User:Tohline/Appendix/Equation templates

Key Equations

Each of the equations displayed in the Table, below, encapsulates a physical concept that is fundamental to our understanding of — and, hence our discussion of — the structure, stability, and dynamics of self-gravitating systems. The pervasiveness of these physical concepts throughout astrophysics is reflected in the fact that the same equations — perhaps written in slightly different forms — appear in numerous published books and research papers. When attempting to understand the physical concept that is associated with any one of these mathematical relations, it can be helpful to read how and in what context different authors have introduced the expression in their own work. The Table offers a guide to some parallel discussions that have appeared in published texts over the past 5+ decades in connection with a selected set of key physical relations.

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Parallel References
§ no. and (Eq. no.)

Template_Name

Resulting Equation

C67

LL75

BT87

KW94

P00

EQ_Continuity01

Continuity Equation:

<math>\frac{d\rho}{dt} + \rho \nabla \cdot \vec{v} = 0</math>

§I.1
(1.2)
Note

I: §8.5
(8.45)

EQ_Euler01

Euler Equation:

<math>\frac{d\vec{v}}{dt} = - \frac{1}{\rho} \nabla P - \nabla \Phi</math>

§I.2
(2.1)
Note

I: §8.5
(8.48)

EQ_FirstLaw01

1^st Law of Thermodynamics:

<math>T \frac{ds}{dt} = \frac{d\epsilon}{dt} + P \frac{d}{dt} \biggl(\frac{1}{\rho}\biggr)</math>

§I.2
(2.5)
Note

I: §8.5
(8.53)

EQ_Poisson01

Poisson Equation:

<math>\nabla^2 \Phi = 4\pi G \rho</math>

§I.3
(3.5)
Note

I: §10.2
(10.1)
Note

EQ_EOSideal00

EQ_EOSideal0A

Ideal Gas Equation of State:

<math>~P_\mathrm{gas} = \frac{\Re}{\bar{\mu}} \rho T</math>

§II.1
(1)
Note

§IX.80
(80.8)
Note

I: §5.6
(5.91)

EQ_EOSideal02

<math>~P = (\gamma_\mathrm{g} - 1)\epsilon \rho </math>

EXAMPLE: Suppose you want to gain a better understanding of the origin of the ideal gas equation of state, the definition of the gas constant <math>~\Re</math>, or how to determine the value of the mean molecular weight <math>~\bar{\mu}</math> of a gas. According to the Table, you will find a discussion of the ideal gas equation of state: near Eq. (1) in §II.1 of Chandrasekhar (1967); near Eq. (80.8) in §IX.80 of Landau & Lifshitz (1975); near Eq. (5.91) in Vol. I, §5.6 of Padmanabhan (2000); etc. A "note" (linked to a comment at the bottom of this page) appears along with a table entry if the relevant equation in the cited reference contains notations or symbol names that differ from the equation as displayed here.

Key Parallel (Printed Text) References (spanning 5+ decades)

[C67] Chandrasekhar, S. 1967 (originally, 1939), An Introduction to the Study of Stellar Structure (New York: Dover)
- EQ_EOSideal0A — In C67, the ideal gas equation of state is initially written in terms of the specific volume <math>~V</math>, instead of the mass density <math>~\rho</math>; also, it is initially assumed that <math>~\bar{\mu}</math> = 1. Both <math>~\rho</math> and <math>~\bar{\mu}</math> are introduced in §III.1, Eq.(5).

[LL75] Laundau, L. D. & Lifshitz, E. M. 1975 (originally, 1959), Fluid Mechanics (New York: Pergamon Press)
- EQ_Continuity01 — LL75 present the Eulerian, rather than the Lagrangian form of the Continuity equation.
- EQ_Euler01 — In the Euler equation, LL75 do not initially include a source term to account for a gradient in the Newtonian gravitational potential, <math>~\Phi</math>; a term representing acceleration due to gravity, <math>\vec{g} = -\nabla\Phi</math>, is introduced in Eq.(2.4), but in LL75 this is intended primarily to describe gravity at the surface of the Earth.
- EQ_FirstLaw01 — LL75's Eq.(2.5) must be combined with their discussion of what they refer to as the familiar thermodynamic relation (between LL75 Eqs. 2.8 and 2.9) in order to appreciate the similarity with our expression.
- EQ_Poisson01 — In LL75, the symbol <math>\Delta</math>, rather than <math>\nabla^2</math>, is used to represent the Laplacian spatial operator.
- EQ_EOSideal0A — In LL75, the ideal gas equation of state is written in terms of the specific volume <math>~V</math>, as well as in terms of the mass density <math>~\rho</math>.

[BT87] Binney, J. & Tremaine, S. 1987, Galactic Dynamics (Princeton, NJ: Princeton University Press)
[KW94] Kippenhahn, R. & Weigert, A. 1994, Stellar Structure and Evolution (New York: Springer-Verlag)
[P00] Padmanabhan, T. 2000, Theoretical Astrophysics. Volume I: Astrophysical Processes (Cambridge: Cambridge University Press); and Padmanabhan, T. 2001, Theoretical Astrophysics. Volume II: Stars and Stellar Systems (Cambridge: Cambridge University Press)
- EQ_Poisson01 — See also Vol.I: §10.4, Eq.(10.58).

User:Tohline/Appendix/Equation templates

Key Equations

Key Parallel (Printed Text) References (spanning 5+ decades)

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