I'm curious too, if a model earth was made, say, 200 miles in diameter (I believe the atmosphere is 300 miles high), how noticeable the curvature would be if you were standing on top of it. Without having the calculation of the curvature in inches per 100 feet and/or per mile in front of me, I wonder what the noticeable change would be as a person walks across the top toward what one might consider the side from a great distance.
Newton's third law is that all objects possess gravitational pull.
Maybe outside of the practical impossibility, the 200 mile diameter sphere couldn't overcome the pull of the earth, or, maybe it could? Perhaps if there was enough of a distance between the sphere and the earth?
I'm sure these ideas and formulas have been solved many a time. Regardless, the size of the large of the object and the converse size of the pulled object work together.