When book trying explain on liquid pressure, they always explain by mathematics sense. But what i dont understand is that the book always treat liquid as macroscopically one big system [to find a mass by $\rho × volume$] instead of discrete liquid molecule (example if you dive under water the pressure are calculate by the weight of water above you). If you ask me why not. In solid the particle are stick together but for fluid [liquid] they are different where they can flow.

So my question is, why do they treat liquid in that way in order to find pressure? If the answer is that they won't be any different, then can anyone provide some explanation regarding that?

  • $\begingroup$ typing error microscopically = macroscopically* $\endgroup$
    – Sir.Plz
    Commented Sep 25, 2017 at 6:53
  • $\begingroup$ Then edit it. Give a note that you have edited, a similar there is an answer already pointing out that. Or after editing, post a comment below the answer. $\endgroup$ Commented Sep 25, 2017 at 15:12

1 Answer 1


First of all you must know that liquid is treated macroscopically,not microscopically. We consider a macroscopic volume to find pressure. It is obvious as pressure is a macroscopic property like volume, temperature etc. On microscopic level pressure may be calculated using kinetic theory of fluids.


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