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Basic Metric & Measurements

Metric Notation

With English units we add a suffix to denote very large or very small quantities. For example, "seven million" In the metric system a prefix is added to the unit, as in "seven megabucks" which would be seven million dollars. Similarly a kilobuck would be $1000, a decibuck would be a dime and a centibuck would be one cent. Below is a list of some of the prefixes used by the metric system preceded by their abreviation. Also included for completeness are the numbers shown in Scientific Notation and their English name.

  
       Metric       Standard        Scientific   United
      Notation      Notation         Notation    States   

     (T)   tera   1000000000000        1012     trillion 
     (G)   giga   1000000000           109      billion 
     (M)   mega   1000000              106      million  
     (k)   kilo   1000                 103      thousand 
     (h)   hecto  100                  102      hundred  
    (dk)   deca    10                  10       ten  
     (d)   deci     0.1                10-1     tenth  
     (c)   centi    0.01               10-2     hundredth  
     (m)   milli    0.001              10-3     thousandth  
     ()   micro    0.000001           10-6     millionth  
     (n)   nano     0.000000001        10-9     billionth   
     (p)   pico     0.000000000001     10-12    trillionth  

Note that "" is the Greek letter mu. Only in the United States Medicine is 'g' replaced by 'mcg'. [both microgram]

Please DO NOT confuse "m" and "M". Aspirin is measured in mg (milligram) and a Mg (megagram) is called a metric tonne. A mm is less than .04 inches but a Mm is more than 621.37 miles, about the distance from San Diego to Salt Lake City.

Fundamental Metric Units

The unit of length is the meter (m).
The unit of mass is the kilogram (kg).
The unit of time is the second (s).
The unit of current is the ampere (A).

The meter (m) is the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second. [i.e. by definition, light travels 29.9792458 cm in a ns.]

The kilogram (kg) is the unit of mass; it is equal to the mass of the international prototype of the kilogram. [Essentially the mass of a liter of water at 4C.]

The second (s) is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom. [Duration chosen to equal what was a mean solar day divided by 86400.]

The ampere (A) is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 x 10-7 newton per meter of length.

Derived Metric Units

One liter (l), a measure of volume, is a cubic decimeter.

A metric tonne is 1 Mg. [1000 Kg]

One newton (N) is the force needed to accelerate 1 kg at 1 m/sec2. [In San Diego gravity attracts 1 kg with a force of about 9.8 newtons. The weight of 1 kg varies between the equator and the poles. It also varies with time of day. Standard gravity is defined as 9.80665 m/sec2. ]

One pascal [Pa] is a pressure of 1 N/M2. Standard Pressure [one atmosphere] is about 101.325 KPa.

Air density at sea level and 20C is about .001205 g / ml. [water at 4C is about 1 g / ml]

One joule (J), a measure of energy, is 1 newton-meter of work. It is also equal to 1 watt-second of energy. A kilowatt-hr is 3.6 MJ [megajoules]. To raise a liter of water [on Earth] one meter requires about 9.8 joules of work.

One watt (W), a measure of power, is one joule per second or one newton-meter per second. The power needed to raise a liter of water [on Earth] one meter in one second is about 9.8 watts. One ampere through an electrical resistance of one ohm develops an EMF of one volt and dissipates one watt of power. Power is the rate that energy is used.

One ohm (S) is the electrical resistance of a uniform column of mercury at 0C, 106.4 cm in length with a mass of 14.4521 g. A current of 1 ampere though a resistance of 1 ohm disapates a power of 1 watt.

One volt (V) is the electrical potential across a 1 ohm resistance through which flows a current of 1 ampere.

The degree Celsius (C) [aka centigrade] is the same difference as the degree Kelvin, but zero on the Celsius scale is at the freezing point of water and 100 on the Celsius scale is the boiling point of water at 1 atm.

One hertz (Hz), a measure of frequency, is the number of times something happens per second. It replaces the old unit 'Cycles per Second' (CPS). The frequency of a periodic function is the reciprocal of the period in seconds.

Derived English Units

The international inch by definition is 2.54 cm. A foot is 12 inches. A mile is 5280 feet.

One U.S. pint is 476.179 ml. A gallon is 8 pints.

One pound mass by definition is 453.592379 g [grams].

One pound force by definition is the weight of 1 pound mass at standard gravity [9.80665 m/s2], At the latitude of Paris, a 1 lb mass has a weight of 1 lb [force]. A spring scale measures weight. A balance scale measures mass.

Standard Pressure is 1 atmosphere, about 14.7 psi.

Air density at sea level and 59 F is about .002378 slugs / ft3.

One horsepower is equal to 375 lb-mph [pound-miles per hour] or about 746 watts.

Acceleration due to gravity in San Diego is about 32.16 ft/sec2 or almost 22 mph/second.

Nine degrees Fahrenheit (F) are equal to five degrees Celsius (C) [aka Centigrade]. Water freezes at 32 degrees Fahrenheit and boils at 212 degrees Fahrenheit at standard pressure.



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