And, the question is this.

Suppose we have some surface which is submerged, say below water surface.

For example, the water in this tank here and for example the bottom surface here.

If this is horizontal, the pressure there is horizontal,

the pressure there is constant rather.

So the pressure, the force there is just the pressure multiplied by the area.

And this force I can replace with some resultant force which I'll call FR.

But, what about the vertical faces here?

In this case, the pressure is increasing linearly downwards

according to our hydrostatic pressure distribution.

And, again, I will have some resultant force here, which is

pushing on this plane, and in this case, it's going to be pushing to the left.

So the most general question is,

if I have some arbitrary plane surface of arbitrary shape, arbitrary inclination,

what is the magnitude of the resultant hydrostatic force acting?

Where does it act, and what is the direction of the resultant force?

And those are the issues we're going to address in this segment.