gravitation

[amaresh92]

what will be the gravitational force inside a hollow cylinder at the center?
if it is zero than explain why?
above thanks

[Petr Mugver]

If the cylinder has finite length, the field inside is zero only at the "center of the center", by symmetry considerations, and this even if the cylinder is not empty. If the cylinder has infinite length, then the field inside is zero not only along the axis, but in the whole region where there is no mass. The proof is the Gauss or divergence formula and the fact that for the gravitational field

\nabla\cdot E=4\pi G\rho.

[amaresh92]

what is meaning by center at center?

[Petr Mugver]

The center of the circular section at half longitudinal height