流功学 dP=(p dydz-p,AABC cos(n, x)) 2 +(p,-dxdz-p, AABC cos(n, y)j +(p. dxdy-p,AABC coS(n, z)k 2 =(PxPn)ddi+(Py-Pn)x与+(P:-Pn)d水 (2—3) 16
16 p p dydzi p p dxdzj p p dxdyk p dxdy p ABC n z k p dxdz p ABC n y j dP p dydz p ABC n x i x n y n z n z n y n x n 2 1 ( ) 2 1 ( ) 2 1 ( ) cos( , )) 2 1 ( cos( , )) 2 1 ( cos( , )) 2 1 ( = − + − + − + − + − = − （2—3）
The mass force on the infinitesimal fluid dF=PC∥=p2y(1+/+厂)(24) 6 If the fluids are in balance state. according to df +dF=0 simplify the formula and get the results Pr-p, dx=o 3 P,=Pn+fyp dy=0 (2-5) p-=p+fpd=o 3 7
17 If the fluids are in balance state. According to ， simplify the formula and get the results: dF + dF = 0 m 0 3 1 0 3 1 0 3 1 − + = − + = − + = p p f dz p p f dy p p f dx z n z y n y x n x （2—5） ( ) 6 1 d F dV f dxdydz f i f j f k m m x y z = = + + （2—4） The mass force on the infinitesimal fluid：
流其功学 微元流体上的质量力为: dF=PC∥=p2y(1+/+厂)(24) 流体处于平衡状态,根据n+dF=0,简化后有: pn+fp dx=0 3 py-ptfyp-dy (2-5) 3 p.-ptfpdz=o 18
18 流体处于平衡状态，根据 dFm + dF = 0 ，简化后有： 0 3 1 0 3 1 0 3 1 − + = − + = − + = p p f dz p p f dy p p f dx z n z y n y x n x （2—5） ( ) 6 1 d F dV f dxdydz f i f j f k m m x y z = = + + （2—4） 微元流体上的质量力为：
when dx, dy and dz go to zero the wedge-shaped lessens to a point O. The pressures Px, Py, p= and pn on any points turn into the fluid static pressure at point O in all directions. So we can get Px=Py=p=Pn (26) The fluid static pressures on different space points are different to each other normally. That is to say the fluid static pressure is a continuous function of space coordinates p=p( (27) 19
19 The fluid static pressures on different space points are different to each other normally . That is to say the fluid static pressure is a continuous function of space coordinates. p = p(x、y、z） （2—7） px = py = pz = pn （2—6） dx , dy dz px py pz pn when and go to zero the wedge-shaped lessens to a point O . The pressures , , and on any points turn into the fluid static pressure at point O in all directions. So we can get
流其功学 dx、c、c趋于零时,四面体缩到O点,其上任何一点 的压强PPP、Pn就变成O点上各个方向的流体静压强, 于是得到 Px= P=p=p 2-6) 不同空间点的流体静压强,一般来说是各不相同的,即 流体静压强是空间坐标的连续函数 p=p(x、y、z) (2—7) 20
20 不同空间点的流体静压强，一般来说是各不相同的，即 流体静压强是空间坐标的连续函数。 p = p(x、y、z） （2—7） px = py = pz = pn （2—6） dx、dy、dz px、py、pz、pn 趋于零时，四面体缩到O点，其上任何一点 的压强 就变成O点上各个方向的流体静压强， 于是得到