两U形管的连通管内充满空气。若测压前两U形管压差计内的水银液面均为同一高度，测压后两U形管压差计的读数分别为R1、R2，试求a、b两点间的压力差p解：
p1?pa??wgh1a?pb。
，pa?p1??wgh1
4p1?p2，p2?p3??HggR1，p3?p4，p?p5??HggR2，p5?pb??wgh5
pb?p5??wgh5?p4??HggR2??wgh5
pa?pb?p3??HggR1??wgh1??p4??HggR2??wgh5?
??Hgg?R1?R2???wgh1??wgh5而 所以
h1?h?R12，
h5?h?R22
?R??R?pa?pb??Hgg?R1?R2???wgh??wg?1???wgh??wg?2??2??2???Hgg?R1?R2??11???wg?R1?R2????Hg??w??R1?R2?g22??