I need to settle an argument. I think gravity causes a column of water to exert greater pressure against the walls of a pipe in which it is contained as it is tilted from horizontal to vertical. In other words, the pressure in supply pipes from a remote elevated water source would be increased at the destination from what it was at the source depending upon the length of the pipe and the degree of incline. Right or wrong?


The pressure at the bottom of the column of water is the weight of water above each bit of area.

If the column is vertical then it is the weight of the full height of that column, if you lay the pipe horizontally then the pressure on the bottom edge of the tube is only the thickness of water lying in the tube


The total pressure is conserved. When you tilt the column the pressure exerted at the bottom of the column is reduced. This increases the pressure at the walls of the column.

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    $\begingroup$ Are you sure about that? P = $P_{o}$ + $\rho \ g \ h$, where $P_{o}$ is some external pressure, $\rho$ = mass density of fluid (water here), $g$ = acceleration of gravity, and $h$ relative height. Unless the column is more than 1 km or so, $P_{o}$ will be roughly constant but $\rho \ g \ h$ will change significantly at the bottom of the column but not at the top. $\endgroup$ Oct 25 '14 at 15:50
  • $\begingroup$ What makes you think pressure is a conserved quantity? $\endgroup$
    – Sean
    Oct 27 '14 at 1:38

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