LIQUID at rest on a given SURFACE in contact with it is called the thrust of liquid on that surface.The normal force (or thrust) exerted by liquid at rest per UNIT area of the surface in contact with it, is called pressure of liquid or hydrostatic pressure.If Po is the atmospheric pressure then for a point at depth h below the surface of a liquid of density ρ,Hydrostatic pressure P is given byP = Po + ρghCALCULATION:Given - height (h) = 1 km = 1000 m and density of water (ρ) = 103 kg/m3The atmospheric pressure is⇒ Pa = ρgh ⇒ Pa = 103 × 10 × 103 = 107 Pa ⇒ Pa = 100 atm [∵ 1 atm = 105 Pa]