William Finley is quite dead according to Wikipedia

The whistleblower behind the recent Boeing safety scandals, that has casually killed himself on a day he was supposed to give a deposition or something

Well, not to be that guy (actually definitely to be that guy) but what Newton discovered was that gravity was proportionnal to the mass of the bodies, and to the inverse of the square of the distance between their center of mass, and this second point seems too difficult to prove for a 9 years old.