Talk:Birch's law

a(M) as a function
Writing it as aM gives the erroneous impression that it is a constant (a) times the average atomic mass (M), when a is in fact a function of M. Birch's law is linear since it is of the form y = mx + b, but a(M) is the y-intercept and is different for different values of M.  For example, Birch states, "The function a(m) is best determined for m ~ 21 ; a small group of points at m ~ 24 gives another value, and finally a scattered group of iron and titanium oxides indicate roughly the value for m ~ 30. Estimates of a(m) are shown in Table 3," where Table 3 gives a(21) = -2.55, a(25) = -5.7, and a(30) = -8.6 (units intentionally left out). Le Duf (talk) 02:16, 22 May 2012 (UTC)


 * Looks like you're right. You'd think that a college geophysics text would get it right. Thanks for pointing that out! RockMagnetist (talk) 15:50, 28 May 2012 (UTC)


 * My copy of Fowler is buried away somewhere, so I don't know how she treats it. Poirier does get it right, as you cited.  Le Duf (talk) 17:01, 28 May 2012 (UTC)

2 Feb edit
The new line seems redundant to me. Any thoughts to removing it? — Preceding unsigned comment added by Le duf (talk • contribs) 01:46, 4 February 2015 (UTC)

Possible articles to help improve the page
Daniele AntonangeliTetsuya KomabayashiYingwei Fei. Simultaneous sound velocity and density measurements of hcp iron up to 93 GPa and 1100 K: An experimental test of the Birch's law at high temperature. Earth and Planetary Science Letters. 15 May 2012, Vol.331. http://www.sciencedirect.com/science/article/pii/S0012821X12001471

Jung-Fu Lin1, Wolfgang Sturhahn, Jiyong Zhao, Guoyin Shen,Ho-kwang, Mao Russell J. Hemley. Sound Velocities of Hot Dense Iron: Birch's Law Revisited. Science 24 June 2005. Vol. 308 no. 5730 pp. 1892-1894. http://m.sciencemag.org/content/308/5730/1892.short — Preceding unsigned comment added by 204.29.102.227 (talk) 16:51, 24 February 2015 (UTC)

Applications of Birch's Law
Birch's Law is used for a variety of different things in geophysics. It can be used in the discussion of geophysical data. Birch's Law is used in forming compositional and mineralogical models of the mantle by using the channge in the velocity of the seismic wave and it's relationship with a change in density. It is used in determining chemical similarities in the mantle and the discontinuities of the transition zones. Birch's Law can also be employed in the calculation of an increased of velocity due to an increase in density — Preceding unsigned comment added by Mhunter (talk • contribs) 18:55, 31 March 2015

Edits/ Critique
Thank you. I will look over the awkward sentence and try to rephrase it. I am thing about adding a diagram explaining the experimental set up. Mhunter2 (talk) 11:14, 23 April 2015 (UTC)

Well done so far! It would be nice to see another picture (like a graph, perhaps) but I know for this subject it is a little difficult. Also, the sentence, "It can be used in the discussion of geophysical data" seems out of place or too much like a filler sentence. Maybe not needed at all. Other than that, good job. NealeyS (talk) 02:55, 23 April 2015 (UTC)

I like your page! I see some good information and I like the equation. One thing I recommend is, also Nealey said, maybe it is helpful to put some pictures or images to show how the experiment is going on in the Solving Birch's law experimentally section. Tomoyuki6 (talk) 22:55, 27 April 2015 (UTC)

Any background on who the experimentalist is that actually discovered this effect? When did this start being used by geophysicits to chart chemical compositions?68.35.72.13 (talk) 03:19, 28 April 2015 (UTC)

Tomo, I think adding a picture of how the experiment works would be helpful. Thank you. As far as the background on the experimentalist who discovered Birch's Law, it was Francis Birch in 1961. I have him referenced in the opening of the article, but I did not want to go too much in depth on him because he has his own page. I don't want to seem like I am just coping what is written on his wiki page. Mhunter2 (talk) 23.124.64.27 (talk) 12:31, 28 April 2015 (UTC)

Velocity units
In the table of velocities provided, are the velocity units km/s? They should probably be labeled right? --2607:B400:26:0:BC1C:455A:984E:9C78 (talk) 18:47, 9 August 2017 (UTC)
 * Same question by me ... And shouldn't p be lowercase? --User:Haraldmmueller 12:45, 21 October 2020 (UTC)

Proposed changes
This is not my field and i have not read the references, but i think this first sentence is clearer: Birch's law establishes a linear relation between compressional wave velocity v_p and density ρ {\displaystyle \rho } \rho for rocks and minerals:

...same equation...

where M_avg is the average formula mass of the rock, a is a function of M_avg, and the function a is assumed to be constant with respect to other variables.[1]

This addresses these simple questions from naive readers (eg, me a few minutes ago): What does "rocks and minerals of a constant average atomic weight" mean ? Minerals are crystalline and can be composed of atomic as well as molecular ions. Is the "constant" modifier misplaced? Perhaps this is common geophysical lingo (?), but some examples might go a long way in clarifying this.

Also i think this would pave the way for a rewrite of the section "Shortcomings with Birch's Law". I think that section is trying to indicate that the function a(M_avg) is in fact not independent of other variables because crystalline phases are dependent on pressure. sbrozell0 May 15, 2018
 * Thanks for the suggestion. I have used something similar for the lead, and added the section Example to give a numerical example. I hope that helps. RockMagnetist(talk) 16:26, 22 May 2018 (UTC)