I was thinking, the amount of "gravity" a person feels on the surface of a planet is not only dependent on gravity, but also the centripetal force... For example, if earth spun 17.04 times as fast as it does now (i.e. 1 day = 1.4 hours) then anything on the surface of the earth would essentially be orbiting it, and would feel weightless! Also, a planet with much more mass than earth could have the same effective gravity at the surface if it had a larger radius or rotational velocity. The only thing thats a little fuzzy to me is the effects this would have on actually launching things into space. A planet with higher mass and velocity with the same effective gravity on the surface would still make require much more energy to launch a mass into space, right? Discuss.