Talk:SI derived unit

message: ===Litre===
what is a liter?
:Hmmm, seems to be a Cubic Decimeter. I think it would fit here. http://en.wikipedia.org/wiki/Liter
::"The litre (or liter in US) is a metric unit of volume. The litre is not an SI unit, but (along with units such as hours and days) is listed as one of the "units outside the SI that are accepted for use with the SI." The SI unit of volume is the cubic metre (m³)." So it seems like it's Metric, although not SI derived...
::: I would say the liter is indeed SI derived. There are 1000 liters in one cubic meter. Sauer202 (talk) 21:08, 10 September 2020 (UTC)
replies: text: I'm puzzled by its inclusion here, but BIPM claims that it's a derived SI unit.  But its definition is certainly not "K - 273.15".  You can't subtract a dimensionless number from a unit.  Rather, its definition is simply "K", and the quantity it measures is "temperature relative to 273.15 K". — Smjg (talk) 11:30, 13 April 2011 (UTC)
replies: text:  Thinking about it, it seems to me there is this definition of an SI derived unit: a measurement unit that is a multiplicative combination of zero or more SI base units.  Zero is the case of the radian and steradian; one is the case of the hertz, lumen and becquerel.  And the degree Celsius is an SI derived unit purely because it's another example of the same.  Does this seem right? — Smjg (talk) 00:12, 25 April 2011 (UTC)

text: Quinobi 21:16, 2 Oct 2004 (UTC)

text: Follow http://www1.bipm.org/en/si/derived_units/2-2-2.html and you will find that the dyne is 'not accepted' for use with SI (by omission). Contrast this with the deg Celsius which also has a defined relationship with an SI unit - kelvin, but this one is 'accepted for use' with SI. Dyne appears in the CGS system of units, which is very much less widely used than SI. Ian Cairns 21:36, 2 Oct 2004 (UTC)
replies: text:  Wouldn't the dyne still be an SI derived unit? 1 dyne = 10 micronewtons.21:14, 10 September 2020 (UTC)
thread_title: Non-SI metric units

message: what is a liter?
:Hmmm, seems to be a Cubic Decimeter. I think it would fit here. http://en.wikipedia.org/wiki/Liter
::"The litre (or liter in US) is a metric unit of volume. The litre is not an SI unit, but (along with units such as hours and days) is listed as one of the "units outside the SI that are accepted for use with the SI." The SI unit of volume is the cubic metre (m³)." So it seems like it's Metric, although not SI derived...
::: I would say the liter is indeed SI derived. There are 1000 liters in one cubic meter. Sauer202 (talk) 21:08, 10 September 2020 (UTC)
thread_title: Litre

message: As_I_Understand_It, degree Celsius is NOT an SI unit, the Kelvin is. Anyone know how to confirm / refute this? SGBailey 10:34 Dec 12, 2002 (UTC)
The table suggests the "Celsius" is an unofficial unit of temperature. Shouldn't that be the "degree Celsius"? — Preceding unsigned comment added by 142.30.227.14 (talk • contribs) 00:03, 29 April 2010 (UTC)
replies: text: I'm puzzled by its inclusion here, but BIPM claims that it's a derived SI unit.  But its definition is certainly not "K - 273.15".  You can't subtract a dimensionless number from a unit.  Rather, its definition is simply "K", and the quantity it measures is "temperature relative to 273.15 K". — Smjg (talk) 11:30, 13 April 2011 (UTC)
replies: text:  Thinking about it, it seems to me there is this definition of an SI derived unit: a measurement unit that is a multiplicative combination of zero or more SI base units.  Zero is the case of the radian and steradian; one is the case of the hertz, lumen and becquerel.  And the degree Celsius is an SI derived unit purely because it's another example of the same.  Does this seem right? — Smjg (talk) 00:12, 25 April 2011 (UTC)
thread_title: Celsius

