Question

two books are kept at extreme ends of a table top why don't they move towards each other due to gravitational pull?

Answer 1

two books are kept at extreme ends of a tabletop they don't move towards Each Other because the gravitational pull between them is so small, so small that it is just negligible
We find the force of attraction between two bodies by this formula:
F = G × (M x m / r ^2)
Where F is the force of attraction between the two bodies, G is the gravitational constant (6.67 × 10^-11 N m^2 kg^-2), M is the mass of one body, m is the mass of another body and r is the distance between them. Now considering the mass of one book to be 5 kg and another is 10 kg and the distance between them to be 1 metre, the sum will go:
F = G x (M x m / r ^ 2)
F = 6.67 × 10 ^ -11 × (5 x 10 / 1)
F = 6.67 x 10 ^ -11 × 50
F = 3333.5 x 10^-11
F = 3.3335 x 10 ^ -8
This is in scientific notation. The actual number would be 0.000000033335 N.
Now, considering the mass of a man to be 50 kg and the mass of Earth is 5.983 x 10^24 kg, while the distance between them to be 1 metre,the sum comes:
F = G x (M x m / r ^ 2)
F = 6.67 x 10 ^ -11 x (50 x 5.983 x 10^24 / 1)
F = 6.67 x 10 ^ -11 x 2.9915 x 10 ^ 26
F = 1.9953305 x 10 ^ 16
Therefore the Earth attracts a body of 50 kg witha force of 1.9953305 x 10 ^16 N. So, therfore, the force of attraction acting between two books kept on a table is very negligible as compared to the Earth attracting a body of 50 kg.