Hydrostatic pressure — Hyunjoo Park

$p = \frac{F}{A} = \frac{mg}{A} = \frac{\rho Vg}{A} = \rho hg$ where $A$ is the area of the column, $V = Ah$ is the volume of the column of fluid/gas, $\rho$ is the density of the fluid/gas and $h$ is the height of the fluid/gas column. For liquids, which are nearly incompressible, this equation holds to great depths.

At the Earth’s surface, the air pressure you feel is a result of the gravitational weight of air above you. Underwater, $p = p_{atm} + \rho gh$ . Pressure changes with elevation because the mass above changes, not because $g$ changes.

$p_{atm} = 1\ \text{atm} = 1.01 \times 10^5\ [\text{N m}^{-2} = \text{Pa}] = 101\ [\text{kPa}]$ Standard atmospheric pressure, the average pressure at sea level.

Typical trap

The higher you go in the atmosphere, the less air there is, so $\rho$ is not constant. So instead of $\rho gh$ , use $p = \frac{M_{atm} g}{A}$ . Note that $A = 4\pi r^2$ , not $\pi r^2$ .