message: I dont see the dyne  (symbol: dyn) mentioned here or on the force page. It appears to have a defined relationship with the newton. Is it a bastard unit of measure?
:Quinobi 21:16, 2 Oct 2004 (UTC)
replies: text: Follow http://www1.bipm.org/en/si/derived_units/2-2-2.html and you will find that the dyne is 'not accepted' for use with SI (by omission). Contrast this with the deg Celsius which also has a defined relationship with an SI unit - kelvin, but this one is 'accepted for use' with SI. Dyne appears in the CGS system of units, which is very much less widely used than SI. Ian Cairns 21:36, 2 Oct 2004 (UTC)
replies: text:  Wouldn't the dyne still be an SI derived unit? 1 dyne = 10 micronewtons.21:14, 10 September 2020 (UTC)
thread_title: Dyne

message: I have started changing some of the math formulas to use <math> constructs. I think this looks much better, and is not much more difficult to edit (see Wikipedia:TeX markup). If nobody objects, I will finish this off sometime soon. I agree that the freeform table looks pretty bad, and the html table isn't much better. I don't think the html table is too difficult to edit, but maybe I will format it in a way that makes it easier for people to understand how to edit. Or maybe I'll make my own attempt at a freeform table. We'll see... --HN 21 May 2003
:Why not use Wikipedia table markup instead? (Random832 01:05, 14 Jun 2004 (UTC)
replies: text: Does anyone else find the page extremely s..l..o..w.. to load - principally because of the huge amount of maths involved in simple text fields? I would like to replace the maths by text, with a suitable appearance / emphasis. Does anyone have any objections, please? Ian Cairns 00:16, 8 Nov 2004 (UTC)
thread_title: Maths notation

message: I propose that this be merged to Degree Celsius#Conversions.  Jimp 14Oct05
:Keep it here.  (It is already there, isn't it?)  It belongs here, because unlike any of the other conversions, this is a conversion within the International System of Units between two different SI units (or two different names for the same SI unit, depending how you look at it).  It is quite relevant to the structure and usage of SI.  Gene Nygaard 08:34, 14 October 2005 (UTC)
replies: text: I still think there is a huge difference between giving the relationship of one SI unit to another SI unit, as compared to giving a conversion factor between an SI unit and a non-SI unit.  There aren't going to be many of these; even the newton metre and the joule, which are both listed here, while dimensionally equivalent are used to measure different quantities.  Degrees Celsius and kelvins measure the same quantity. That N·m to J relationship, of course, is pretty trivial in any case, not warranting the slightly more detailed explanation for the temperature readings.  Gene Nygaard 00:50, 21 October 2005 (UTC)

text: Sure they can. The triple point of water is at 0.01 °C. --DrTorstenHenning (talk) 08:16, 18 July 2008 (UTC)

text: But the degree Celsius is a derived unit. --DrTorstenHenning (talk) 08:17, 18 July 2008 (UTC)
thread_title:  Conversion between kelvins and degrees Celsius 

message: Shouldn't the "Expression in terms of SI base units" be cd ^ -1 as it is 1/cd? --I hate to register 12:43, 31 July 2006 (UTC)
thread_title:  Possible error in lumen? 

message: Would it not be better and clearer to quote the Newton as being kg.m/s^2 rather than m.kg/s^2? After all Force is usually quoted as F=ma (mass x acceleration). Similar with Pascals.  —Preceding unsigned comment added by 195.195.173.31 (talk) 15:05, 6 November 2007 (UTC)
replies: text: No, the units used in definitions are standardised in the order m, kg, s, A, K, mol, cd (not sure why). Hence odd-looking things like m-2∙cd. 212.137.63.86 (talk) 11:18, 6 August 2008 (UTC)
replies: text: They're in that order for the first table "Derived units" but the second table "Other units" puts kg before m. I think the second table should be corrected.  —Preceding unsigned comment added by 131.107.0.77 (talk) 23:16, 9 February 2010 (UTC)
thread_title:  Units for Newton and Pascal query 

message: 212.137.63.86 (talk) 11:19, 6 August 2008 (UTC)
replies: text: Indeed, the Kelvin is a base unit, not derived. Could anyone comment on why it appears on this page ? Update: I went ahead and changed it to the definition of the degree Celcius, since that is most likely what was intended.     66.130.179.31 (talk) 04:07, 7 August 2008 (UTC)
thread_title:  What the heck is kelvin doing here!? 

