Newtons law about gravity.
(According to Isaac Newton, an object in the room that gets a curved route / direction will create gravity)
(Source: http://www.history.com/shows/the-universe/videos/beyond-the-big-bang-sir-isaac-newtons-law-of-gravity)
Its of course more then this.
But to me it only leaves me with more questions then answers.
It make me understand what create gravity and the effect it have.
But it still dont answer the most important question.
What is gravity exactly?
(the easy answer will of course be the sling effect)
but that is still a hollow answer if we want a serious scientific answer for it.
The sling effect alone should also make us less heavy on "the outer side" of the planet compare to "the inner side" of the planet, but that is not the case.
The fact is that the only geographic position on our planet that make any difference on our weight, is the distance from the center of the planet we are.
So your weight on top of a mountain will be a little lesser then it is in the bottom of the valley beside this mountain.(i believe)
There is also some other things that we should be able to measure if it only was Newtons laws that was the cause of things.
For example we should be able to see the difference on the weight of things when the Earth was closer to the sun, compare to when it is far away from it. (maybe it is too, and it is just me that have not read about it)
Just like we should be more heavy at day, compare to when the moon is strait above us.
https://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation