Gravity

Gravity is a natural phenomenon. Accurately described by Albert Einstein in 1915. Every object in universe is exerting force on other objects. Gravity is directly proportional to Mass (sometimes refers as weight, in normal conversation) that means heavier the object will be more gravitational force it will exert. Gravity is also indirectly proportional to distance     i.e. more the distance will be lesser force it exert.

However gravity is attractive force (it always attract other object). Earth is constantly attracting you towards the surface. The force an object exert on the other can be calculated by:
            F=G×M×m/r×r
Where G is gravitational constant equals
6.674×10^-11 Nm^2/kg^2

Using this formula scientists accepted 9.80665 m/s as gravitational force of earth.

According to Newton's 3rd law every action has equal and opposite reaction. If earth attract some object it move towards it till they collide though If the object is smaller it will move relatively fast than earth.

It raisen a question
Why moon doesn't collide with earth?

I'll answer that for sure but in another blog.

Read more: here