Are There Prefixes for Decimal Places Between the Commonly Used Ones?

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Discussion Overview

The discussion revolves around the existence of prefixes for decimal places that fall between the commonly used SI prefixes, particularly for values like 10^-4 and 10^-7. Participants explore the structure of SI prefixes and their application in various contexts, including historical perspectives on unit definitions.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Debate/contested, Historical

Main Points Raised

  • Some participants note that SI prefixes exist for certain powers of ten, but primarily reference powers of 1000, leaving gaps for decimal places in between.
  • One participant mentions that for 10^-4, it is common to express values as ".1 milli" or "100 micro," suggesting a workaround rather than a formal prefix.
  • Another participant introduces the angstrom as an unofficial unit for 10^-10 meters, indicating that it does not fit within the SI system.
  • Discussion includes the transition from cgs to mks units, with references to Gauss and Tesla as examples of this shift.
  • Concerns are raised about the kilogram being the base unit of mass, with some participants questioning why the gram was not used instead, citing historical context and common usage.
  • Historical context is provided regarding the transition from centimeter/gram/second (cgs) to meter/kilogram/second (mks) and the complications that arose during this period, particularly in electromagnetism.
  • Participants express frustration over the lack of a new name for the kilogram, suggesting that it complicates understanding in everyday contexts.

Areas of Agreement / Disagreement

Participants generally agree that there are gaps in the SI prefix system for certain decimal places, but multiple competing views exist regarding the implications and historical reasons for these gaps. The discussion remains unresolved regarding the best approach to address these gaps and the rationale behind the use of the kilogram as a base unit.

Contextual Notes

Limitations include the lack of formal prefixes for certain decimal values, dependence on historical definitions, and unresolved questions about the transition from cgs to mks units.

EebamXela
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Are there prefixes for the decimal places in between the ones that are commonly used?

Like for 10^-4, or 10^-7?
 
Physics news on Phys.org
There are SI prefixes for 100, 10, 1/10, and 1/100. Above/below that, all prefixes reference powers of 1000.
 
1000m 10n Prefix Symbol Since[1] Short scale Long scale Decimal
10008 1024 yotta- Y 1991 Septillion Quadrillion 1 000 000 000 000 000 000 000 000
10007 1021 zetta- Z 1991 Sextillion Trilliard 1 000 000 000 000 000 000 000
10006 1018 exa- E 1975 Quintillion Trillion 1 000 000 000 000 000 000
10005 1015 peta- P 1975 Quadrillion Billiard 1 000 000 000 000 000
10004 1012 tera- T 1960 Trillion Billion 1 000 000 000 000
10003 109 giga- G 1960 Billion Milliard 1 000 000 000
10002 106 mega- M 1960 Million 1 000 000
10001 103 kilo- k 1795 Thousand 1 000
10002/3 102 hecto- h 1795 Hundred 100
10001/3 101 deca- da 1795 Ten 10
10000 100 (none) (none) NA One 1
1000−1/3 10−1 deci- d 1795 Tenth 0.1
1000−2/3 10−2 centi- c 1795 Hundredth 0.01
1000−1 10−3 milli- m 1795 Thousandth 0.001
1000−2 10−6 micro- µ 1960[2] Millionth 0.000 001
1000−3 10−9 nano- n 1960 Billionth Milliardth 0.000 000 001
1000−4 10−12 pico- p 1960 Trillionth Billionth 0.000 000 000 001
1000−5 10−15 femto- f 1964 Quadrillionth Billiardth 0.000 000 000 000 001
1000−6 10−18 atto- a 1964 Quintillionth Trillionth 0.000 000 000 000 000 001
1000−7 10−21 zepto- z 1991 Sextillionth Trilliardth 0.000 000 000 000 000 000 001
1000−8 10−24 yocto- y 1991 Septillionth Quadrillionth 0.000 000 000 000 000 000 000 001

Shamelessly taken from wiki.
 
EebamXela said:
Are there prefixes for the decimal places in between the ones that are commonly used?

Like for 10^-4, or 10^-7?

None of which I am aware. For 10-4, you just say ".1 milli" or "100 micro," and on like that.
 
There are a few odd ones, for example 10^-10 m is an angstrom, or 1 Tesla = 10000 Gauss.
 
The angstrom is an unofficial 'convenient' unit like the barn so doesn't fit in the SI series.
The Gauss / Tesla is because of the switch from cgs to mks units.

The centi / hecto were just because people had traditionally been used to working in units of 100 - at least outside Britain!

The annoying one is the kilogram, either the gram should have been redefined (messy) or a new name chosen so that the base unit of mass didn't have a prefix.
 
mgb_phys said:
The annoying one is the kilogram, either the gram should have been redefined (messy) or a new name chosen so that the base unit of mass didn't have a prefix.

I have always wondered this! All units (at least the ones I ever saw) in the SI system use the kilogram instead of the gram. For example, a Newton is a kilogram-meter per second^2.
Why not a gram-meter per second^2? All other units are the 'base' units without kilo, milli, whatever as a prefix...

Is it just because the kilogram is so common (where I live anyway), or is there another reason?
 
Originally units were defined in terms of centimetre/gram/second, I have no idea why the cm was chosen except that it was a convenient human size unit like the inch.
It took around 100years before MKS replaced them in the 1950s

Unfortunately this was a 100 years in which quite a lot was invented - including all of electromagnetism. Just to make it even more fun, a lot of the electromagnetic units differ by factors like 2pi and 4pi between cgs and mks as well as the factors of 1000 you would expect. Although pretty much textbooks are now mks, a lot of papers especially in astronomy and chemistry use cm or 1/cm.

Just like a Tesla is a new name rather than calling the base unit 10KGauss they really should have come up with a new name for the kilo.
They didn't because it is the unit most widely used outside of science, so although Gauss and Tesla are used together in electrical engineering today it would be very confusing in shops if you had grams and whatever the new unit was called ( and pounds!)
 

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