8 2-2 Fluid Static Pressure and Its Characters Definition The pressure in the equilibrium fluid is called fluid static pressure. It is expressed byp △PdP (2-1) In the formula A4→0△AdA AA--area of infinitesimal unit △P— the total pressure acting on the surface of△A Vector expression of fluid static pressure on the surface of infinitesimal unit is dP=-pdA (2-2) The minus shows that the direction of fluid static pressure goes along the inner normal direction of the compression face Characters The magnitudes and directions are all have relation to the compression face 77 §2-2 Fluid Static Pressure and Its Characters Definition： dA dP A P p A =   =  →0 lim （2—1） In the formula: ——area of infinitesimal unit ——the total pressure acting on the surface of A P A Vector expression of fluid static pressure on the surface of infinitesimal unit is dP pdA   = − （2—2） The minus shows that the direction of fluid static pressure goes along the inner normal direction of the compression face. Characters： The magnitudes and directions are all have relation to the compression face. p The pressure in the Equilibrium fluid is called fluid static pressure. It is expressed by