Hi, I just started a course in drilling and the first chapter is about various situations where pressure drops in the drill string (pipe) causes forces on the pipe. I understand that a pressure drop due to friction causes a downward force on the pipe. The fluid is "pulling" the pipe down. However, when equipment in the pipe (such as a pump) is using energy from the fluid flow as its energy source, and there is a pressure drop due to this. Why is there a downward force on the pipe? At the nozzle of the pipe there is also a pressure drop, which causes a downward force on the pipe. Again, why does a pressure drop cause a downward force on a pipe? Hope my question is understandable :) Thank you!