Curious about parts of the velocity flow formula

I'm taking hydraulics this semester, and am trying to understand all parts of the formulas we use so I can hopefully actually grasp the concepts instead of simply crunching numbers. We went over the velocity flow formula the other day and the formulas we used were

V=12.14(square root of the pressure) when the pressure is known,

or V=8(square root of Head ) when the head pressure is known.

I can't find a correlation for either number in the above formulas. It seems like the number being multiplied is usually the weight of a 12" column of water i square inch at the base, or some other real world reference, and it seems like where the book is using a technical coefficient, it refers to the number in those terms. With these formulas, however, it simply dumps the numbers out and moves on. What exactly am I multiplying together here? Any help would be appreciated. We're using the Brady 3rd edition of FD Hydraulics.

Thanks!