A stationary flow of a viscous fluid is maintained in a tube of variable cross section. In sections 1 and 2, the velocity can be assumed to be constant across the section. The areas of sections 1 and 2 are S₁ and S₂, respectively, and the pressure of liquid in them are P₁ and P₂, respectively. The velocity of the fluid flowing in section 1 is equal to v₁. Find the force with which the liquid acts on the pipe section between sections 1 and 2.
144
4.5 Fluid surface tension