Why Earlier Scientists Could Not Guess about gravitational Force?(I am A ninth grade student of Matric so plz give an answer of my level,thanks in advance)

Why Earlier Scientists Could Not Guess about gravitational Force?(I am A ninth grade student of Matric so plz give an answer of my level,thanks in advance)
Guess what about gravity?
And science isn't about "guesses" anyway.
Newton used the Kepler's laws of planetary motion (based on data about the motion of the planets that Kepler had collected) and realised that the same description of the motion of things on Earth could also apply to the motion of the planets; he showed that Kepler's laws could be derived from his law of gravitation.
Why did it happen than and not earlier? Well, to some extent, you can always ask that. In this case it took the background information (from Kepler), and someone with the mathematical ability and interest to work it out (Newton).
A bit more background here:
Newtonian Gravitation and the Laws of Kepler
http://www.mtholyoke.edu/courses/mdy.../orb_lect.html
p.s. I don't know what ninth grade is, so I hope that is the right level!
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