Hydrostatic Pressure
Definition
The pressure in a still fluid that grows with depth — why your ears pop diving deep.
Unit: Pa
Technical definition
P = P₀ + ρgh: pressure at depth h equals surface pressure plus fluid density × gravity × depth. It acts equally in all directions (Pascal's principle) and depends only on vertical depth, not container shape.
Example
At 10 m underwater, pressure is about 2 atm — one from the air above plus one from the water column. That is why divers equalize their ears.
Common confusion
Hydrostatic pressure depends on depth, not on how much water there is total. A narrow tube and a wide lake give the same pressure at the same depth — the hydrostatic paradox.