message: Correct me if I'm wrong, but I do not believe that E should be here.  It's the symbol for the electromagnetic field, but not a unit of magnitude.  It's comparable to T(time) and L(length) as opposed to being comparable to s(second) or kg(kilogram).  I will go ahead and remove it on the grounds that it doesn't belong here.  Feel free to revert back if I am wrong.  I am a student and not a scientist.  -70.119.126.195 (talk) 04:44, 22 November 2008 (UTC)
thread_title:  E 

message: Specific Energy Density is the product of the specific energy of a material times its energy density.  The higher the number, the more potential energy is contained in that substance.  As the typical units of Specific Energy are m2/s2 or J/kg, and of Energy Density are kg/m·s2 or J/m3, so the product is equivalent to kg·m/s4 or J·J/kg·m3.  Unfortunately there is no SI unit for this, but it is the best way of classifying a material by its energy content, since lower mass or less volume will increase the overall number.  It's a pity there's no SI derived unit for this concept.  May I name it?  Surely I'm not the first to discuss it?  But can we call it Jacobs?  :)
--TimeHorse (talk) 19:18, 4 January 2011 (UTC)
thread_title:  Specific Energy Density 

message: I suggest adding 7 columns to the table: m, kg, s, A, K, Cd and mol, the values in each of these columns will be the exponent of the SI unit or 0 if that unit does not form part of the definition.  For instance, Hertz would be 0, 0, -1, 0, 0, 0, 0; Newtons would be 1, 1, -2, 0, 0, 0, 0; Lumen would be 0, 0, 0, 0, 0, 1, 0; Volt would be 2, 1, -3, -1, 0, 0, 0; etc.
--TimeHorse (talk) 19:24, 4 January 2011 (UTC)
replies: text: I'm not sure whether such a table would be useful.  But if we do have it, I think it would be clearer if we represented 0 by a blank cell. — Smjg (talk) 09:14, 29 April 2011 (UTC)
thread_title:  Sort by power of SI unit 

message: I propose to swap the order of the tables (to match the SI Brocure), so that Table 1 gives examples of the unlimited number of derived units and Table 2 is a list of specially-named derived units (so that the article discusses the general before the particular)
Adamtester (talk) 00:38, 14 January 2011 (UTC)
thread_title: Rearranging this article

message: radians somehow cannot be expressed wouldn't that make it a base unit?  —Preceding unsigned comment added by 79.71.100.247 (talk) 22:56, 2 April 2011 (UTC)
replies: text: The radian is considered to be equal to 1, because an angle is essentially just a ratio of arc length to radius. — Smjg (talk) 11:08, 28 April 2011 (UTC)

text: For what it's worth, some older books give the radian and steradian as base units.  My guess is that BIPM/CIPM/CGPM at the time didn't consider them to be fundamentally different from the other base units, even though each is defined in the most natural way possible.  Then they were reclassified as supplementary units as an acknowledgement of this subtle difference.  It was later again they decided that, since a radian is really just a metre (of arc length) per metre (of radius), it is really a derived unit, even though all the units that make it up cancel each other out.  Similarly with the steradian, which is a square metre (of surface) per metre (of radius) squared.  But it does lead to such oddities as that the lumen is, when expressed in terms of SI base units, just a candela. — Smjg (talk) 20:26, 29 April 2011 (UTC)
replies: text: I understand that Radians are ratios and aren't dependent on radius but arc length, but an example is good.  — Preceding unsigned comment added by 195.194.89.13 (talk) 13:16, 11 March 2013 (UTC)
thread_title:  what does dimensionless mean? 

