An example of a system with decreasing gravitational potential energy is a ball in free fall.
At its initial height h, the ball has a gravitational potential energy equal to
[tex]U=mgh[/tex]
where m is the ball mass and g is the gravitational acceleration. As the ball falls toward the ground, its height h decreases, and so its gravitational potential energy decreases as well, according to the formula
[tex]U=mgh'[/tex]
where h' is the new height of the ball.
