Lectures on Physics has been derived from Benjamin Crowell's Light and Matter series of free introductory textbooks on physics. See the editorial for more information....

Less Common Metric Prefixes

The following are three metric prefixes which, while less common than the ones discussed previously, are well worth memorizing.

mega- M1066.4 Mm = radius of the earth
micro- μ10-610 μm = size of a white blood cell
nano- n10-90.154 nm = distance between carbon nuclei in an ethane molecule

Note that the abbreviation for micro is the Greek letter mu, μ - a common mistake is to confuse it with m (milli) or M (mega).

There are other prefixes even less common, used for extremely large and small quantities. For instance, 1 femtometer = 10-15 m is a convenient unit of distance in nuclear physics, and 1 gigabyte = 109 bytes is used for computers' hard disks. The international committee that makes decisions about the SI has recently even added some new prefixes that sound like jokes, e.g., 1 yoctogram = 10-24 g is about half the mass of a proton. In the immediate future, however, you're unlikely to see prefixes like "yocto-" and "zepto-" used except perhaps in trivia contests at science-fiction conventions or other geekfests.

g/This is amnemonic to help you remember the most important metric prefixes. The word little is to remind you that the list start swith the prefixes used for small quantities and build supward. The exponent changes by 3, except that of course that we do not need a special prefix for 100, which equals one.

Self-Check Suppose you could slow down time so that according to your perception, a beam of light would move across a room at the speed of a slow walk. If you perceived a nanosecond as if it was a second, how would you perceive a microsecond?
Answer A microsecond is 1000 times longer than a nanosecond, so it would seem like 1000 seconds, or about 20 minutes.

Last Update: 2010-11-11