Gravitational Force between Two Spheres
Snapshot 1: objects of mass 5 kg and 4.62 kg, 5 meters apart, have a force between them of
Snapshot 2: objects of mass 9.19 kg and 6.14 kg, 8.71 meters apart; force equals
Snapshot 3: objects of mass 1 kg and 10 kg, 6.28 meters apart; force equals
Special thanks to the University of Illinois NetMath Program and the mathematics department at William Fremd High School.
 J. S. Walker, Physics, San Francisco, CA: Pearson Addison-Wesley, 2010.
 J. C. Villanueva. "Gravitational Constant." (Jul 19, 2009) www.universetoday.com/34838/gravitational-constant.