Hi all! I'm not so good at physics so i decided to turn to you. So please help me. 1. The problem statement, all variables and given/known data I have to calculate how the object (ball) moves when droped into the tunnel (as seen in the picture), and how long the journey takes. We assume that Earth is round and there is no friction and air resistance and Earth density is constant. http://www2.arnes.si/~vvztrzin/pic.jpg [Broken] 2. Relevant equations 3. The attempt at a solution I tried going throug with lagrangian, but i found it hard, how to calculate gravity energy, because the mass of the Earth is larger on the left than on right. I appreciate all your help.