Simplify the following text for a Grade 10 native English-speaking person.
Original: Thus , a book lying on a table has less gravitational potential energy than the same book on top of a taller cupboard , and less gravitational potential energy than a heavier book lying on the same table . An object at a certain height above the Moon 's surface has less gravitational potential energy than at the same height above the Earth 's surface because the Moon 's gravity is weaker .
Simplified: Gravitational potential energy cause 's objects to move towards each other .