message: The table stated incorrectly that 1 °C = 1 K - 273.15.  What is meant is that 1 °C = 1 K, but that the degree Celsius is used for reporting temperatures relative to 273.15 K. Dondervogel 2 (talk) 07:31, 5 January 2015 (UTC)
thread_title:  corrected error in degree Celsius equivalence 

message: N-m is for Torque as well as Energy too. 
Should not that too be added in the table?
thanks!
~"aGastya"  ✉ let’s talk about it :) 11:50, 18 February 2015 (UTC)
thread_title: Newton Metre (or meter as per US)

message: second inverse is there in table of "Named units derived from SI base units"
metre inverse is names in table of "Some SI derived units"
Why so?
both of them should be in a same table, isn't it?
And then also "Angular Frequency" is also missing in the table (second inverse)
Thanks
~"aGastya"  ✉ let’s talk about it :) 11:58, 18 February 2015 (UTC)
thread_title: Meter inverse vs Second inverse

message: According to [], nautical miles (and by extension, knots) are acceptable non-SI units. Why aren't they on the page or the template? Is this an example of systemic bias against imperial units?  — Preceding unsigned comment added by 161.149.102.86 (talk) 06:20, 8 July 2016 (UTC)
replies: text: Neither of the 2 units you mention are SI derived units so I see no compelling reason to include them in an article entitled 'SI derived units'. If you disagree there's nothing to stop you editing the page.  Dondervogel 2 (talk) 23:06, 8 July 2016 (UTC)
thread_title: What about Nautical Mile?

message: The 'expression in terms of SI base units' for lumen per watt 'm−2⋅kg−1⋅s3⋅lm' should be changed into 'm−2⋅kg−1⋅s3⋅cd' in order to be consistent with the SI base unit table.  — Preceding unsigned comment added by 176.127.191.90 (talk) 08:47, 10 September 2016 (UTC)
thread_title: lumen per watt

message: An editor has asked for a discussion to address the redirect Planck electric potential. Please participate in the redirect discussion if you wish to do so.  signed, Rosguill talk 17:36, 8 April 2020 (UTC)
thread_title:  "Planck electric potential" listed at [[Wikipedia:Redirects for discussion|Redirects for discussion]] 

message: Why are all the surname units in lowercase? Convention dictates that Newton, Ohm, etc. be capitalized. --98.216.104.10 (talk) 14:43, 15 August 2020 (UTC)
replies: text: The purpose is to distinguish between the name of a unit (eg watt) and the name of the person it was named after (Watt). Dondervogel 2 (talk) 19:55, 15 August 2020 (UTC)
thread_title:  Capitalization 

message: Maybe move to SI derived units. It just sounds better.
2A02:C7D:3FB0:300:E895:45DB:31:1A0D (talk) 18:40, 13 October 2020 (UTC)
thread_title: Possible Move

message: I think 1 C is exactly 1/(1.602176634×10−19), which is 1/(unit of elementary charge: e). So how can it be a derived unit?
I think necessary changes in effect since 20 May 2019 of SI is not reflected in this article... JSoos (talk) 11:10, 6 November 2020 (UTC)
thread_title:  Coulomb 

message: In the chart about meters per second, m/s is described as speed and velocity. From a bit of cursory research, velocity is meters per second (m/s), and speed is velocity without regard to direction, or the absolute value of velocity (|m/s|). Should other people agree, should this be changed or noted? Saltedcoffii (talk) 13:19, 21 November 2022 (UTC)
replies: text: m/s can be used as a unit of speed or velocity. What change are you suggesting? Dondervogel 2 (talk) 13:52, 21 November 2022 (UTC)
thread_title:  Speed vs velocity 

message: JPF 2023-01-11: I'm not sure - I see this page for the first time - but please take a look for units of
- "magnetic moment": Equal to "magnetic dipole moment" with unit J/T ? Both quantities show different base units, but refer to the *same* Wikipedia article ...
- "magnetic rigidity": I don't know what that is, but the referred article names its unit: Volt, and later then (indeed) T*m ... The rigidity article seems irritating to me (I'm no particle physicist); nevertheless, please check the unit in *this* article. 91.16.152.248 (talk) 21:24, 11 January 2023 (UTC)
thread_title:  Magnetic moment, magnetic rigidity - Wrong units ?