Complete the statement. Assume that the book's mass did not change.
The gravitational potential energy stored between the book and Earth () as the book fell toward the ground.

 - decreased
 - stayed the same
 - increased
Think about how the distance between the book and the center of Earth changed.
The ground is lower than the bookshelf. As the book fell toward the ground, the distance between the book and the center of Earth decreased. So, the gravitational potential energy stored between the book and Earth decreased as the book fell toward the ground.