Fill in the blank. the gravitational attraction between two objects will if one object acquires more mass.

Well,

The Second Universal Law of Gravitation states that "The gravitational attraction between two masses is directly proportional to the mass of each individual object."  That means that if one object gains mass and the other object retains its mass, then gravitational attraction between them will increase.

So, the missing word is "increase."

That's easy.  Once we cut through all the scientific jargon,
we realize it's as simple as: 

A person's weight on Earth increases if he acquires more food,
or puts stones in his pockets.