Editing VE (section)

===First-Order Virial Equations===
[<b>[[Appendix/References#EFE|<font color="red">EFE</font>]]</b>, &sect;11(a), p. 21] <font color="#007700">The [virial] equations of the first order are obtained by simply integrating [the Euler equation] over the instantaneous volume, <math>V</math>, occupied by the fluid</font>.  Specifically, using our H_Book variable notation,
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<math>\int\limits_V \rho \frac{dv_i}{dt} d^3x</math>
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<math>=</math>
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<math>- \int\limits_V \frac{\partial P}{\partial x_i} d^3x - \int\limits_V \rho \frac{\partial \Phi}{\partial x_i} d^3x \, ,</math>
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leads to (see [<b>[[Appendix/References#EFE|<font color="red">EFE</font>]]</b>] for details),
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<math>\frac{d^2 I_i}{dt^2} </math>
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<math>=</math>
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<math>0 \, ,</math>
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where the <span id="MomentOfInertia">moments of inertia</span> about the three separate principal axes <math>(i = 1,2,3)</math> are defined by the expressions,
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<math>I_i</math>
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<math>\equiv</math>
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<math>\int\limits_V \rho x_i d^3x \, .</math>
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Thus, the first-order virial equation(s) <font color="#007700">expresses the uniform motion of the center of mass of the system</font>.