I'm quite new to physics and I don't totally understand the concepts of potential energy and work. I've been watching MIT courses and I got pretty confused, considering the following situation:
We have 2 charges: +4 and -1. At the top there is a point, where the eletric field is 0, which means there will be no force on a test charge that we place here, consequently it will gain no velocity and it will stay in place. But the electric potential at this point is not zero, moreover it becomes smaller, when we go above that point (in this picture). Charges tend to move from higher potential to lower potential, so according to this statement, the charge should be willing to go up. But there is no force that could push it. I'm pretty sure, I'm wrong at some point, so I would like you to explain this situation in details.