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In my homework, I had to calculate the variation of the pressure with the altitude for a classical gas. I know that I should calculate the density of particles per volume element.

I found this pdf on the net (http://cannoli.mps.ohio-state.edu/phy847/phy847-p2.pdf) [Broken].

If you see the third page of the pdf, the author calculates the density by introducing a delta function of the form \delta(r_1-r).

My question is: Why the delta is written in this way?, I mean, why the delta chooses the particle number 1 while not choosing another one?.

I hope my english didn't stop me from explaining what I mean.

Camilo Jimenez

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# Homework Help: Bariometric formula in Statistical Physics (particle density per unit volume)

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