Hi (I hope I'm posting in the right place) In physics class we are currently working with projectories of comets etc. that reach the orbit of planets, and get pulled in by its gravity. My teacher is currently doing the work in an excel document, but has requested a better solution for calculating the projectories. Does anyone know of a program (freeware is prefferable) that can simulate such projectories with a graphic interface? Or has any ideas of how it could be accomplished without having to do it in excel? Any comments on the matter appreciated.