man its all relativity, a forum would not be enought to explain it, one could explain it verbally but that'd still be long. i dunno how old u are but if u're in high school +/- u'll learn more about it in the univ... i'm taking dynamics right now, it consists of lots of relative stuff not really relativity in depth but still.. first thing to keep in mind is earth already rotates and mass of earth's ratio to ppl's mass, i'd say ppl's mass is considerably low. so don't expect too much of an orbit change, but it'll be fun to watch ppl jump its just another occasion to have fun after all. i hope ppl won't kill each other after no orbit change