1. The problem statement, all variables and given/known data The formula of the force exerted on the fluid by the pipe is P1A1 –Fx – P2A2 , I don’t understand why the P1A1 is positive ? 2. Relevant equations 3. The attempt at a solution Assuming to the right is positive , shouldn’t the force acting on the water = -P1A1 ? Because the water is flowing from left to right , the force acting on the water by the pipe should be in oppostite direction( which is –P1A1 ) , am I right ?