I want to know
How the value of $g$ was found and what experiments did Newton conduct to land upon the value that we use, which is 9.8 m/s^2.
I tried to search for it but I couldn't find much of a satisfactory answer, actually, I couldn't any answer.
And also, to what extend have scientists found the $g$ to vary on Earth's surface i.e; how low has it dropped and how much up has it jumped as per known and calculated magnitude ? I just need to know know an estimation and where those places are. And have we seen or noticed any drastic changes around those areas ? What if Olympics or any such even was to be held there ? What if Usain Bolt was to run there ? And also, how much can Gravity affect our health ? I was also wondering can we Punch in Space (Or in a place with very low to no gravity like Moon) and can we sprain ourselves by hasty haphazard movement of limbs etc. ?
And also, how did we come to know that Earth is tilted ? On seeing any photograph of earth, it looks straight to me. I have heard how it happened (due to some collision) and we know so due to the polar ends being away from the centre. But cannot it be that it was always like that ?
And one more thing, why doesn't Newton's Laws work on subatomic level ? Or Does it ? While I was studying Electricity, it was clearly mentioned that it complies with Newton's Law but it didn't seemed to be the case and when I consulted many people including teachers and students, I got mixed answers. Some said it does work but that the particles or so minutely small that all the force exerted becomes close to negligible and another one that I got was that it simply doesn't work at that small of a scale since those are fundamental or elementary particles.
While both of them seem good and true, the force cannot be negligible because then the electrical and other such forces should also be nullified (or it could be that when they sum up for a big particle, a big chunk, they become more identifiable and visible and less negligible (and so the electrical force must be the same or alike, that is that they should also act more prominently when occurring in greater amount (seems as if this is the case, but not sure)) and in case if it doesn't work at that level, then it shouldn't occur in bigger matters too because those small particles constitute up to being a big thing, I think.
I was about to say something else too but I can't recall right now because I was too delved in writing all that, but that is okay.
I am very much interested in knowing derivation of things (scientific, mostly) because it makes things easy for me to not only understand but to have it in head in a way that I could rephrase it instantly without much effort.
Please don't consider this to be a bogus, stupid and stubborn question like many other people around me do.
And also, please don't mark this as 'unclear' because I think I have explained in a simple and a neat way but if not, I will try to rephrase it (with letting this whole thing still being intact).
Additional Notes And Questions :-
Why do we say 'Per Second Square(d)' when that means 1 second only ? (Square of one second with always be one second, I think)
Is there or can there possibly be (I do think so) any relation between the square of value of pi to one decimal place and the value of speed of gravity (both are 9.8) ?