You can’t have science without measurement, and measurement requires an agreed-upon set of standards. Almost the entire world uses the metric system, and in the United States we use the metric system for scientific work.The metric system is formally known as the International Standard System or SI system. It works by defining base units for elementary properties such as length and mass. Other units are made up of combinations of base units, and are called derived units. Many of the derived units are named after scientists who made major contributions to our understanding of that particular quantity. The units have abbreviations that are usually a single letter, such as m for meter or g for gram. Capitalization is important in notation, so get used to paying attention to it.
Units can be modified by putting a metric ## Common PrefixesThe metric system gives names to many different powers of ten, but in practice we only use a few. The engineering standard is to use every third power of ten, such as 10 Here are the commonly used prefixes, along with their abbreviations. Note that the capitalization is very important—M means Mega, but m means milli. The symbol for micro is the lower-case Greek letter mu (m).
## LengthThe base unit for length is the meter, which is just a little bit more than a yard. The meter has gone through several different definitions, each one more precise than its predecessors. It was originally intended to be one ten-millionth of the distance from the equator to the North Pole along a line of longitude passing through Paris. This is not a useful definition in practice, because it would be too difficult to measure, so they kept a metal bar in Paris that had two lines scribed into it. The distance between these lines was the international definition of the meter. In the 1960s the meter was defined in terms of wavelengths of light, and in the 1980s it was redefined in terms of the speed of light. ## VolumeVolume should not need its own unit, because it is based on length. If the base unit for length is a meter, then the unit for area should be a square meter or m A cubic centimeter is a commonly used volume that goes by several names. According tothe SI rules, a cubic centimeter should be abbreviated as cm
## MassThe base unit for mass is the
Today the unit for mass is defined by a standard kilogram mass, which is kept in Paris. A kilogram weighs about 2.2 pounds. |