI is a metric system.
The three systems of measurement in common use — USCS (USA), Imperial (UK & Commonwealth), and Metric/SI (everyone) — were each developed, within a few decades of each other, as solutions for the morass of units that came before.
All three share these advantages:
Consistency - Unlike previous units, each of these are now entirely consistent. (A pound is always the same weight or mass, for all commodities, for all times, an in all places.)
Systems - Unlike previous units, these the units of these all inter-relate. Force equals mass times acceleration in a consistent set of units, etc.
Familiarity - In each country where they are in use, or each profession, the units are familiar and comfortable. Common standards exist for every type of product. Tools and measuring devices exist. The systems are learnable, workable, usable, and familiar. Unit conversions are understood, in the places where each system is common.
All three share disadvantages:
Time is not decimal. Even SI picked the arbitrary “second” over the natural “day”.
Problems distinguishing weight and mass. SI has separate units for them, and USCS & Imperial use the same unit for them, but all have problems. (No one weighs themselves on a bathroom scale calibrated in Newtons.)
Frankly, ~95% of people have difficulty understanding why we distinguish them at all. “Mass” was first distinguished with SI. Non-SI did not have “pounds-force” and “pounds-mass” until SI came along and screwed up the identity between weight and mass.
And between the systems, we typically convert between weight pounds and mass kilograms, which is kind of crazy.
And ALMOST NO ONE in USCS/Imperial uses slugs for mass. (I have. But I lived to tell the tale.)
Non-SI units (USCS and Imperial) have these additional advantages:
There is a unit available for every common size need.
(Having SI units spaced out by factors of 1000 is not very convenient.)
(Note: In some places, in some applications, closer units are used - decilitres, centimetres, etc. But deka- and deci- are uncommon in most applications.)
Those multitudinous units are very human units. They intimately relate to the things people do with units.
(It’s not the same thing to quaff a half-litre instead of a pint. Or to buy bread in a 0.5 kg loaf instead of a pound. Or take 5 ml of cough syrup instead of a teaspoon.)
No silly base units.
A gram is so insignificant that SI uses a kilogram as the base unit. Totally violates the spirit of the system.
A Joule may well be 1 kg-m^2/s^2 (nice formulaic conversion), but it’s pretty useless as a unit. Megajoules are much more common. And calories! 1 (lg) cal = 4600 J. Why do different scientific disciplines differ on whether they view reactions in Kcal or MJ ? Ugh.
Non-Si tends to have extra units, while SI tries hard to reduce everything to the basic 7 by expressing these quantities as multiplications or divisions of the basic 7 units. (The “metric system” has extra units too — but not the SI, which tries to be pure.)
Square units. Though the French tried to define the “are” as a unit of area (10m square), it didn’t stick. Non-SI has square inches, square feet, square yards, acres, and square miles. In SI, there is *NO* unit convenient for area like the acre. The metric system tries to extend SI with extra units, with limited success. There is the hectare - which is 100 times (hecto-) a 10 m square (are), but it is not actually part of SI, nor is it like all the other units (e.g., 10 Kilo-square-metres, or 0.01 square kilometre = 1 centi-square-kilometre = 0.01 mega - m^2))
There are often unit conversions that include a factor of 3, and this allows easy division of things into 3’s, 6’s, 12’s, etc. This does not occur in SI, which has multiples of 10 = 2 * 5.
Candlepower. Foot-candles. Pretty straight forward. Very human. As opposed to the SI distinctions between lumens, candelas, and lux, let alone between ANSI lumens and other lumens.
Non-Si units (USCS and Imperial) have these additional disadvantages:
For any given dimension (e.g. length), there are different conversion factors between the various units. (12 inches in a foot, 3 feet in a yard, 1760 yards in a mile) (SI’s 10, 100, or 1000 between units requires no remembering.)
When crossing multiple unit sizes, non-SI requires a series of multiplications, instead of SI’s moving the decimal point. (How many teaspoons in a pint? 3 x 2 x 8 x 2.) The classic “furlongs per fortnight”.
This is the most common complaint from SI users. Inches to miles, or square inches to acres.
NOTE: If you use the metric systems extra units instead of the pure SI units, then you have the same problem! How many cm^2 in one hectare?