GRAVITATION edit
Gravitation is type of force that is applicable for every object in this universe.It is a force that is having any mass,and pulls towards it surface.it is applicable for all the attraction in huge celestial object in this universe. The force that causes acceleration and keep the body moving along the circular path is acting towards the center.this force is called centripetal force.in this absence of this force, the body flies off along a straight line.that line will be tangent to the circular path.the motion of moon around the earth is due to the centripetal force,this force is provided by the force of attraction of the earth.
UNIVERSAL LAW OF GRAVITATION edit
Every object in this universe attracts every other object with a force ,that is proportional of the product of their masses and inversely proportional to the square of the distance between them.the universal law of gravitation was discovered by Sir Issac Newton. That is, F∝M×m and F∝1/d2 combining the equation F∝M×m/d^2 there is a constant of gravitation that is expressed in the form of G. G=F×d^2/M×m the constant of or value of G was discovered by Sir Henry Cavendish (1731-1810)by using sensitive balance.THE accepted value of G in 6.673×10-11N m^2 kg^-2.
Inverse-square edit
If F is inversely proportional to the square of d means,for example, that if d gets bigger by a factor of 7,F becomes 1/49 times smaller.
An Example: mass of earth=6×1024kg mass of moon=7.4×1022kg distance between the earth and the moon is 3.84×105km
d=38400 km or 3.84×105km
=38400×1000m or 3.841×105×102m =38400000m of 3.84×108m
G=6.7×10^-11 Nm2kg-2 ∴F=GMm/d2
6.7×10-11Nm2Kg-2×6×1024kg×7.4×1022kg/(3.84×10^8m)2 =2.01×1010 N