This is College Physics Answers with Shaun Dychko. Here's the equation for Newton's universal law of gravitation and it says that as you increase the mass, you will increase the force because this force is proportional to each of the masses and then as you decrease the distance between the objects, you will increase the force of gravity because the force of gravity is inversely proportional to the square at that distance. So decrease in the distance by a half will increase the force by 4 times.
Given Newton's universal law of gravitation, under what circumstances is the force due to gravity maximized?
The force of gravity increases with increases in mass of either body, or with a decrease in the distance between the bodies.