Talk:Svedberg

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Error found

From an email to helpdesk:

"Your Wikipedia article entitled "Svedberg" states that "The sedimentation rate or coefficient of a particle or macromolecule is computed by dividing the constant speed of sedimentation (in m/s) [i.e., in meters/second] into the acceleration applied [(in m/s/s)]." The actual mathematical expression that was included within the second set of parentheses in the preceding sentence is the expression that one would read aloud as "meters per second squared." This e-mail program does not enable the user to type a superscript "2" after the "s" in the denominator, so this user typed "m/s/s." However, if one divides the speed of sedimentation, m/s, into the acceleration applied, m/s/s, one obtains 1/s instead of s. The article says that "The result [of the division] has the dimensions of a unit of time and is expressed in svedbergs." The article says that one svedberg is exactly 10 to the minus 13 power s. Again, this e-mail program does not enable the user to type superscript symbols. If a svedberg is expressed in s, a svedberg cannot be calculated by dividing m/s into m/s/s. Would you please clarify and/or correct the stated method of computing the sedimentation rate or coefficient of a particle or macromolecule?" --James W. Frederiksen, MD

Someone please give the correct derivation. --maru (talk) contribs 06:01, 27 January 2006 (UTC)[reply]

The equation is s = v/(W^2 r)

where v is velocity of sedimentation

     w is rate of rotation
     r is distance from the axis of rotation

The dimensions can be calculated from this, but im not certain about the units —Preceding unsigned comment added by 84.71.66.130 (talk) 09:14, 3 April 2008 (UTC)[reply]

Incomprehensible

This page is nearly incomprehensible -- and I am a professional physicist! I will attempt to clean it up in the near future, but in the short term, can someone make it clear whether, in the first paragraph, the Svedberg is $10^{-13}$ s, or whether it is on the order of $10^{-13}$ s or whether it is conventionally reported in units of $10^{-13}$ s? I think it must be on the order of $10^{-13}$ s. -- David W. Hogg 21:45, 20 April 2007 (UTC)[reply]

Clarifications

I agree that the article was mostly incomprehensible to someone who is not at least familiar with the basic physics of sedimentation processes. I'm writing a chapter on centrifugation for a first-year biochemistry reader, so did some background research this week. I've tried to clarify some points by explaining what is meant by applied acceleration, and adding some formulas and references. More work may be needed though. Perhaps the article should be renamed Sedimentation coefficient, or split into two separate articles (one on the unit and one on the coefficient). Moreover, it would be nice to have an explanation of why one would want to calculate or measure the sedimentation coefficient of a particle. I know of at least two reasons: 1) To be able to estimate sedimentation time when the s of a particle is known (see the article clearing factor, which I just created), and 2) to derive physical properties of the particle by measuring s (in a known medium). I'm afraid I do not know enough about analytical ultracentrifugation to say how to do the latter though. :-) Anyone? Levien van Zon (talk) 20:19, 11 September 2008 (UTC)[reply]

Split into two articles

OK, this was getting too messy. This article should be about the unit svedberg, not about the sedimentation coefficient that it is used to measure -- these are two separate things. So I removed the redirect from the sedimentation coefficient article, moved a lot of the content from this article to that one, and cleaned up both articles a bit. It seemed a logical thing to do, I hope everyone agrees... Lvzon (talk) 23:35, 11 September 2008 (UTC)[reply]

I think the Svedberg article is not understandable without a basic description of the definition of the sedimentation coefficient. I think it is clearer if both are united under the sedimentation coefficient headline, with a subheadline dealing with the Svedberg unit. Any more opinions? NiolonGER (talk) 10:54, 1 August 2010 (UTC)[reply]

Scope

"By convention, all sedimentation coefficients are expressed in the Svedberg units." is plain wrong. They are certainly not used to describe sedimentation of grains of sand in the ocean, for example. —DIV (120.19.213.255 (talk) 11:26, 11 June 2016 (UTC))[reply]

Correction

The Svedberg is a unit for the sedimentation coefficient, which can be determined from the sedimentation rate. Sedimentation rate has units of distance/time, while the Svedberg has units of time. See the wikipedia page for Sedimentation coefficient for the relationship between sedimentation coefficient and sedimentation rate. Siegele (talk) 20:19, 2 September 2018 (UTC)[reply]

Capitalisation

An SI unit name (not its symbol) always starts lowercase (metre, microsecond), even if it is named after a person (watt, coulomb), unless it starts a sentence. Why is it not the case for Svedberg? Is it because it is not an SI unit? Petr Matas 00:23, 11 January 2022 (UTC)[reply]

The answer seems to be that we must distinguish Svedberg unit (which is capitalized because the word Svedberg refers to the scientist) from svedberg (which is not because the word svedberg refers to the unit). Compare it to degree Celsius vs kelvin. I am going to fix the article. Petr Matas 20:02, 13 January 2022 (UTC)[reply]