- METRIC SYSTEM (also called SI):
For over 200 years, scientists around the world have used the metric system or
"Systeme Internationale" (SI).
In all countries (except the United States), metric units are also used in general commerce.
The metric system is based on these basic units, internationally agreed upon:
- Meter, originally defined as 1/10,000,000 of the distance from the North Pole to the Equator
on the meridian running through Paris.
- Gram, the base unit of mass.
- Second, the base unit of time.
- Four other base units: the Kelvin for absolute temperature, the candela for
light intensity, the mole for chemical quantities, and the Coulomb for electrical charge.
- MULTIPLES of the base units use a standard set of abbreviations, based on the Greek names for powers of ten.
The most important of these is the prefix "Kilo-", which always means 1000 times the base unit.
Smaller units use standard abbreviations based on Latin names.
The two most important of these are "centi-"
for 1/100 of the base unit, and "milli" for 1/1000 of the base unit.
The complete set of prefixes for metric units is shown on this chart.
All bigger and smaller units are based on powers of ten, so conversions within the metric system are easy because you only need to move the decimal point!
Liter: An important derived unit, the liter, is defined as a volume exactly 10 cm (=0.1 m) by 10 cm by 10 cm.
The gram was originally defined as the mass of one milliliter (or 1 cubic centimeter) of water.
NOTE: A milliliter (mL) is the same as a cubic centimeter (cm3).
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- SOME CONVERSIONS:
The inch is now defined as exactly 2.54 centimeters or 0.0254 meters. A meter is approximately 39.37 inches.
The pound is 454 grams when measured at the Earth's surface.
A quart is about 0.908 liters, so a liter is about 1.1 quarts.
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- Temperature is peculiar:
For most purposes, the commonly used temperatures are in degrees Celsius (also called "centigrade").
The Celsius temperature is
always equal to the absolute (Kelvin) temperature plus 273 degrees: C = K + 273
Fahrenheit temperatures are not used in science. Converting between Fahrenheit and Celsius temperatures uses these formulas:
oF = oC x1.8 + 32
oC = 5/9 ( oF - 32)
The freezing point of water is 0o C = or 32o F
The boiling point of water is 100o C = or 212o F
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