I will explain my question with an example:
Let's take two surfaces that have the same area:
Both surfaces are equal:
Surface A, Sa = 18 Surface B, Sb = 18
But now if we rotate those two surfaces around the (for example) x axis.
We obtain two different volumes:
Volume A, Va = 72*pi Volume B, Vb = 54*pi
I've no problem to apply the formula, but I found the result a bit counter-intuitive. We apply the "same" area (with different shape) around an axis an we obtain a different volume.
Why is that (intuitively) ?