hi, my physics book has a little picture of a magnetic bottle but does not really explain why the force always points to the center. Can you explain it to me. The magnitude of the velocity can never change when in a magnetic field, but the particle will be in Simple harmonic motion inside the bottle because it goes back and fourth. This means the velocity along the axis of the bottle has to change between -v to 0 to v. So it has to be gained somewhere else. Is this gain in how big the rings become, or is it gained in BOTH going faster along BIGGER rings. Im having trouble drawing a diagram to see that the force does point to the center. Every time I try it, I find that the as the magnetic field starts to curve, the component of velocity along the axis of the bottle goes down. But the gain in velocity is along the spiral path. This does not make much sense, because this would not mean a force pointing to the center of the bottle. It would just always point to the center of circular spiral like a centripital force does. Thanks for any help you give me.