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In basic kinetic theory we often use cubes. For example, the derivation of the ideal gas law is done with a cubical volume. Is a cube necessary for it to work? If not, wouldn't a sphere be more symmetric and thus simpler?

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  • $\begingroup$ Can you be more specific? $\endgroup$ – Aaron Stevens Feb 20 at 4:39
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    $\begingroup$ Depends on the level of the presentation and the way you intend to balance hand-waving against grotty equations. $\endgroup$ – dmckee Feb 20 at 5:01
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    $\begingroup$ Write out the derivation in (x,y,z). Write out the derivation in (r,$\Theta$,$\psi$). Compare. $\endgroup$ – Jon Custer Feb 20 at 23:50
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Using a cube is an extension of the choice of coordinates used in the mathematical modeling. $dV=dxdydz$ is a small cube after all. $dV$ is more complicated in radial coordinates

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