Units,Dimentions, Measures and calabration.


CHEMTUTOR
Measurement is the most useful form of description in science. Often the most useful measurements are those that have a number and a unit, such as ‘12.7 inches.' Here '12.7' is the number and 'inches' is the unit. This unit of inches in the example is one of the common units in the dimension of length. A number, then, is an expression in numerals. A unit is a recognized way to divide the essence of a dimension for measurement, and a dimension is a measurable physical idea. Here is a bit of advice you can overlook only at your peril: To become fluent in the subject you should memorize the basic background of information. The following units, dimensions, and measures are so basic to the study of Chemistry that you could always help yourself by memorizing these. The real test of whether you know this well enough is to recognize the dimensions of any measurement and know its symbol and magnitude from the unit alone.
DIMENSIONS, UNITS, AND SYMBOLS
Notice the symbols of the dimensions as they would be used in formulas. The basic metric symbol or the symbol of the most used metric unit is listed after the metric units.
DIMENSION SYMBOL METRIC UNITS SYMBOL “ENGLISH” UNITS
LENGTH S, l, d, r meter (+m.p.) m Ft, in,Yd, mi, etc.
AREA A sq.meter, etc,hectare m2 sq.Ft, etc., acre
VOLUME V cu.meter, etc., liter m3, L cu.Ft,cu.in,etc.,gal,Floz.
TIME t sec (+m.p.) sec,min,hr,day,yr,etc.(both metric & English)
MASS m Kilogram (+ m.p.), AMU kg (slug, rarely used)
FORCE (weight) F, Fw Newton (+ m.p.) N Pound (#), Oz, etc.
VELOCITY v meter/sec,KPH,etc m/sec Ft/sec, MPH, etc.
ACCELERATION a meter/sec.sq., etc. m/sec2. Ft/sec sq., etc.
PRESSURE P N/sq.m, atm.,Pa atm,Pa* #/sq.in (PSI), inHg, etc.
DENSITY D g/cc, Kg/liter, etc. g/cc #/cu.Ft, #/gal, etc.
TEMPERATURE T Celsius or Kelvin °C Fahrenheit or Rankine
ENERGY E Joule (+ m.p.) J foot-pound
HEAT Q calorie (+ m.p.) cal BTU (British Thermal Unit)
CONCENTRATION C** gram/L, mol/L, Molar M (#/gal or #/cu.ft, rare)
Abbreviations: Ft = foot, in = inch, AMU = atomic mass unit, KPH = kilometers per hour, MPH = miles per hour,
gal = gallon, PSI = pounds per square inch, cc = cubic centimeter, inHg = inches of mercury, Pa = Pascal
m.p. = metric prefixes, cu. = cubic, sq. = square, atm = atmosphere.
*The unit Pa, for Pascal, is a unit of pressure that is the standard unit for the SI system, the MKS system in the metric measurements. The unit of Pascal, however, is rarely used in chemistry. Instead, the unit "atm," for "atmosphere," is still most used in chemistry.
**The symbol "B" is now the official symbol for concentration in the SI, but there are still chemistry texts using the "C" as is shown here."
The table above lists almost all the dimensions you will need in this course, the symbol for each dimension as it will be used in common formulas, and the units of each dimension. Notice Chemtutor has two systems of measurement displayed that you should know. There are really two commonly used metric subsystems. Most chemistry texts will use the MKS system (meter, kilogram, second) rather than the less-used CGS (centimeter, gram, second) system. A system is defined by its basic measure of distance, mass, and time.We will use the MKS system, also called the S.I., or International System. The symbol for only the basic unit of each dimension in the metric system is on the list.
METRIC SYSTEM vs. "ENGLISH SYSTEM"
The metric system typically uses only one root word for any basic dimension such as for length, the meter. All the metric units of length use the root word 'meter' with the metric prefixes in the next table. Our common system in the United States is not really a system, but is a thrown-together mess of measurements with no overriding order. Chemtutor, as does most of the United States, calls this group of measurements the “English system.” While calling it that is a considerable slander on the English people, the United States and Liberia are the only nations on earth to still cling to it. Chemtutor thinks that the English system makes a fine learning tool, along with being wonderfully poetic. You will want to know how to relate the English System to the metric system. Particularly notice the large number of units of length in the English system. This is only a small number of the common ones. We regularly use fathoms to measure depth in water and furlongs to measure distance in horse racing. There are many little-used English length units such as the barleycorn (one third of an inch) that may be picturesque, but are not used today. Notice that we define the