# Hydrostatic Pressure

• A fluid’s own weight causes the fluid to be pressurized.
• Within the fluid, each fluid molecule exerts repulsive forces against all its neighboring molecules. • Against a foreign object, the fluid exerts repulsive forces in the direction perpendicular to the surfaces of the foreign object. • Each point in a fluid can be ascribed a quantity called the static fluid pressure p, which is the repulsive force per unit area exerted by the fluid at that point.

• By considering the pressure force Fp required to support a vertical column of fluid’s weight W, we can deduce that \begin{aligned}{{F}_{p}}&=W\\pA&=mg\\pA&=\rho Vg\\pA&=\rho hAg\\p&=h\rho g\end{aligned} • Amazingly, hydrostatic pressure at a point is not affected by the shape or volume of the fluid above it. It is only dependent on the vertical height h of the fluid above it. • And yes the atmosphere is also a fluid with weight. So the atmosphere is also pressurized. In fact, the atmospheric pressure at sea level is about 100 000 N per m2.