If the bar magnet producing the magnetic field is rotating then there will be extra energy imparted if your magnet flies by in the same direction, but the World's gravitational field does not rotate, otherwise satellites going "against" the field would need far more energy to overcome this resistance, which is not observed in reality. Neville. philip madsen <pma15027@xxxxxxxxxxxxxx> wrote: As I said before, Philip, gravity slingshots are rubbish, since the speed gained on approach must be lost again on recession. Neville Yet I forgot something . Neville.. If jupiter was on a path away from the sun , at velocity N and the satellite flyby curved by in the same direction, would it not impart some extra pull away from the sun to the satellite? I imagined what if the magnet I was shooting at was rotating away from me when I shot the steel ball very close past it in the same direction.. Do we not have three forces acting on the ball.. One attraction in ...second partial capture which carries it along from its own motion, and the third the pull back which is equal to one, the atraction... This leaves the net force due to the rotation of the large magnet. Phil. PS and I just noticed, Allen come up with similar, except I used the orbital motion of the planet not the rotation... But I think that is what allen meant when he mentioned the magnet experiment.. thanks Allen --------------------------------- Yahoo! Answers - Got a question? Someone out there knows the answer. Tryit now.