"Consider the earth following its nearly circular orbit about the sun. The earth has a mass mearth=5.98x10^24kg and the sun has mass msu=1.99x10^30kg. They are separated, center to center, by r=93 million miles = 150 million km." What is the size of the gravitational force acting on the earth due to the sun? I'm still setting up the problem... I think I use the equation Fg=G(m1m2 / r2). r is the distance between the centers of the two objects. G is the gravitational constant (so I just leave that as G, right?) But, is the sun or the earth m1?