Characters of fluid Static Pressure 1. The direction always goes along the inner normal of the compression face. Incise the static fluid into two parts with an arbitrary plane, just as shown in Figure 2-1. Take the shadow part as partition, if the direction of the static pressure at a certain point m on incisory plane doesnt go along the normal direction but arbitrary, then p can be decomposed tangent component t and normal component pn. The static fluid dose not undergo shearing stress and pulling force or else the equilibrium will be destroied. So the only direction of static pressure is consistent with the normal direction on the acting face9 Characters of Fluid Static Pressure p  n p m Incise the static fluid into two parts with an arbitrary plane, just as shown in Figure 2—1. Take the shadow part as partition, if the direction of the static pressure at a certain point on incisory plane doesn’t go along the normal direction but arbitrary, then can be decomposed tangent component and normal component . The static fluid dose not undergo shearing stress and pulling force or else the equilibrium will be destroied. So the only direction of static pressure is consistent with the normal direction on the acting face. 1. The direction always goes along the inner normal of the compression face