1. The problem statement, all variables and given/known data Infinitely long rod with the z axis at its center. The rod has a uniform mass per unit length [itex]\mu[/itex]. Find the gravitational force vector F on a mass m, at a distance [itex]\rho[/itex] from the z axis. 2. Relevant equations F=-G*(M*m)/R^2 (times radial unit vector rhat for the vector form) 3. The attempt at a solution I believe I can treat the rod as being very thin, with a center of mass along the z axis. Then I labeled the masses position as being on the y axis. I believe that the force exerted on m in the z direction cancel because of symmetry. I believe I need to work in cylindrical polar coordinates because of the problems use of [itex]\rho[/itex] and z. I do not see how to construct an integral (from - infinity to + infinity) in polar coordinates. I know I need to vary z. I tried to construct an equivalent integral in Cartesian coordinates as follows. -G[itex]\mu[/itex]m[itex]\int[/itex]dz/(y^2+z^2) G is the gravitational constant. integral from -infinity to infinity M= mass of 2nd object in Newton's law of gravitation was replaced by [itex]\mu[/itex]*z r= distance from z axis= (y^2+z^2)^1/2 y is a constant because the mass is always a the same y position. But I think this is wrong. Can someone help?