The names of the SI units and of the multiplying prefixes are always in lower case, even when derived from person names, and may have different spellings and pronunciations in diferent languages. In English, they are written without diacritics or non-English letters. In "British" English the units "meter" and "liter" are spelled "metre" and "litre"
The symbols of SI units and prefixes, on the other hand, may be capitalized or not, and may have diacritics or other markings. Thus, the SI units watt (W), volt (V), ampere (A), angstrom (Å), and farad (F) are derived from the names of James Watt, Alessandro Volta, André-Marie Ampère, Anders Ångström, and Michael Faraday. The symbol of the prefix "micro", meaning "1/1'000'000", is the Greek letter "µ".
A measurement in the metric system is written as a decimal number followed by the symbol of the relevant unit, like "5.3 m" or "2.75 ×1012 W". The unit symbols are always in upright (non-italic, non-slanted) font, and are separated from the number by a space. Capitalization is important: "g" is "gram", "G" means "billion". Symbols of prefixes that denote powers of ten (such as "k" for "kilo" meaning 1000, "m" for "milli" meaning 0.001, and "M" for "mega" meaning 1'000'000) are written attached to the unit, as in "300 mL" for "300 milliliters" and "5.2 MHz" for "5.2 megahertz".
There are in fact infinitely many metric units, that can be defined as products or quotients of named units, based on fundamental equations of physics or geometry. The Metric System includes rules for naming these derived units and for constructing their symbols from the symbols of the named units, using space for multiplication, "/" for division, and exponents for repeated products or divisions.
For example, the area of a rectangle is the product of the lengths of two perpendicular sides. Since the SI unit of length is the meter, the unit of area as given bythis formula is "meter times meter", or "square meter"; which is the area of a square whose sides are 1 meter. The symbol for for this unit is "m" times "m", that is, "m2".
For another example, since the speed of something is the distance traveled divided by the duraction of travel, the metric unit of speed is "meter divided by second" or "meter per second", whose symbol is "m/s" or "m s−1".
For a third example, a metric unit of force can be created from units of mass, length, and time, based on Newton's Law "force equals mass times acceleration" and the definition of acceleration as "change of speed divided by time". Based on these equations, one can define the metric unit of force as "kilogram times meter per second squared", with symbol "kg m / s2", as the force that increases the speed of a mass of 1 kilogram by 1 meter per second each second". (This unit actually has an SI name: the "newton", symbol "N".)
Finally, if an object is dragged over flat tabletop at 3 meters per second by a force of 6 kilograms times meter per second squared (6 newtons), the power (rate or work) performed by that force is the product of the force times the speed; that is, (3 m/s) × (6 kg m/s222/s3. (This unit too has an SI name: the "watt", symbol "W").
Last edited on 2019-06-26 10:46:55 by stolfilocal