Anything that has a mass and a velocity has a kinetic energy , k=1/2mv^2 (when v does not approach the speed of light).
a falling object, let's say it starts at height H. at height h, it has potential energy P=mgh.
as it falls, h becomes lower than initial height H. thus, P decreases.
but, energy is conserved! E=P+K at all times, and E initial=E final (all things accounted for).
thus, as P decreased, K increases.
initially, t=0, P=mgH, K=0.
when the object has reached height h=0, it has P=0, K=P initial (= mg*H).
all along the path of falling, P decreased by m*g*deltah, K increases by m*g*deltah, where the object falls deltah.
then, its speed at every point is given by v=sqrt(2*k/M)
hope this presents a unified treatment of this topic.