Fluids -- bringing together pressure, depth and friction Hi Again! More troubles with fluids. I was pretty sure I had this one. There is a freshwater pond density, D=1000 kg/m^3 depth = 15.1 m one of the sides is blocked off by a cliff. A nearly horizontal tube diameter = 3.17 cm depth below the pond's surface is 6.2 m eroded to the other side of the cliff a rock blocks cuts off the flow of the water. The question asks for the frictional force between the tube's wall and the rock blocking the exit. I figured it would be fairly easy, since F = P*A and we can find out the hydrostatic pressure. so P = Patm + D*g*h P = 101300 + 1000*9.8*6.2 P = 162060 Pa A = pi*r^2 = pi* (0.01585)^2 = 7.89e-4 m^2 and therefore, F = P*A = 127.9 N is the force on the rock blocking the exit because there is no acceleration, the system is at equilibrium so Fnet = F(ontherock) - F(friction) = 0 so F(on the rock) = F(friction) so then my answer would be 127.9 N Could you point out where I've made an error, and push me in the right direction?