Question: Find the gravitational force between two objects. Use the fact that the gravitational attraction between particles of mass m1 and m2 at a distance r apart is Gm1m2/r2. Slice the objects into pieces, use this formula for the pieces, and sum using a definite integral.
Two long, thin, uniform rods of lengths l1 and l2 lie on a straight line with a gap between them of length a. Suppose their masses are M1 and M2, respectively, and the constant of the gravitation is G. What is the force of attraction between the rods?