Well, sorry for my english but I'm not mother tongue.
I would say that we can experiments gravity every day, see this formula:
F= (G*M*m)/d*d
F is the attraction between M (that is the earth) and m (that can be another planet, a star, or you!). G is an universal constant that's equal to 6.67*10^-11.
d is the distance between M and m.
This show that's equal if m is you or a planet, and it shows because a thing fall down.
Furthermore I said the earth is a geoid, so it isn't perfectly spheric, north pole and south pole are little crushed, about 20 kilometers than a sphere.
Having said that I have another question: how can you explane me volcanism?