What is the relationship between y_c and y_R in fluid mechanics?

[aaronfue]

Homework Statement

During the calculation of y_R in fluid mechanics problem, hydrostatic force on a plane surface

Homework Equations

y_R = y_c+$\frac{I_xc}{y_c×A}$

The Attempt at a Solution

I can see how it is calculated but I've read through the chapter and I don't see how it is described. The textbook is Fundamentals of Fluid Mechanics (6th Ed.) by Munson.

 

[SteamKing]

It looks like yc is the location of the centroid of the gate, while yR is the location of the resultant of the pressure acting on the gate, or the center of pressure.

This article (pp. 6-8) gives the derivation and an example calculation:
http://www.freestudy.co.uk/fluid mechanics h1/outcome11.pdf