If you were to replace all of these forces by a single force such that the (first) moment of this force about a line through the surface of the fluid is the same as the (first) moment of all the actua...If you were to replace all of these forces by a single force such that the (first) moment of this force about a line through the surface of the fluid is the same as the (first) moment of all the actual forces, where would you place this single force? You would place it at the centre of pressure.
