复习Pressureatapointhas thesamemagnitudeinalldirections,andiscalledisotropic.ZFreesurfaceAirp=ogageLiquidh=-h
Pressure at a point has the same magnitude in all directions, and is called isotropic. 复习
复习Thepressure isthe same at all points withthe same depthfrom thefree surface regardless of geometry,provided thatthe pointsare interconnected bythe samefluid.However, the thrust due to pressureis perpendicular to thesurface onwhichthe pressure acts,andhence its directiondependsonthegeometryWaterMercuryPA=Pg=Pc=P=PE=Pp=PG=Patm+pghPH+PI
The pressure is the same at all points with the same depth from the free surface regardless of geometry, provided that the points are interconnected by the same fluid. However, the thrust due to pressure is perpendicular to the surface on which the pressure acts, and hence its direction depends on the geometry. 复习
复习3)Hydrostatics equation:when the densityis constantthe pressure in a liquid at rest increases linearly withdepthfromthefree surfacedp-pgdzH20Zp=-pgz+poNz2HgPbelow = Pabove + Pgz
复习 3) Hydrostatics equation: when the density is constant, the pressure in a liquid at rest increases linearly with depth from the free surface. 0 p gz p below above p p gz d p g d z
4.6PressureMeasurementandManometers3）Differentialmanometer（差压力计）Adifferentialmanometercanbe5usedto measure the differenceinpressure between two containers(4)Yior two points in the same system.Again,onequatingthepressuresn(1at points labeled (2) and (3), wemaygetan expressionforthe(3)pressure difference between Aand B:PA- P = 2h +3h -h
4.6 Pressure Measurement and Manometers 3) Differential manometer (差压力计 ) A differential manometer can be used to measure the difference in pressure between two containers or two points in the same system. Again, on equating the pressures at points labeled (2) and (3), we may get an expression for the pressure difference between A and B: A B 2 2 3 3 11 pp h h h
4.6PressureMeasurementandManometersIn the common case when A and B are at the same elevation(h = h +h) and the fluids in the two containers are the same (y=ys)one may show that the pressure difference registered by adifferential manometer is given by51where(3)2Pm is the density of the manometer fluid,p is the density of the fluid in the system,h is the manometer differential reading
4.6 Pressure Measurement and Manometers hhh 1 23 1 3 In the common case when A and B are at the same elevation and the fluids in the two containers are the same one may show that the pressure difference registered by a differential manometer is given by 2 1 m p gh m h where is the density of the manometer fluid, is the density of the fluid in the system, is the manometer differential reading