Because lager objects have much more room for mass the smaller objects. take the earth as an example the earth is very big and has alot of mass in it which makes gravity that pulls us down when we jump up.
The mass number is the summation of number of proton and neutron present in a nucleus of an atom. For the neutral atom the number of positive charge (number of proton) must be equal to the number of electrons. The number of electrons present in an atom is the atomic number of the atom. The standard way to express the mass number (a) and atomic number (m) of a atom (say X) is
. Now for silicon number of electron or atomic number is 14. And the mass number (a) given 29. Thus the expression nucleus of silicon will be 
Sodium, Carbon, Oxygen, Hydrogen, Nitrogen, Phosphorous, and Sulfur.
I have no idea, but i’m pretty sure you gotta divide
Protons and Electrons charges are the exact same size.